The Pennsylvania State University
The Graduate School
College of Health and Human Development
STRATEGIES FOR MANAGING NATURAL SOUNDS FOR HUMAN EXPERIENCE
AND ECOSYSTEM SERVICES
A Dissertation in
Recreation, Park and Tourism Management & Human Dimensions of Natural Resources and the
Environment
by
Lauren Abbott Ferguson
2018 Lauren Abbott Ferguson
Submitted in Partial Fulfillment
of the Requirements
for the Degree of
Doctor of Philosophy
August 2018
The dissertation of Lauren Abbott Ferguson was reviewed and approved* by the following:
Peter Newman
Professor and Head of Department of Recreation, Park and Tourism Management
Dissertation Co-Advisor
Co-Chair of Committee
B. Derrick Taff
Assistant Professor of Recreation, Park and Tourism Management
Dissertation Co-Advisor
Co-Chair of Committee
Andrew Mowen
Associate Professor of Recreation, Park and Tourism Management
Justine Blandford
Assistant Professor of Geography
*Signatures are on file in the Graduate School
iii
ABSTRACT
A large body of evidence suggests that there are benefits from natural sound exposure to
human wellbeing. Conversely, man-made noise, from transportation and urbanization, has
damaging effects on overall health measures. Large cities and urban areas are expected to be
highly impacted by elevated levels of noise, however National Parks, places where one would
expect to find quiet, are also at risk for noise pollution. Park managers are mandated to protect
natural sounds for the benefits to human experience. The purpose of this dissertation is to explore
methods that aim to better understand the impacts of noise on human experiences in National
Parks. Data for these studies were collected at two different National Park Service (NPS) sites:
Muir Woods National Monument, and Denali National Park and Preserve. In the first chapter of
this dissertation, the state of soundscapes research is introduced. Chapters 2 through 4 were
written as stand-alone manuscripts that present and discuss study findings. Chapter 5 summarizes
the combined results of the three dissertation studies.
Chapter 2 utilized spatial modeling data that predicted noise level across the United
States to measure factors that influence visitor perceptions of soundscapes at Muir Woods
National Monument. Study findings suggest that the combined effects of noise sensitivity, the
ability to hear natural sounds, and the estimated average sound level of home zip code impact
soundscape perceptions. A linear relationship shows that the louder predicted sound levels of
one’s zip code boundary, the less pleasant the soundscape was perceived.
Chapter 3 used a collection of varying audio clips to determine thresholds for propeller
aircraft noise in Denali National Park and Preserve. In this study, an innovative method for
measuring human response to noise was tested. Multiple regression models were used to predict
visitor thresholds related to aircraft sound levels, as well as, the number of flights tolerated per
hour and per day.
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Chapter 4 examined visitor preferences for soundscape management along the hiking
trails at Muir Woods National Monument. An experimental design was used to test differences in
preference between respondents who viewed management signs along the trail and a control
group (without signs). Results showed that visitors prefer to see signs along the trail, asking
visitors to maintain quiet. Also, visitors exposed to signs during their time in the park, had a
significantly higher preference for management signs than the control group.
Chapter 5 discusses overall findings. Results from this dissertation suggest several
important findings related to measuring park soundscape experiences. (1) Visitors come to parks
with individual norms, beliefs, etc., and now we know that their exposure to sound at home can
impact their perceptions of the park soundscape. (2) A randomized suite of varying sound levels
is effective in determining thresholds for noise. And (3) Visitors generally prefer indirect forms
of soundscape management. Together these findings suggest the high level of regard that visitor’s
place on protecting natural sound conditions. Ultimately, experiencing the benefits of natural
sound are valuable to the national park experience. Together park managers and social scientists
should continue to understand the human experience in relation to soundscapes so that future
generations can enjoy the benefits of natural sound.
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TABLE OF CONTENTS
List of Figures .......................................................................................................................... vii
List of Tables ........................................................................................................................... viii
Acknowledgements .................................................................................................................. ix
Chapter 1 Introduction ............................................................................................................. 1
What is a soundscape? ..................................................................................................... 3 The Importance of Sounds ............................................................................................... 4 Natural Sound and Resource Protection .......................................................................... 6 Indicators and Standards of Soundscape Quality ............................................................. 8 Natural Sound as an Ecosystem Service .......................................................................... 9 Methods Used in Natural Resource Management ............................................................ 12 Summary .......................................................................................................................... 16 Dissertation Purpose and Structure .................................................................................. 17 References ........................................................................................................................ 18
Chapter 2 Impacts on Visitor Perceptions of Soundscapes in Muir Woods National
Monument ........................................................................................................................ 33
Introduction ...................................................................................................................... 34 Methods ............................................................................................................................ 41
Analysis of the perception of the soundscape .......................................................... 48 Results .............................................................................................................................. 49 Discussion ........................................................................................................................ 52 Conclusion ....................................................................................................................... 57 References ........................................................................................................................ 58
Chapter 3 Aircraft Sound Management in Denali National Park and Preserve ....................... 71
Introduction ...................................................................................................................... 72 Literature Review ............................................................................................................. 73
Protecting Natural Sound in Parks ........................................................................... 73 Dose Response Methods .......................................................................................... 75 Indicators and Thresholds for Soundscape Quality .................................................. 77 Study Purpose ........................................................................................................... 80
Methods ............................................................................................................................ 80 Survey Location ....................................................................................................... 80 Audio Clip Dose Response Survey .......................................................................... 82
Results .............................................................................................................................. 87 Discussion ........................................................................................................................ 92
Management implications ........................................................................................ 95 Conclusion ....................................................................................................................... 96 References ........................................................................................................................ 97
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Chapter 4 Visitor Preferences for Soundscape Management in Muir Woods National
Monument ........................................................................................................................ 107
Introduction ...................................................................................................................... 108 Soundscape Management ......................................................................................... 109 Management Strategies ............................................................................................ 110 Study Justification .................................................................................................... 114 Study Site ................................................................................................................. 115 Experimental Design ................................................................................................ 116 Survey Administration ............................................................................................. 117 Choice Experiment Design ....................................................................................... 118 Model Analysis ........................................................................................................ 120
Results .............................................................................................................................. 121 Sample Profile .......................................................................................................... 121 Stated Choice Model ................................................................................................ 122 Preferences for Park Closure .................................................................................... 126
Discussion ........................................................................................................................ 127 RQ1: What tradeoffs are visitors willing to make in order to hear natural sounds
in Muir Woods National Monument? ............................................................... 127 RQ2: Are preferences different for visitors in the treatment group (signs present
asking visitors to maintain quiet) vs. the control group (all signs are
covered)? .......................................................................................................... 128 Management Implications ........................................................................................ 129
Conclusion ....................................................................................................................... 131 References ........................................................................................................................ 132
Chapter 5 Conclusion and Implications ................................................................................... 144
Summary of Findings and Implications ........................................................................... 144 Implications ...................................................................................................................... 146
Home Sound Level Influences Soundscape Perception ........................................... 147 Assessing Large Variety of Sound Levels Improves Validity of Soundscape
Thresholds ........................................................................................................ 147 Park Visitors Prefer Soundscape Management ........................................................ 148
Conclusion ....................................................................................................................... 148 Appendix A Chapter’s 2 &4 Survey Instrument ............................................................. 150 Appendix B Chapter 3 Survey Instrument ...................................................................... 166
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LIST OF FIGURES
Figure 2-1 Summary of Soundscape Elements that are comprised of sounds that are
natural (geophony), flora and fauna (biophony) and/or human-made (anthrophony) ..... 36
Figure 2-2. Estimation of sound levels and common sounds (adapted from NPS, 2008) ....... 37
Figure 2-3. The positive and negative effects natural and anthropogenic sound can have
on the wellbeing of humans. ............................................................................................ 37
Figure 2-4. Muir Woods National Monument (MUWO), the study area, is located X km
north of San Francisco, California ................................................................................... 42
Figure 2-5. Estimated soundscapes in MUWO ........................................................................ 48
Figure 2-6. Predicted daytime sound level and distribution of visitors’ home sound level
exposure ........................................................................................................................... 50
Figure 2-7. Distribution of sound level exposure .................................................................... 50
Figure 3-1. Summary of survey response for acceptability for varying sound levels .............. 85
Figure 3-2. Predicted relationship between visitor acceptability and aircraft noise level
using survey data collected at all sites (MSLC, HL, HO, and MSLC). ........................... 89
Figure 3-3. Predicted acceptability models by number of overflights (3, 9, 15, or 30
minutes per hour). Solid lines represent the predicted relationship between
acceptability and sound level ........................................................................................... 89
Figure 3-4. Predicted acceptability models by number of overflights (1, 10, 25, 50, or 100
times per day). Solid lines represent the predicted relationship between acceptability
and noise level. ................................................................................................................. 90
Figure 3-5. Predicted relationship between visitor interpretation (pleasing to annoying)
and aircraft noise level using survey data collected at all sites (MSLC, HL, HO, and
MSLC). ............................................................................................................................ 90
Figure 4-1. Map of San Francisco Area ................................................................................... 116
Figure 4-2. Educational Signs (used in treatment weeks) ........................................................ 117
Figure 4-3. MUWO Stated Choice Attributes ......................................................................... 119
Figure 4-4. Example of choice scenario................................................................................... 120
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LIST OF TABLES
Table 2-1. Details on survey questions, response values and how they relate to
understanding the visitor and sound perception. .............................................................. 44
Table 2-2 Multiple regression results for pleasantness ............................................................ 51
Table 3-1. Final GLMM models .............................................................................................. 87
Table 3-2. Observed relationship between each response variable and the model-
averaged parameters from the final models ..................................................................... 88
Table 3-3. Acceptability of hearing small aircraft sounds from recording #6 (flights per
hour) ................................................................................................................................. 91
Table 3-4. Acceptability of hearing aircraft sounds from recording #6 (times per day)
before respondent would no longer visit Denali .............................................................. 91
Table 3-5. Respondents bothered, disturbed, or annoyed by other aircraft ............................. 92
Table 4-1. Parameter Estimates for the Latent Class Model .................................................... 123
Table 4-2. Differences in marginal utility scores between the treatment and control
groups ............................................................................................................................... 124
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ACKNOWLEDGEMENTS
To be honest, this part of my dissertation has been more difficult to write than I expected.
It’s hard to put into words how grateful I am to have the two most supportive advisors, Drs. Peter
Newman and Derrick Taff. When I reflect on your mentorship, it spans more than ten years. You
both have been role models and guiding lights since my time as an undergraduate at Colorado
State. Thank you both for always having so much confidence in me. At times I was discouraged
by the challenges you threw my way, but those experiences have only strengthened my skillset, as
well as, my own self confidence. Peter, thanks for giving me the opportunity to conduct
meaningful research in parks and for always knowing when I needed a laugh or a nudge of
encouragement. It’s scary how well you know me—I thought I could hide my struggles, but you
know me all too well! Derrick, thank you for your selfless commitment to mentoring me through
the epic highs and lows of graduate school. Your guidance and advice has been invaluable! I want
to also thank both of you for making me feel like a part of your families. I admire your generous
and welcoming approach to mentorship.
I would also like to express my deep appreciation for my committee members, Drs.
Andrew Mowen and Justine Blanford. Andy, thank you for always putting time and effort toward
assisting me with either a class project, my exams, or writing my first journal article. You’ve
helped me realize my potential as a writer and researcher. Justine, thank you for your endless time
and dedication to my education. I can’t tell you how much I value your mentorship and words of
advice. To this day, when I find myself discouraged, a walk and a cup of tea help with finding a
new perspective.
I would also like to acknowledge the National Park Service Natural Sounds and Night
Skies Division and their support for social science acoustics research at Penn State. Special
thanks to Daniel Mennitt for his willingness to share data and insights. Data analysis would have
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been an extreme challenge without the help of Megan McKenna and Kurt Fristrup. I would still
be trying to figure out how to code in R if it wasn’t for Megan’s help. Your kindness and
generosity is deeply appreciated. Thank you for opening your home to me and for taking the time
to work though my data analysis with me.
I wouldn’t have gotten to this point in my education without the support of my husband,
Dr. Mike Ferguson. Thank you for being my biggest cheerleader and source of comfort. You’ve
been with me to celebrate the highs and lift me up during the lows, especially with chocolate and
coffee. Thanks for making me laugh and reminding me that this is recreation management and not
brain surgery. I think my stress levels would have been through the roof if you hadn’t been by my
side.
I would like to also thank my dear officemate and friend to the end, Jenn Newton for her
love and support. Your positive energy, intellect, and keen ability to read my mind made the
mundane grad school grind so much more enjoyable. Also, a huge high-five goes to Brian Soule
for being my best friend and roommate. Thanks for laughing with me (or at me) and dealing with
me at times when I was hangry. To the rest of the grad students, thanks for always having my
back and for making time spent both in class and out of class exciting.
I am grateful to have had funding and support from the National Park Service, as well as,
the opportunity to collaborate with accomplished researchers. Thank you to Shan Burson and
Davyvd Betchkal for having the kindness and patience to work with me on acoustics projects that
were way above my head. It has been a pleasure to conduct research in Denali National Park and
Preserve. I appreciated guidance from Denali managers Rose Keller and Dave Schirokauer.
Through the NSF project, I’ve been grateful for the opportunity to collaborate with Cal Poly and
Boise State Universities. Clinton Francis, Jesse Barber, and Mitchell Levenhagen, thank you for
your patience and encouragement…and for teaching me to play the most dangerous game I’ve
ever encountered, Stump.
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Finally, I would like to acknowledge my mom, dad, and Brother John. Thank you for
taking me to parks as a child and for showing me how to love the natural world. More
importantly thank you for your unconditional love and support. Thanks for always telling me how
proud you were of me, it was more motivating than you’ll ever know. Mom, thanks for proof
reading papers and survey instruments. You are the best proof-reader I know. Also, thanks for the
sweet care packages that always included candy and some type of stress reliever. Your coloring
books were my escape while studying for exams. I’m really lucky to have such an amazing
family.
Chapter 1
Introduction
Sound can simply be defined as a vibration that travels through a medium, most
commonly air, which is then heard by people or animals. The science of sound is studied by
multiple disciplines. Biologists and bioacustitions explore the impacts of sound on wildlife such
as birds and ocean mammals. Environmental psychologists study the impact of sound on human
cognition, emotion, and so on. Within the field of recreation management, researchers aim to
understand the impact of sound, both natural and anthropogenic, on visitor experiences in parks.
While sound is simply a vibration, noise is the negative or unwanted interpretation of sound. If
people travel to parks to enjoy the natural world, what are the outcomes of experiencing man-
made noise? This dissertation aims to explore different methodologies for measuring visitor
experiences with the acoustic environment in National Parks. The first paper explores the
relationship between one’s home sound level and their interpretation of soundscapes at Muir
Woods National Monument. The purpose of the second paper is to utilize a large suite of sound
clips to determine visitors’ threshold for propeller aircraft noise at Denali National Park and
Preserve. Finally, the third paper aims to test the tradeoffs visitors to Muir Woods National
Monument are willing to make in order to experience a more natural soundscape.
The National Park Service Organic Act (1916) established a system of protected National
Parks and outlined their objectives. The goal of the National Park Service (NPS) is twofold: to
protect resources, such as water and wildlife; and provide enjoyment for “future generations”. As
visitation to parks increases, so does anthropogenic or manmade sounds (NPS, 2000). Visitors are
traveling to parks in cars, trucks, and motorcycles. They are sightseeing in airplanes and
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helicopters. Additionally, areas within parks are becoming louder as a result of visitors talking,
using cellphones, and playing music on portable speakers. For the majority of park visitors,
hearing natural sounds is an important motivation for their park visit (Driver, Nash, & Hass,
1978; Marin, Newman, Manning, Vaske, & Stack, 2011; McDonald, Baumgartner, & Iachan,
1995). These increasing anthropogenic sounds can also impact wildlife by changing behavior and
breeding patterns (Francis & Barber, 2013). If the goal of the NPS is to protect resources and
provide enjoyment, increasing anthropogenic sounds are negating these goals. It is important for
park managers to measure and mitigate the acoustic environment or the soundscape, in order to
provide visitors with high quality experiences and benefits.
In a recent paper by Francis et al., (2017), natural sounds are described as benefits to
humans in the form of a psychological ecosystem service. The negative impacts of anthropogenic
sounds to human health and wellbeing are well documented. Prolonged exposure to these sounds
can cause hearing loss, increased stress and heart disease (Babisch, 2003). They can also reduce
cognitive function; which was found in children who attended school located in a noisy flight
path (Cohen, Evans, Krantz, & Stokols, 1980). Conversely, natural sounds can provide humans
with positive health outcomes. These recent studies have found that exposure to natural sounds
can improve cognition (Abbott, Taff, Newman, Benfield, & Mowen, 2016), mood (Benfield,
Taff, Newman, & Smyth, 2014) and recovery from stress (Alvarsson, Wiens, & Nilsson, 2010).
Based on this evidence, the benefits natural sounds provide humans are couched as an ecosystem
service. According to the Millennium Ecosystem Assessment (MA, 2005) an ecosystem service is
an entity derived from a natural ecosystem that benefits human wellbeing.
The increase in anthropogenic sounds which masks or reduces natural sounds can
influence human wellbeing through cultural or psychological ecosystem services like recreation,
aesthetic beauty, and reflection (Francis et al., 2017). Cultural ecosystem services are the non-
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tangible benefits provided by ecosystems through recreation, cognitive development, enjoying
natural beauty, enhancing spirituality and so on (MA, 2005). Whether we define natural sounds as
a cultural or psychological ecosystem service, the outcomes are similar. Measuring and
quantifying the impact of cultural ecosystem services can further justify the protection of natural
ecosystems, beyond just tangible needs like clean water (Daniel et al., 2012). For example, Fuller
et al. (2007) found that visitors to an urban park had increased measures of wellbeing when they
also perceived increased biodiversity. Planners and policy makers are beginning to recognize the
importance of ecosystem services and can use research that highlights these benefits to place
more funding and attention on protected areas that provide services (Bratman, Hamilton, & Daily,
2012).
National Parks are places where visitors can experience the benefits of the natural world,
which includes a soundscape rich in natural sounds with little interruption from man-made noise.
The purpose of this dissertation outline is to explore various methods for measuring and
managing soundscapes and their impacts to visitors. This research aims to assist managers in
maintaining natural quiet, to adhere to policy mandates, but also for the positive experiences and
benefits they provide through ecosystem services.
What is a soundscape?
A soundscape can be defined simply as the “acoustical environment” (Newman,
Manning, & Trevino, 2010, p. 2). The acoustic environment has been identified as an important
resource. Researchers from diverse disciplines study sounds and their impacts on both humans
and wildlife (Barber et al., 2011; Benfield, Taff, et al., 2014; Merchant et al., 2015; Pijanowski et
al., 2011). In the past, research on sound has focused on noise defined as unwanted sounds. A
more comprehensive approach to understanding the acoustic environment can be achieved by
4
considering soundscapes rather than just noise. In this paper, the term soundscape refers to the
relationship between a landscape and the composition of its sound (Pijanowski et al., 2011). The
field of soundscape ecology classifies the soundscape into three types: geophony, biophony, and
anthrophony (Krause, Gage, & Joo, 2011). Geophony refers to the sounds produced by the
geophysical environment, such as, wind and flowing water. Biophony is the combination of
sounds produced by non-human living organisms, like birdsong for example. Anthrophony refers
to human made noise, such as, vehicle and aircraft sounds.
The Importance of Sounds
Noise and anthropogenic sounds have been found to negatively impact both humans and
wildlife (Francis & Barber, 2013; Goines & Hagler, 2007). For humans, exposure to excessive
environmental noise can cause negative health outcomes such as stress, inadequate sleep, heart
disease and hearing loss (Hammer, Swinburn, & Neitzel, 2014). Moreover, in the United States,
millions of people are exposed to noise that exceeds the recommended level and are therefore at
risk of heart disease and other negative health outcomes (Hammer et al., 2014). For wildlife,
noise can make it more difficult to find a mate, detect prey or another predator, and like humans,
increase stress (Francis & Barber, 2013).
There is increasing evidence that postulates the negative impacts of anthropogenic sounds
to human health and wellbeing. It is well known that loud noise can damage one’s hearing.
Babisch et al. (2003) found that prolonged exposure to anthropogenic sounds can cause hearing
loss, increased stress, and even heart disease. In another study, Cohen et al. (1980), found that
children who attend school in a direct flightpath have increased stress and lower cognitive ability
than children who attend a quiet school. As our society continues to urbanize, the risk for
prolonged exposure to loud anthropogenic sounds will increase.
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While a number of studies highlight the negative impact of anthropogenic noise,
researchers are beginning to understand the positive influence of natural sounds on human health
and wellbeing (Abbott et al., 2016; Alvarsson et al., 2010; Benfield et al., 2014). The theoretical
basis for these studies come from the idea that there is a positive relationship between the natural
environment and human wellbeing. One theory is Attention Restoration Theory (ART; Kaplan,
1995) and the other is Stress Restoration Theory (SRT; Ulrich, 1991). Early studies in both ART
and SRT test the impact of viewing natural environments. Studies that test the influence of natural
sounds, test the impact of the acoustic environment. The positive impact of natural sounds is
three-fold: cognitive, physiological, and affective (Abbott et al., 2016; Alvarsson et al., 2010;
Benfield et al., 2014). These are also the benefits that fit well within the context of cultural
ecosystem services (Francis et al., 2017).
Earlier mentioned was a study by Cohen et al. (1980) that determined children who
attend school in a direct flightpath underperform on mental tasks compared to children at quiet
schools. If overflights can decrease cognitive performance, what impact can natural sound have
on cognitive performance? Berman, Jonides, & Kaplan (2010) found that study participants who
walk in a natural area perform better on tasks than those who walk in an urban area. This study
didn’t control for the acoustic environment, however, sounds could be an important variable.
Abbott et al. (2016) controlled for the acoustic environment. They found that after a mentally
exhausting task, study participants who were exposed to natural sounds, like those heard in a
National Park, outperformed those who heard no sounds. These studies provide evidence for the
positive influence of natural sound on human cognition.
Natural sounds have been found to improve recovery from stress, which is evidence of
the positive physiological impact of natural sound. For instance, Alvarsson et al. (2010)
conducted a study that tested stress recovery through heart rate and skin conductance. They gave
study participants a difficult arithmetic task, which increased stress. They exposed participants to
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either natural or anthropogenic sounds. They found, through physiological measures of stress,
that natural sounds promoted a faster stress recovery. Exposure to anthropogenic sounds
increased stress levels. Prolonged stress can lead to heart disease and other negative health
outcomes (Hammer, Swinburn, & Neitzel, 2014). Exposure to natural sounds, like those in
National Parks (if managed appropriately), can provide a place to restore from the stress of daily
life.
Finally, natural sounds can have a positive influence on affect or mood. Benfield et al.
(2014), tested how exposure to different acoustic environments effects mood. Study participants
were asked to watch a disturbing video, mood was measured through the PANAS scale. Then,
they were exposed to either natural or anthropogenic sounds. Mood was tested again and they
found that participants exposed to natural sounds had significantly improved emotional state
compared to those exposed to anthropogenic sounds. This study provides evidence for the
positive impact of natural sound on human affect.
Natural Sound and Resource Protection
Noise in National Parks is increasing. In a place where human caused environmental
impacts are kept to an absolute minimum, natural sound is becoming overshadowed by human
induced noise (Lynch, Joyce, & Fristrup, 2011). According to the U.S. National Park Service
(NPS), “noise levels in park transportation corridors today are at 1,000 times the natural level”
(p.11). National parks and wilderness areas are places where one could expect to find silence or at
least an escape from noisy urban environments. Enjoying the sounds of nature, silence and
escaping noise are often the most common motivations for parks and protected area visitors
(Driver et al, 1987; McDonald et al., 1995). With increased visitation to these areas, the amount
of unwanted sounds from traffic, airplanes, helicopters, people, etc. has become a topic of
7
concern. The NPS Soundscape Management Policy 4.9 states “the service will take action to
prevent or minimize all noise that, through frequency, magnitude, or duration, adversely affects
the natural soundscape or other park resources or values…” (NPS, 2006). National Park managers
are taking the steps to understand acceptable levels of noise and to mitigate noise so that natural
sounds are not compromised.
The National Parks Overflight Act passed in 1987, required the NPS to identify
“acceptable levels” of noise produced by overflights in parks (NPS). Aircraft noise in the Grand
Canyon National Park was examined, as it is a popular site for helicopter tours, and it was
discovered that all locations within the park were affected by noise (Mace, Bell, & Loomis,
1999). Mace, Bell, and Loomis (1999) studied the effects of helicopter noise on the visual quality
of landscapes in regard to feelings of tranquility and solitude. In this lab study, participants
viewed landscape photos of the Grand Canyon while being exposed to different sounds:
helicopter at two sound levels (40 dB(A) and 80 dB(A)) and natural sounds (wind, bird song,
babbling brooks, natural quiet). This study found that unwanted noise affected visual landscape
quality. Feelings of annoyance, solitude, and tranquility were also negatively swayed by
helicopter noise. Interestingly, the specific sound level (40 and 80 dB(A)) was unimportant, all
variables that addressed landscape perception were negatively influence by unwanted sound
regardless of level.
Designated wilderness is one of the highest levels of protection for public lands. Federal
wilderness areas are expected to provide “outstanding opportunities for solitude or a primitive
and unconfined type of recreation” (National Wilderness Preservation Act 1964, Section 2c).
Tarrant, Hass, and Manfredo (1995) evaluated the effects of overflights on visitors to wilderness
areas in Wyoming. This study used a dose exposure survey technique to gain an understanding of
how visitor characteristics influence evaluations of overflights. In this study, dose refers to the
number, proximity, and types of overflights encountered. Researchers concluded that respondents
8
had strong negative attitudes towards hearing overflights and were slightly more affected by
hearing overflights than seeing them. Levels of solitude and tranquility were also decreased by
sounds of overflights. Furthermore, respondents who had previously visited the wilderness area,
had lower tolerance and a higher negative attitude towards overflights. Because this particular
analysis did not include actual recordings of sound levels that visitors experienced, it is important
to note that their response to overflights was dependent on participants’ tolerance for noise.
Indicators and Standards of Soundscape Quality
National parks use a specific framework for managing visitor use. Visitor Experience and
Resource Protection (VERP) is the carrying capacity framework that was developed for and
applied to the NPS (Manning, 2001). More recently an adaptation of visitor management
frameworks and collaboration between federal agencies has led to a more general Visitor Use
Management Framework (Interagency Visitor Use Management Council, 2016). The framework
has been developed to guide adaptive management practices for all federal land management
agencies. The framework is comprised of several elements. These are considered elements or
components rather than steps in a process. Unlike a recipe, the VERP framework is an iterative
and ongoing process. Essentially, an interdisciplinary team develops management objectives. A
management objective is a clear management goal based on policy and the type of recreation
experience being managed for. An indicator is a measurable variable based on the identified
management goal. These variables can be biophysical (environmental impacts) or
social/experiential (crowding), depending on management objectives. A standard is defined as the
minimum acceptable level of quality based on the indicator variable. Another way of thinking of
standards is as thresholds for quality. For example, a park might manage wilderness areas for
“solitude”. So if the management objective is solitude, an indicator of this management objective
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could be number of people on the trail. A standard can be identified by asking, what is the
minimum acceptable level of people on the trail? Indicators and standards are used to identify
thresholds for quality visitor experiences. Managers can then monitor these variables to maintain
recreation quality.
Soundscape quality has been assessed, using an empirical approach to carrying capacity.
Pilcher, Newman, and Manning (2008), used the normative approach to identify indicators and
standards of a quality soundscape in Muir Woods National Monument. Indicators were identified
by having participants listen to the sounds in the park (a listening exercise). Respondents listed
the sounds heard and their evaluation of each sound (acceptable vs. unacceptable/annoying vs.
pleasing). Sounds that were deemed annoying and unacceptable were considered indicators.
Noise from other visitors (talking, screaming, etc.) was considered an indicator of quality. In
order to determine a standard, the researchers created sound clips with varying levels of visitor
noise. The sound pressure level of noise was used to measure the standard. The minimum
acceptable level of visitor noise indicated a standard. Managers went on to monitor the park
soundscape and found that sound levels exceeded the standard. Thus, management actions were
taken to quiet the park (Stack et al., 2008).
Natural Sound as an Ecosystem Service
The Millennium Ecosystem Assessment (MA; 2005) aimed to analyze the state of ecosystem
changes around the world and assess their impacts on human wellbeing. The overall results from
the assessment and research outlined in this document are grim. Worldwide, ecosystem services
are declining, which is why it is important develop plans and policies to conserve important
ecosystems. According to the MA (2005) an ecosystem service is something derived from a
natural ecosystem that benefits human wellbeing. An example of an ecosystem service is clean
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air, because it allows for humans to breathe and not ingest harmful pollutants. Ecosystems are
natural systems comprised of plants, soil, wildlife, people, and microorganisms. The MA (2005)
defines 4 types of ecosystem services: (1) provisioning services like food and timber; (2)
regulating services like water quality, flood control, and climate; (3) cultural services like
recreation, aesthetic beauty, and spirituality; and (4) supporting services like nutrient cycling.
These are all ecosystem services that provide benefits to wellbeing.
The framework described by the MA (2005) is used for measuring and assessing
ecosystem services. There are three elements in the framework: (1) a change in divers that impact
biodiversity like increased population; (2) this leads to a change in biodiversity; (3) this leads to a
change in ecosystem services and the benefits they provide to human wellbeing. This framework
can occur across multiple scales (national and regional). Under this framework, natural sounds
can be influenced by changes in biodiversity, which are a result of development and increased
anthropogenic sounds. Sounds are a common pool resource. Once they are taken from the shared
natural system, they are difficult to replace. The increase in anthropogenic sounds and reduction
in natural sounds can influence human wellbeing through cultural ecosystem services like
recreation, aesthetic beauty, and reflection. The following papers with expand on this framework.
Cultural ecosystem services are the non-tangible benefits provided by ecosystems
through recreation, cognitive development, enjoying natural beauty, enhancing spirituality and so
on (MA, 2005). Miclu et al. (2013) conducted an extensive literature review of research related to
cultural ecosystem services. They found that the research was conducted by multiple different
disciplines and that the approach to cultural ecosystem services is diverse. Miclu et al. (2013)
note that cultural ecosystem services are subjective based on both individual and societal and
cultural differences. Additionally, this type of ecosystem service is often not associated with an
economic benefit (like housing value). Ultimately, there is a lack of consensus regarding this type
of ecosystem service. In their review they found that some papers claim a monetary value for
11
cultural ecosystem services (CES), while others argue against placing a monetary valuation on
them. Over half of the papers they reviewed addressed some kind of assessment related to CES
and mental wellbeing.
Researchers have developed tools for measuring the outcomes of land management
strategies on ecosystem services. For example, Goldstien et al. (2012) and Nelson et al. (2009)
use a GIS modeling software called INVEST to model various outcomes of different land use
scenarios. This software can account for CES, however in these examples they are focused on the
outcomes of development and conservation on provisioning and supporting ecosystem services.
The software can analyze both biophysical and monetary outcomes. Plieninger et al. (2010) argue
that it is difficult to assess biophysical and monetary values of CES and they need to be evaluated
for socio-cultural benefits. They measure the attitudes, beliefs and behaviors related to ecosystem
services. In their study, they asked participants to conduct a participatory mapping exercise of
their home village. They marked areas on the maps where they acquired CES like recreation,
spiritual, and aesthetic benefits. The researcher used autocorrelation spatial analysis techniques to
assess patterns related to CES.
In a recent paper, Bratman et al. (2016) coins the term, psychological ecosystem services.
This paper highlights the research and theory related to the positive relationship between humans
and natural environments. They discuss Biophilia, SRT and ART. They argue that the natural
world provides humans with positive mental outcomes like cognitive and stress recovery, which
should be considered a psychological ecosystem service. The paper postulates that valuating the
benefits of psychological ecosystem services will aid in persuading policy makers and planners to
place more funding in areas like park and garden development, places where people can gain the
benefits of psychological ecosystem services.
Natural sounds provide humans with improved wellbeing. Earlier this paper discussed the
positive influence of natural sound on cognition, physiology, and affect. Based on the definition
12
of an ecosystem service, natural sounds are absolutely a benefit to human health and wellbeing,
provided by the natural environment. I argue that natural sounds can fit under the umbrella of
both CES and psychological ecosystem services (PES). Natural sounds are an important part of
the recreation experience, a benefit of CES. As mentioned earlier, they are a significant
motivation for park visitors. I would argue that hearing natural sounds is one of the many benefits
of recreating outdoors. Natural sounds can also influence one’s aesthetic experience in the
outdoors. Wienzimmer et al. (2014), found that anthropogenic sounds decrease visitors’
assessment of the naturalness of a park view scape. Natural sounds are also non-material and
intangible benefits described by the definition of CES (Miclu et al., 2013).
The positive benefits of natural sound on improving stress, cognition, and mood, fit well
within the definition of a PES (Bratman et al., 2016). In Bratman et al.’s (2016) review of
literature related to the benefits of nature and mental health, they point out that most studies
compare a natural environment to a non-natural environment. The common denominator in the
natural environments tested in these studies is quiet. Natural quiet and sounds of nature are an
important aspect of natural ecosystems. They provided humans with mental benefits, like
restoration. Whether we choose to define natural sounds as a CES or PES, the main goal is to
continue to study their benefits.
Methods Used in Natural Resource Management
Stated Choice Modeling.
Stated choice modeling was initially used in market research to understand preferences in
product design (Louviere, Hensher, & Swait, 2000). This method is used to help researchers
understand how people evaluate choices and the tradeoffs they are willing to make in order to
13
obtain an ideal scenario. Respondents of stated choice surveys are asked to make a series of
distinct choices between two scenarios that have multiple levels of attributes. For example, when
buying a new car, one has the option of choosing from an overwhelming number of accessories
(i.e. leather interior, power windows, satellite radio, etc.). The method of stated choice modeling
can tell us about the types of choices and “trade-offs” a sample of consumers might make. These
results aid in more precise product development and manufacturing.
This method has also been applied to park and recreation management (Bullock &
Lawson, 2008; Newman, Manning, Dennis, & Mckonly, 2005; Pettebone et al., 2011). Rather
than measuring preferences for products, stated choice has been used to measure visitors’
preferences and tradeoffs for social, natural, and managerial experiences in parks. Newman et al.,
(2005) studied the tradeoffs of backcountry users in Yosemite National Park’s wilderness areas.
This study used a survey with paired comparisons to determine respondents rated signs of human
use at backcountry campsites to be an important indicator of quality. Moreover, this method
allowed for researchers to provide Yosemite National Park management with the results of the
model, which indicated that respondents were willing to deal with more stringent management in
order to gain quality in the appearance of campsites.
In another study, Bullock and Lawson (2008), used stated choice to understand visitor
preferences for management at Cadillac Mountain, in Acadia National Park. Attributes for
management conditions included varying levels of management interference, ranging from
freedom and open access to turning many visitors away from visiting the summit during busy
times. The study also included attributes for social conditions (the number of people on the trail)
and resource conditions that reflected varying levels of visitor caused environmental damage.
During data collection, respondents were presented scenarios that described a narrative of varying
attributes, as well as, a photo that portrays the attribute narrative. Results from this study
identified visitors’ preference towards protecting the environmental resources on the summit.
14
Additionally, they are in favor of rigorous management implications, but prefer the summit to be
open access. These findings allow for management to understand the specific preferences of
visitors to this iconic park summit.
Researchers have also used stated choice modeling to understand park visitor preferences
off the trail. Pettebone et al. (2011) used this method to investigate visitors’ preference for
traveling within the Bear Lake Road area of Rocky Mountain National Park. Due to increased
use, the NPS is using alternative transportation, like bus systems, to move visitors through parks.
This study analyzed varying attributes related to destination convenience, traffic and visitor
volume, and number of hikers on a trail. Photos were also utilized to depict different scenarios.
Results from this study found that visitors prefer to use their personal vehicles in the park. They
were willing to tradeoff using their personal vehicle and use the bus transportation to avoid
congestion on the roads and trails. These data were useful to managers who can then use this
information to design a transportation system and encourage visitors to use the bus rather than
deal with vehicle traffic.
Mapping soundscapes.
Noise maps have been developed using the measurement of sound levels produced by
traffic and other noise, incorporated with modeling techniques. In these models, sound levels
from a source are identified and outputs are predicted based on varying geospatial data like
elevation, as well as, physical elements of sound propagation. Noise maps that illustrate sound
propagation in a natural environment have used different methods for noise modeling. A GIS tool
called SPreAD-GIS (The Wilderness Society, San Francisco, CA) integrates data on topography,
land cover, and weather to predict sound events (Reed, Boggs, & Mann, 2012; Reed, Ph, Smith,
Boggs, & Mann, 2010). Researchers used this tool to map the potential noise impacts from oil
15
and gas compressors (Barber et al., 2011). Other noise modeling programs exist, such as, NMSim
(Wyle Laboratories, Inc., Arlington, VA) can be used to map the effects of overflights (Barber et
al., 2011; Plotkin, 2001). Another noise modeling program, CadnaA (DataKustik, Greifenberg,
Germany) is used for calculating and visualizing propagation of anthropogenic noise from roads,
railways, and aircraft. Previous studies have used it to model hikers exposure to transportation
noise (Park, Lawson, Kaliski, Newman, & Gibson, 2010) and the noise impacts of vehicles in
Glacier National Park (Barber et al., 2011).
Noise modeling methods are sufficient for predicting sound from powerful sources like
traffic or aircraft at specific locations. However, according to Mennitt et al. (2014), these methods
are impractical for mapping natural environments because of the unspecified number of sound
sources and their random spatial dispersion. Different from noise modeling software, a geospatial
modeling method was used to predict ambient sound pressure levels across the contiguous United
States (D. Mennitt et al., 2014). This method utilized 69 potential explanatory variables derived
from spatial data from categories such as climate, hydrology, land cover, etc. The predictive
strength of explanatory variables were derived using sound level measurements from 190
National Parks across the country. This method is useful in predicting the acoustic environment
on national and regional scales.
Within the context of natural resource management, researchers have used acoustic mapping
to estimate the effects of noise on both wildlife and park visitors. For example, researchers used a
sound propagation map to modeling mapping hikers’ exposure to transportation noise within the
Bear Lake corridor of Rocky Mountain National Park (Lawson, Kaliski, Newman, & Gibson,
2009). In another study, researchers determined that noise produced by snowmobiles impacted
vegetation cover, wilderness experience, and the spatial behavior of moose (Mullet, 2014).
16
Management Strategies
When extensive visitor use begins to degrade the quality of park resources, managers
use different strategies to improve or protect resources. Direct and indirect management
strategies are used to change visitors’ perceptions or behaviors towards resource
protection (Manning, 2011). Direct management strategies apply regulatory measures to
change visitor behavior, while indirect strategies aim to impact visitors’ decision-making
process to influence behavior (Manning, 2011). An example of a direct management
strategy would be closing a degraded area within a park. For example, Hockett, Marion,
& Leung, (2017), used various management techniques, including trail closure, to reduce
off-trail hiking at a highly visited urban park. Informational or educational signs are a
form of indirect management that can alter visitor attitudes or perceptions (Manning,
2003). In relation to managing soundscapes, indirect management, in the form of
educational signs have been studied (Stack et al., 2011; Taff et al., 2014). Stack et al.
(2011), found educational signs to be effective in lowering park sound levels and Taff et
al., (2014), used messaging in Sequoia National Park to improve visitors’ acceptability of
military aircraft noise. The results of these studies suggest that indirect management is
useful for shifting visitor behavior and perceptions of park soundscapes.
Summary
Overall this chapter provided an overview of theories, methodologies, and concepts
related to soundscapes, especially within the context of National Park management. It explored
17
the definition of soundscapes, the importance of natural sounds and wellbeing, natural sound as a
natural resource and the impacts of sound on the recreation experience. Moreover, ecosystem
services are defined and natural sounds are couched as a psychological ecosystem service.
Finally, the review examined stated choice modeling and acoustic mapping methods.
Dissertation Purpose and Structure
The purpose of this dissertation is to explore strategies for measuring and
managing the impacts of noise as it relates to human experience and ecosystem services. Chapter
one introduces the state of soundscapes research in terms of measurement and theory. Chapters 2
through 4 were written as stand-alone manuscripts that will later be submitted to relevant peer-
reviewed journals. Chapter 2 aims to understand the relationship between park visitors’ home
sound exposure in relation to their rating of the soundscape at Muir Woods National monument.
Chapter 3 utilized an innovative method for determining visitor thresholds for propeller aircraft
noise in Denali National Park and Preserve. Chapter 5 assessed visitor preferences for soundscape
management at Muir Woods National Monument. The 5th chapter summarizes the combined
results of the three dissertation studies. The following chapters aim to answer these six research
questions:
Chapter 2: Impacts on Visitor Perceptions of Soundscapes in Muir Woods National
Monument
1) What factors influence visitors’ perception of the soundscape in Muir Woods
National Monument?
2) How does the sound level of visitors’ home zip code area influence their park
soundscape perception?
18
Chapter 3: Aircraft Sound Management in Denali National Park and Preserve
3) How can researchers best inform the development of thresholds for
soundscape quality using dose response methodology?
4) What factors influence visitors’ perception of overflight audio clips?
Chapter 4: Visitor Preferences for Soundscape Management in Muir Woods
National Monument
5) What tradeoffs are visitors willing to make in order to hear natural sounds in
Muir Woods National Monument?
6) Are preferences different for visitors in a treatment group (signs present
asking visitors to maintain quiet) vs. a control group (all signs are covered)?
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33
Chapter 2 Impacts on Visitor Perceptions of Soundscapes in Muir Woods National
Monument
Chapter 2 was written as a stand-alone manuscript that will later be modified for
submission to a peer-reviewed journal. This article seeks to answer:
Q1: What factors influence visitors’ perception of the soundscape in Muir Woods
National Monument?
Q2: How does the sound level of visitors’ home zip code area influence their park
soundscape perception?
Abstract: Unwanted sounds from man-made sources, defined as noise, are rising both in
our home environments as well as in our Natural Parks. Noise pollution can affect the
health and welfare of many mammals, including humans. As a result, National Parks aim
to protect, maintain and restore natural sounds for the health and wellbeing of wildlife, as
well as visitor experiences. For most visitors hearing the sounds of nature and
experiencing natural quiet are important motivations. Ensuring that visitors obtain these
benefits they expect are important. However, each individual has a unique perception of
their soundscape that can be influenced by a variety of factors such as their motivation
for visiting the park or personal norms and attitudes related to specific sound sources.
These in turn influences how one perceives sounds heard in a park setting. The purpose
of this study is to better understand soundscape perceptions in parks and identify how
different factors may influence these perceptions. Data on visitors’ perceptions of the
soundscape when visiting Muir Woods, north of San Francisco, were collected during
May 2016 and compared to the sounds of their home environments. A linear multiple
34
regression model was applied to the data and showed that visitors who came from noisier
zip codes perceived the park to be less pleasant. Through a better understanding of how
personal factors might influence a visitors’ perspective of a soundscape, findings from
this study can help park managers manage visitor experiences and expectations.
Introduction
Humans have the ability to close their eyes, but are never able to close their ears.
In urban areas, noise from traffic, overflights, construction, and other man-made sounds
are potentially inescapable at all hours of the day. In fact, more than eighty percent of the
contiguous United States has elevated sound pressure levels caused by noise (Mennitt,
Fristrup, Sherrill, & Nelson, 2013). Extensive exposure to noise can negatively affect
human health by elevating blood pressure levels and promoting stress and heart disease
(Goines & Hagler, 2007; Hammer et al., 2014). Parks and protected areas serve as places
where visitors can find refuge from everyday noise, however, a recent study found that
63% of protected areas experience elevated man-made noise (Buxton et al., 2017). Thus,
protecting natural sounds in parks is important, especially as visitors to parks and
protected areas are seeking natural sound experiences as a sanctuary from potentially
loud and noisy soundscapes they might experience at home.
Humans have an innate biological association to the natural world (Wilson, 1984)
that is also of value for healing the mind and body as captured by famous nature writers
such as Muir (1901; 1979) and Thoreau (1854), as well as, documented by many
researchers across disciplines (Abbott, Taff, Newman, Benfield, & Mowen, 2016;
35
Benfield, Taff, Newman, & Smyth, 2014; Ulrich, 1993; Wilson, 2001). The positive
relationship between human health and spending time in nature can promote improved
memory retention (Holden and Mercer, 2014) and overall psychological wellbeing. For
example, Attention Restoration Theory suggests the natural environment can facilitate
recovery from mental fatigue (Kaplan, 1995) while Stress Restoration Theory, posits
natures’ effect on restoring emotional and physiological responses to stress (Ulrich, 1984)
and lead to a reduction in repetitive negative thoughts (Bratman, Hamilton, Hahn, Daily,
& Gross, 2015). The main focus of these studies was on the visual elements that
environments provided, however, environments are multi-dimensional and also
comprised of soundscapes.
A soundscape can be defined simply as the “acoustical environment” (Newman,
Manning, & Trevino, 2009, p. 2) that is the relationship between a landscape and the
composition of its sound (Pijanowski et al., 2011). Soundscapes can be comprised of
three types: geophony, biophony, and anthrophony (Figure 2-1; Krause, Gage, & Joo,
2011). Geophony refers to the sounds produced by the geophysical environment, such as
wind and flowing water; biophony is a combination of sounds produced by non-human
living organisms, such as birds, wild animals, frogs and insects; and anthrophony refers
to human made noises that include talking, vehicle and aircraft sounds.
36
Figure 2-1 Summary of Soundscape Elements that are comprised of sounds that are natural
(geophony), flora and fauna (biophony) and/or human-made (anthrophony)
Noise and anthropogenic sounds can negatively impact both humans and wildlife
(Francis & Barber, 2013; Goines & Hagler, 2007). Excessive exposure to environmental
noise can cause negative health outcomes such as stress, inadequate sleep, heart disease
and hearing loss in humans (Hammer et al., 2014) (Figure 2-3). Prolonged exposure to
noise levels above 75 dB(A) have the ability to damage the inner ear and cause hearing
loss (See Figure 2-2; reviewed in Hammer et al., 2014). In fact, Hammer et al. (2014),
estimate that a large portion of U.S. residents are subject to higher levels of noise and
therefore subject to noise-related health problems. For wildlife negative effects of noise
may include difficulty in finding a mate, detecting prey or predators, as well as, increased
stress (Francis & Barber, 2013).
Geophony
- Wind
- Water
- Trees blowing in the wind
Biophony
- Birdsong
- Elk Bugal
-Small mammals
Anthrophony
- Overflights
- Traffic
- Human voices
37
Figure 2-2. Estimation of sound levels and common sounds (adapted from NPS, 2008)
Figure 2-3. The positive and negative effects natural and anthropogenic sound can have on the
wellbeing of humans.
38
Just as viewing built environments fail to contribute to psychological wellbeing,
exposure to anthropogenic sounds impede positive health outcomes. Urban soundscape
sources such as aircraft, traffic, and people talking have been found to interfere with
memory (Benfield et al., 2010) and assessments of landscape beauty (Weinzimmer et al.,
2014). Additionally, Cohen et al. (1980), found that children who attend school in a direct
flightpath have increased stress and lower cognitive ability than children who attend a
quiet school. As our society continues to urbanize, the risk for prolonged exposure to
loud anthropogenic sounds will rise.
The negative impacts related to urban noise exposure paint a grim picture,
however, researchers have also focused on highlighting the positive benefits of exposure
to natural sounds. Natural soundscapes including biophony, such as birdsong; and
geophony, such as wind and running water. These sounds are important resources to the
health and well-being of both humans and wildlife (Francis et al., 2017). Natural sounds
have been found to improve human cognition (Abbott et al., 2016), enhance positive
moods (Benfield et al., 2014), and increase recovery from stress (Alvarsson et al., 2010)
(Figure 2). For wildlife, natural sounds play an important role in reproduction and safety
and the detection of prey (Francis et al., 2017).
The relationship between humans and soundscapes is complex. Smith &
Pijanowski (2014), presented a framework for better understanding this relationship that
employs methods from health, psychology, economics, and anthropology. By better
understanding the impacts of anthropogenic sounds on various elements of human
existence, researchers can provide empirical evidence that drives changes in management
and policy for protecting natural soundscapes. One example from this framework is the
39
impact of anthropogenic noise on housing value. Several studies have shown that
increased levels of transportation or other forms of man-made noise decrease housing
values (Baranzini, Ramirez, Schaerer, & Thalmann, 2008; Theebe, 2004; Trojanek,
Tanas, Raslanas, & Banaitis, 2017). Additionally, the presence of bird diversity correlates
with higher housing values. This suggests that natural sound, in the form of birdsong, can
also influence economic drivers like housing value.
To understand the complexity of soundscapes, geospatial tools and analyses that
visually represent acoustic environments are increasingly being used to understand
landscapes and capture noise from unwanted sound sources such a traffic or construction.
Visual representations of the acoustic environment have been used to demonstrate the
distribution of computed sound pressure levels in a specific area (Hong & Jeon, 2014).
These maps are useful for depicting sound pressure levels and the dispersion of these
sounds through the landscape from its source. For example, researchers developed noise
maps in Seol, Korea to predict the noise impact from new building development (Lee,
Chang, & Park, 2008). At a much larger scale, a noise map was used to estimate the
extent of transportation noise across the United States (N. Miller, 2003).
Geospatial modeling has been used to create maps that measure natural sound
levels and the impact of anthropogenic sounds throughout the contiguous United States
(Mennitt et al., 2013). These models that predict sounds across the country have also
been used recently to understand the amount of noise pollution prevalent in protected
areas (Buxton et al., 2017) and racial, ethnic, and social inequalities in relation to noise
pollution (Casey et al., 2017). Although soundscape maps integrate information collected
through a variety of devices (e.g. (Mennitt et al., 2013), a more holistic approach to
40
understanding the acoustic environment can also include human perception of sound
where people rate sounds (Aletta & Kang, 2015; Hong & Jeon, 2014; Brown, 2012) that
capture not only anthropogenic noise, but sounds from sources such as birds, water, and
wind (Aletta & Kang, 2015; Chew & Wu, 2016; Hong & Jeon, 2014; Brown, 2012).
Noise maps are used to measure exposure, as well as, identify problem areas where
mitigation is needed (Aletta & Kang, 2015; Brown, 2012) and have been useful for
developing policies that aim to regulate and manage noise (Murphy & King, 2010) so as
to minimize negative impacts (Aletta & Kang, 2015; Cai, Zou, Xie, & Ma, 2015; Hong &
Jeon, 2014; Lee et al., 2008; Liu, Kang, Luo, Behm, & Coppack, 2013; Shavelson, 2004)
Within the context of natural resource management, acoustic mapping has been
used to estimate the effects of noise on both wildlife and park visitors. These have
included sound propagation maps to model hikers’ exposure to transportation noise
within the Bear Lake corridor of Rocky Mountain National Park (Park, Lawson, Kaliski,
Newman, & Gibson, 2010) and the impact of vegetation cover on noise produced by
snowmobiles wilderness experience and the spatial behavior of moose (Mullet, 2014).
For most visitors to parks and protected areas, hearing the sounds of nature and
experiencing natural quiet are important motivations for their visit (Haas & Wakefield,
1998). As visitation to these iconic parks increase, so do sounds from transportation and
other visitors. Unwanted sounds from man-made sources, defined as noise, are increasing
in National Parks (NPS, 2010). As a result, National Parks have plans and polices in
place to protect, maintain and restore natural sounds (e.g. the Director’s Order #47,
Soundscape Preservation and Noise Management, 2000) and quiet for both visitor
experiences and wildlife health and wellbeing.
41
Several studies have explored factors that influence perceptions of soundscapes
(Axelsson, Nilsson, & Berglund, 2010; Benfield, Nurse, et al., 2014; Cottrell & Meisel,
2003; De Coensel & Botteldooren, 2007; Marin et al., 2011; Schomer, Mestre, Schulte-
Fortkamp, & Boyle, 2013). A previous study found that motivations can influence
visitors’ perceptions of the soundscape (Marin et al., 2011). Within the environmental
noise literature, it has been concluded that people in different communities perceive
identical sounds to be either less annoying or more annoying based on their personal
norms and attitudes (Schomer et al., 2013).
Based on previous studies, motivations (Marin et al., 2011) and noise sensitivity
(Benfield et al., 2014) can predict visitors’ perceptions of the soundscape they experience
in National Parks. To date, no study has explored the role of visitors’ home sound
exposure in predicting their attitude towards the park soundscape. Therefore, the research
questions related to this study are: What factors influence visitors’ perception of the
soundscape in Muir Woods National Monument? And how does the sound level of
visitors’ home zip code area influence their park soundscape perception?
Methods
Study Area
Muir Woods National Monument (MUWO) is located north of San Francisco,
California (See Figure 2-4). MUWO is a popular destination for tourists and includes 500
acres of redwood trees, with hiking trails throughout. Visitation to the park has been
steadily increasing and exceeds one million visits per year (NPS, 2017). Due to the high
42
visitation rates at this relatively small park, reservations are now required for all personal
vehicles and shuttle riders visiting MUWO. People are drawn to this park to experience
the towering and awe inspiring old growth coastal redwood forest. MUWO is keen on
protecting its natural sounds and since 2005, the park has supported a variety of
soundscape studies (Marin et al., 2011; E. Pilcher, 2006; Stack, Peter, Manning, &
Fristrup, 2011) that examined the effectiveness of signage to reduce visitor noise (Stack
et al., 2011). Due to the findings from this study the park now has a “quiet zone” in the
Cathedral Grove area of the park.
Figure 2-4. Muir Woods National Monument (MUWO), the study area, is located X km north of
San Francisco, California
43
Survey Data
A total of 537 surveys were collected between May 9th and 21st, 2016 as visitors
were exiting the park. The primary purpose of the survey was to collect information
about how noise influences visitors’ soundscape experiences. Similar to Stack et al.’s
(2011) study, the survey evaluated the effectiveness of realistic management solutions to
improving environmental conditions for wildlife and visitor experiences in Muir Woods
National Monument (MUWO). In addition, data were also collected to examine what
visitors were willing to tradeoff to achieve a high quality acoustic experience. For the
purpose of this paper, we focused on questions specific to visitors’ perceptions of the
soundscape in MUWO that capture pleasantness, noise sensitivity and ability to hear
natural sounds (Table 2-1). In addition, visitors were asked about their motivation for
visiting the park from one to six with one being “not relevant” and six being “extremely
important” and where they came from, by including a zip code. This was examined to
better understand the purpose of the visit and distance traveled.
44
Table 2-1. Details on survey questions, response values and how they relate to understanding the
visitor and sound perception.
Question Value Range
Motivation Please rate the importance of each of the
following reasons for your visit to Muir
Woods National Monument today.
1 (not relevant)
6 (extremely important)
Geographic
location
What is your home zip code? Enter zip code
Perceptions of the soundscape
Pleasantness Visitors hear a lot of sounds, including
natural sounds and human-made sounds.
Based on your experiences today, how
would you rate your pleasantness of the
soundscape?
1 (very unpleasant)
6 (very pleasant)
Noise
sensitivity
scale
1) I am sensitive to noise
2) I find it hard to relax in a place that’s
noisy.
3) I get mad at people who make noise that
keeps me from falling asleep or getting
work done.
4) I get annoyed when my neighbors are
noisy.
I get used to most noises without much
difficulty (reverse coded).
1 (strongly disagree)
6 (strongly agree)
Ability to
hear natural
sounds
Based on your experience today, how well
were you able to hear natural sounds?
1 (almost always clearly
without interference
from human-made
sound)
5 (almost always with
interference from
human-made sounds)
Pleasantness - In most park-related soundscape studies, visitors are asked to rate
the acceptability of the soundscape, as well as, their interpretation of the soundscape (a
scale from pleasing to annoying) (Marin et al., 2011; Stack et al., 2011; Taff et al., 2014).
Together these questions are measuring individuals’ perceptions and attitudes towards the
soundscape. For this study, we wanted to test a broader scale that incorporates a positive,
45
well understood attitude towards sound, referred to as pleasantness (Schomer et al., 2013)
which has been found to be an important indicator in measuring the rural soundscape (De
Coensel & Botteldooren, 2007). A review of factors related to soundscape analysis
determined pleasantness to be a commonly used and significant factor in measuring
soundscape loudness (De Coensel & Botteldooren, 2007). In the current study,
pleasantness was measured on a six-point scale from very unpleasant (1) to very pleasant
(6).
Noise Sensitivity Scale- A shortened field version of the Noise Sensitivity Scale
(NSS) was used to measure individuals’ unique perception of unwanted sounds (Benfield,
Nurse, et al., 2014). The way in which humans react to different sound stimuli is variable.
The purpose of using this measure is to better understand an individuals’ perceptions of
sounds. An example of individual difference in sound perception was found in military
veterans and their response to the loud explosive sounds associated with New Year’s eve,
which elicit a response similar to sounds heard in combat (Chemtob, Roitblat, Hamada,
Carlson, & Twentyman, 1988). Within the context of measuring sound impacts in parks,
NSS has been highly correlated with motivations and acceptability of sounds (Benfield et
al., 2014). The score from the NSS was calculated after reverse coding one of the items,
“I get used to most noises without much difficulty”, to create an overall noise sensitivity
score for each respondent. Values ranged between 2.8 and 6, where lower values indicate
low sensitivity and higher values indicate increased sensitivity to noise.
Ability to hear natural sounds - This measure was developed by the research
team to investigate respondents’ self-report of how often natural sounds were masked by
anthropogenic sounds. For analysis purposes the responses were coded numerically with
46
one being “almost always clearly without interference from human-made sound” and five
being “almost always with interference from human-made sounds”. The higher the value,
the more interference from human-made sounds the respondent reported experiencing.
Spatial Data
Average daytime sound level data for the United States as described by (Mennitt
et al, 2013) was obtained from the National Park Service. In summary, sound data was
collected over 25 days or longer from 319 sites within NP boundaries and 28 cities; for
areas that were not measured, 109 unique variables were used to predict sound levels at
those locations. Variables included climate, population density, land use, land cover,
distance from railways, airports and roads, etc. Sound pressure levels are shown as A-
weighted L50 dBA (Mennitt et al, 2013) which captures sound pressure levels based on
human hearing, and L50 represents the median sound pressure level (or the sound pressure
level present at least 50% of the time) (Austin Noise, 2009).
Zip code boundaries were obtained from the United State Census data in 2015.
All analyses were performed using ArcMap 10.4 (ESRI, 2011).
Analysis of visitors and their home sound environments
To estimate visitors’ average sound level exposure by zip code, the “zonal
statistics by table” tool was used to create output tables. The first step in this process was
creating a data table that only contained data from zip codes that matched the zip code
boundary shapefile. Initially we had zip code data from 441 survey respondents, 372 zip
codes matched with the boundary shapefile. It’s likely that some of the zip codes had
been entered incorrectly by the survey administrator and that the boundary map didn’t
contain all the potential zip codes within the United States. After a shapefile was created
47
that only contained zip code data from respondents that matched with the boundary
shapefile, the “zonal statistics by table” tool was used for each of the raster data files.
These tables were then exported and added to the existing SPSS data files containing
survey responses.
Soundscape of MUWO
Currently no map exists that captures the potential soundscape of MUWO. To
capture the different soundscapes that visitors were exposed to throughout the park a
soundscape of the park was created to capture geophony, biophony and anthrophony
(Figure 2-5). A 1000 ft. buffer around nearby highways and a 500 ft. buffer around park
roads estimates the impact of noise created by vehicle transportation. Buffer distances
were estimated based on a study that modeled noise impacts in protected areas (Barber et
al., 2011). The sound impacts from park streams were estimated by using a 100 ft.
buffer. Noise from visitors on the trail were estimated by creating a 20 ft. buffer on
hiking trails.
48
Figure 2-5. Estimated soundscapes in MUWO
Analysis of the perception of the soundscape
Multiple linear regression tests were performed in SPSS to analyze the potential
relationships between mean sound levels and soundscape perception variables.
Respondents’ rating of the pleasantness of the soundscape was used as the dependent
variable while the mean daytime sound level of home zip code, noise sensitivity, and
ability to hear natural sounds were treated as independent variables. N=372.
49
Results
During May 2016, we collected 537 surveys with a total response rate of 55%.
This response rate is low for intercept surveys in National Parks, but it is similar to other
studies that have been conducted in Muir Woods (Marin et al., 2011; Stack et al., 2011).
Within the sample, 441 respondents reported a zip code within the United States, 83 of
those identified themselves as international. Of the 441 zip codes that were provided, 372
(n=372) matched with zip codes analyzed using the 2015 Census dataset (Figure 4). For
this study, only survey data related to the 372 matched survey participants were analyzed.
Visitors came from 46 different states. The majority of visitors in our sample came from
California (30%). Twelve percent of the population were from nearby large urban areas
such as San Francisco or Oakland. Moreover, a significant portion of the sample reported
being from an urban area (77%), while the other 23% were from rural locations. Almost
half of the sample (48%) reported living 4,000 miles or more from the park and 20% of
the sample live 100 miles or less from the park. Only 6 respondents lived 10 miles or less
from MUWO.
Figure 2-6 shows the distribution of respondents and the average daytime sound
level across the contiguous United States. The minimum mean sound level of
respondents’ zip codes was 30.96 dBA and the maximum mean was 57.03 dBA. On
average, the mean sound level for respondents’ zip codes was 46.86 dBA (Figure 2-7).
Motivations for visiting Muir Woods ranged from “experiencing wildlife in
nature” to “seeing the redwoods” (ranked as the top motivation with an average rating of
5.58 out of 6). The third most important motivation for visiting the park was “to enjoy the
50
natural quiet and sounds of nature”, with an average rating of 5.07. For most of the
sample, hearing quiet and sounds of nature were very important to their visit.
Figure 2-6. Predicted daytime sound level and distribution of visitors’ home sound level exposure
Figure 2-7. Distribution of sound level exposure
12%
63%
24%
Low (<39 dBA) Medium (40-49 dBA) High (50 + dBA)
Visitors Sound Level Exposure
51
Perception of MUWO soundscape
Multiple regression models were analyzed with results from the average daytime
sound level, average nighttime sound level, average natural sounds, and average
anthropogenic sounds. The most parsimonious model used the average daytime sound
level raster data and are presented in this section. Table 2-2 shows results from the
correlation and regression analysis for the relationships of the independent variables
(average daytime sound level based on zip code, noise sensitivity and ability to hear
natural sounds) on the dependent variable, pleasantness of the soundscape (n=372).
Table 2-2 Multiple regression results for pleasantness
Independent variables
Bivariate
Correlati
ons
b-
values Beta
Partial
Correlations
Part
Correlations
Mean Sound Level -.110* -.020* -
.101 -.112 -.100
Noise Sensitivity -.132** -.130** -
.132 -.147 -.131
Ability to Hear Natural
Sound -.439***
.413**
*
-
.430 -.436 -.429
Constant 7.686
Multiple R .466***
Adjusted R-Square .217
* Significant .05 (2-tailed)
** Significant .01 (2-tailed)
*** Significant .001 (2-tailed)
Score based 5 items: 1=low sensitivity, 6=extreme sensitivity
Scale: 1=clearly without interference from human made sounds, 6=always with
interference from human made sounds.
52
Results from a correlation analysis show significant negative correlational
relationships between the independent variables and the dependent variable. The overall
regression model is significant (p<.001). Approximately 22% of the variation in visitors’
perception of the pleasantness of the soundscape is explained by the combined linear
effects of mean average daytime sound level (DTL) by zip code, noise sensitivity, and the
ability to hear natural sounds in the park. Because ability to hear natural sound has the
largest beta coefficient, we can conclude that it has a strongest net relationship with
pleasantness of the soundscape.
Discussion
Q1: What factors influence visitors’ perception of the soundscape in Muir Woods
National Monument?
Findings from this study suggest that a combination of different factors influence
visitors’ perception of the pleasantness of the soundscape in a park context. Results from
the survey revealed the sample population was highly motivated to enjoy the natural quiet
and sounds of nature. According to Schomer et al. (2013) individual perception of the
soundscape is a combination of hearing the physical sound and cognitive assimilation.
Results from this study show factors related to soundscape perception include: the ability
to hear natural sounds during the park visit, sensitivity to noise, and the average sound
level of the respondents’ home zip code. Several studies have explored factors that
influence perceptions of soundscapes (Axelsson et al., 2010; Benfield, Nurse, et al., 2014;
53
Cottrell & Meisel, 2003; De Coensel & Botteldooren, 2007; Marin et al., 2011; Schomer
et al., 2013). A previous study found that motivations can influence visitors’ perceptions
of the soundscape (Marin et al., 2011).
Ability to hear natural sounds was the strongest predictor in the model. According
to results from the bivariate correlations this was a negative relationship, so as the
interference with natural sounds increased, the perception of soundscape pleasantness
decreased. Based on previous measures of the MWUO soundscape, visitors talking is the
most prevalent anthropogenic sound and has the potential to mask natural sounds (Stack
et al., 2011). In a lab study, Benfield et al. (2010) found recordings of voices to have a
significant effect on participants’ ratings of national park scenes. Additionally, the
increased volume of voice sounds negatively affected emotional ratings such as
annoyance, tranquility, freedom, naturalness, and so on. A number of studies have
focused on the influence of motorized sounds in relation to soundscape experience(Mace,
Bell, & Loomis, 2004; Mace, Corser, Zitting, & Denison, 2013; Weinzimmer et al.,
2014), but findings from the current study along with others, highlight the impact of
voices on negative soundscape experiences.
Based on the regression model results, noise sensitivity was a significant predictor
of soundscape pleasantness. Noise sensitivity relates to sound annoyance and habituation
to noise (reviewed in Benfield et al., 2014). Bivariate correlation results showed a
negative relationship; indicating that those who were more sensitive to noise, found the
soundscape to be less pleasant. These findings are similar to another study that tested the
relationship between noise sensitivity and soundscape perception in a national park.
Benfield et al (2014) found that visitors to Rocky Mountain National Park with higher
54
ratings of noise sensitivity to rate aircraft noise as less acceptable and to rate other man-
made noises as more problematic.
Ability to hear natural sounds and noise sensitivity were factors that related to
individuals’ experience with sound in the park and their personal attenuation to noise.
The variable that measured the average of individuals’ home sound level were objective
measures based on raster data estimating sound levels across the United States. These
findings convey the notion that one’s day to day exposure to sound impacts their
perception of sound during a park experience. Schomer et al. (2013) discussed the role of
community context in soundscape perception. According to their paper, community-wide
context includes elements and norms that are different based on type—urban, suburban,
and rural. For example, common urban sounds like emergency sirens and beeping horns
might be considered normal for a resident living in a large city center, but very unfamiliar
in a rural farm community. Ultimately, when visitors’ leave their home environments to
visit parks, their perception of the park soundscape is impacted by the sound level of their
community.
Q2: How does the sound level of visitors’ home zip code area influence their park
soundscape perception?
Perception of the soundscape is influenced by more than just the physical
measure of sound (Benfield et al., 2014). Thus, it’s important to explore individuals’
characteristics that effect soundscape judgments. Within the environmental noise
literature, it has been concluded that people in different communities perceive identical
sounds to be either less annoying or more annoying based on their personal norms and
attitudes (Schomer et al., 2013). Different from other research outcomes, this study
55
identified a factor beyond attitudes and norms. To the author’s knowledge, this is the first
study of its kind to explore the relationship between the sound level of individuals’ home
zip code and their perception of park soundscapes. However, this is not the first study to
use sound level of zip code blocks to inform a relationship. Andrew et al. (2013) used
aircraft noise contours paired with zip code blocks, to estimate the correlation between
cardiovascular disease in older adults who live near airports.
Our findings suggest the sound level of individuals’ home sound level contributes
to visitors’ perception of the pleasantness of the parks’ soundscape. The multiple
regression model revealed a negative relationship; meaning that as mean sound level of
zip code increased, the rating of soundscape pleasantness decreased. This finding is not
intuitive, one would guess that as sound level of one’s home zip code increases, they
might find the park soundscape to be more pleasant. A previous study found that as
visitation to MUWO increased, so did sound level (Stack et al., 2011). We postulate that
visitors from louder zip codes might have found the soundscape less pleasant because of
increased sound levels due to noise from other visitors.
Results from our spatial analysis also show that a majority of the sample were
from urban areas. In one study, street-level sound level measurements were taken across
New York City to understand sound exposure in an urban community (McAlexander,
Gershon, & Neitzel, 2015). Most locations measured average sound levels above 70 dBA,
which can be detrimental to health and wellbeing. Results from the multiple regression
model demonstrate the impact of individuals’ day to day soundscape experience on
soundscape perception. Parks and protected areas provide individuals’ experiencing
elevated sound levels in their home environment a place of escape.
56
Management Implications
Management of natural soundscapes in protected areas is important for conserving
wildlife, but also providing visitors with holistic benefits. This research demonstrates
how various factors influence the perception of soundscape pleasantness or health.
MUWO designates certain areas of the park as “quiet zones” and empirical evidence
shows that this method is successful in quieting the park (Stack et al., 2011). It’s
important for other parks, especially those close to urban centers, to adopt similar
management techniques. While parks might be quieter than a busy downtown area, it’s
important to keep these protected places quiet, so that visitors have the opportunity
benefit from the ecosystem services they provide.
National Park units across the country are taking steps to implement plans and
policies that protect natural soundscapes. Findings from this study suggest that perhaps
other agencies should begin to develop plans to protect natural sounds and quiet. In a
study of perceived restoration experiences in urban parks, Payne (2008) found that
visitors’ perception of the soundscape plays a significant role in their restorative
experience. Urban parks that can provide experiences that improve the wellbeing of
urbanites should begin to protect natural sound. This can be done by creating zones that
ask visitors to keep quiet, avoid cell phone use, and mute music.
Limitations and future research
Caution should be taken with these results. Sound level of respondents’ zip code
was predicted based on geospatial modeling data supplied by the National Park Service.
This modeling data is likely to contain errors (Mennitt & Fristrup, 2016). For instance,
the model could potentially overestimate or underestimate sound levels in certain areas.
57
Additionally, respondents’ zip code boundary might not represent the sound level they
are exposed to during the majority of the day. It’s likely that individuals live and work in
different zip code boundaries. Thus, their home zip code might not be the most accurate
variable for estimating typical sound exposure.
Our study suggests that individual exposure to sound can impact perceptions of
the park soundscape. However, our study fails to tease out the relationship between noise
sensitivity and the sound level associated with one’s home zip code. Do people choose to
live in rural or quieter areas because they are sensitive to noise? Understanding these
relationships would also help researchers to better understand the connection between
sound level and housing values. Farmer et al. (2013) found that neighborhoods with
higher levels of bird diversity also had higher housing values. Perhaps those who are
sensitive to noise are willing to pay more to live in a quieter area, thus gaining more
opportunities for natural sound exposure. Future research is needed to understand
individual perceptions of soundscapes.
Conclusion
A previous study estimated that 145.5 million Americans experience sound levels
that exceed those recommended to protect public health (Hammer et al., 2014). This
further justifies the importance for protecting parks and spaces where people can
experience the benefits of sounds of nature. Results from this study show that multiple
factors, including the sound level of individuals’ home zip code, influence their
perceptions of soundscapes. This study was successful in determining the relationship
58
between the level of sound one experiences on a daily basis and perceptions of sound.
Professionals can use evidence from this study to inform future research and management
related to natural sounds and the ecosystem services or benefits they provide to human
health and wellbeing
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(2014). The role of messaging on acceptability of military aircraft sounds in Sequoia
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Chapter 3 Aircraft Sound Management in Denali National Park and Preserve
Chapter 3 was written as a stand-alone manuscript that will later be modified for
submission to a peer-reviewed journal. This article seeks to answer:
Q1: How can researchers best inform the development of thresholds for soundscape
quality using dose response methodology?
Q2: What factors influence visitors’ perception of overflight audio clips?
Abstract: Viewing vast landscapes by flight is popular in places like the Grand Canyon, Hawaii
Volcanoes, and Denali National Park and Preserve. Park managers are responsible for planning
and monitoring multiple resources of parks, including the soundscape or acoustical environment
and visitor experience. Therefore, it is important for parks that are viewed by air tours to measure
the impact of aircraft overflight noise on visitor experience. A common method for measuring
visitor response to sound is through a method called dose response. This study used an
innovative, dose response methodology to measure visitor response to aircraft noise in Denali
National Park and Preserve’s frontcountry or more developed area of the park. In previous
studies, audio clips have been used to measure visitors’ reaction to sounds, this study was unique
in that audio clips were played in a random order and potential thresholds were explored using
linear regression. Each respondent listened to 5 randomly chosen audio clips of propeller aircraft
from a suite of 36 clips at varying sound levels. Response to audio clips were predicted using
general mixed linear models. Results show that sound level is an important variable in response to
noise. Additionally, these models help inform thresholds for sound level and the number of
overflights deemed acceptable by visitors.
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Introduction
Denali National Park and Preserve, located in south-central Alaska, is comprised of more
than six million acres of scenic mountains, glaciers, rivers, and forest. Given the vast size of the
park, most visitors only see a small portion of the park during their visit. Like other destinations
in the National Park system, such as the Grand Canyon and Hawaii Volcanoes, viewing the park
by air allows for a bird’s eye view of these expansive landscapes. Unlike high altitude
commercial flights, air tours operate at lower elevations with different types of engines and flight
patterns, thus influencing sound propagation differently. Over 100 national parks are viewed by
air tours and subsequently, visitors on the ground are exposed to aircraft sound (Miller, 2008).
Aircraft overflight noise in parks and protected areas have been shown to impact both wildlife
(Pepper, Nascarella, & Kendall, 2003) and visitors (Benfield et al., 2014; Mace, Bell, & Loomis,
1999; Miller, 1999; Taff et al., 2014). As commercial flightseeing tours gain popularity, park
managers need to understand the impacts of the anthropogenic sounds produced by overflights on
visitor experience.
Noise, defined as an unwanted sound, produced by aircraft overflights have long been
studied in residential areas impacted by airport traffic (Reviewed in Rapoza, Sudderth, & Lewis,
2015). In the community noise context, residents are exposed to air traffic on a more consistent
basis, when compared to park visitors who experience isolated events. Residential studies have
found air traffic noise to impede human cognition, induce stress, and impact other measures of
health (Babisch, 2003; Cohen et al., 1980). Studies that focus on aircraft noise in the park context
aim to better understand the impact of noise on park experiences. Mace et al. (1999) conducted a
laboratory simulation of a park experience and found that aircraft noise at both high and low
levels impacted respondents’ ratings of scenic beauty, naturalness, and solitude. As noise levels
increased, so did annoyance. In a follow up to this study Mace, Bell, Loomis, and Haas (2003),
used similar methods to test the influence of natural sounds paired with aircraft noise on factors
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related to park experiences. They found similar results to Mace et al. (1999), in that increasing
noise negatively impacts park experiences. Benfield et al. (2010) expanded this research even
further and tested the influence of other anthropogenic park sounds on human response. Ground
traffic, voices, and aircraft were compared in terms of their impact on park visitor experience.
Results from this study found aircraft noise to have a negative influence on ratings of scenic
beauty. In other words, noise from aircraft decreased measures of scenic beauty.
Increased noise levels are a growing concern for national parks because as visitation
increases, so does unwanted sounds from transportation (National Park Service, 2006). A recent
study found that anthropogenic noise nearly doubles background sound levels in the majority
(63%) of protected areas in the contiguous United States (Buxton et al., 2017). Several methods
for measuring the impact of noise on park visitor experience have been used (Benfield, Nurse, et
al., 2014; Pilcher, Newman, & Manning, 2009; Stack et al., 2011; Taff et al., 2014; Weinzimmer
et al., 2014). As mentioned earlier, researchers have utilized university laboratory space to
simulate national park experiences. Other studies have used a dose response methodology to
simultaneously measure park sound and visitor response to specific sounds (Anderson, Rapoza,
Fleming, & Miller, 2011; Fidell et al., 1996; Miller, 1999). Commonly the goals of these studies
are to determine a threshold, or point at which aircraft sounds are no longer deemed acceptable.
The purpose of this paper is twofold. First, to build on and improve methods for measuring visitor
response to noise that inform thresholds for soundscape quality. The second purpose is to
understand the factors that influence visitor response to aircraft sound.
Literature Review
Protecting Natural Sound in Parks
People who visit national park sites have a number of different important reasons or
motivations for their visit. Escaping noise ranks as one of the top most important reasons visitors
use parks and protected areas (Driver, Nash, and Haas 1987). In one study that surveyed visitors
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at 39 national park sites across the country, 91% of visitors rated “enjoying natural quiet” as an
important reason for their visit (McDonald et al, 1994). In the same study, 93% of visitors also
rated “viewing natural scenery” as an important reason for their visit, meaning that hearing nature
is just as important as viewing it. Results from these and other studies further justify the
significance of protecting natural sounds for future generations, the main mission of the park
service.
Over the past few decades, the growing concern related to park noise has centered on
aircraft overflights. Grand Canyon National Park gained the most attention due to the growing
popularity of helicopter sight-seeing tours (Reviewed in Mace et al., 2013). Horonjeff et al.
(1993) measured the impact of aircraft noise at the Grand Canyon and found that noise from loud
helicopters to be audible during the majority of the day. In 1987 Congress passed the National
Parks Overflight Act, which required park units to analyze overflight impacts and restore natural
quiet (NPS, 1987). After the 1987 mandate, Congress went on to further direct protection of
natural sounds with Air Tour Management Plans (ATMPs) (NPS, 2000). The purpose of ATMPs
is to prevent noise from commercial air tour operations from negatively impacting park resources
or visitor experiences.
Several studies have demonstrated the adverse effects of hearing aircraft noise in parks.
For example, Tarrant, Hass, and Manfredo (1995) evaluated the effects of overflights on visitors
to wilderness areas in Wyoming. Respondents that were exposed to noise from aircraft reported
lower levels of solitude and tranquility, important characteristics of the wilderness experience.
Other studies have found that aircraft noise can depreciate memory (Benfield et al., 2010),
cognitive function ( Abbott, Newman, Taff Benfield, & Mowen 2015), and landscape
assessments (Weinzimmer et al., 2014). When the effects of aircraft noise are measured at the
community level, it has been found to adversely affect cognitive ability and stress (Haines et al.,
2001).
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Methods used to assess the soundscape vary, but generally audio recording devices are
deployed and sound sources, levels, and frequencies are measured. A common method for
measuring impacts of overflights on visitor experience is through dose response (Anderson et al.,
2011; W. A. Freimund, Vaske, Donnelly, & Miller, 2002; Nicholas P. Miller, 2008; Rapoza et al.,
2015). These studies have included both in-situ dose measures where the park soundscape is
measured in congruence with visitor response to sounds (Anderson et al., 2011), as well as,
simulated where aircraft sounds are played through audio clips (Rapoza et al., 2015).
Dose Response Methods
The dose response method measures the level of sound a participant is exposed to while
simultaneously asking the participant to evaluate their response to varying sound attributes (Fidell
et al, 1996). This methodology has been commonly used to measure human response to sounds in
community noise assessments. For example, Pedersen and Waye (2004) examined residents’
response to wind turbine noise. The NPS also uses this methodology to understand park visitors’
response to both natural and anthropogenic sounds (Anderson et al., 2011; Miller, 1999; Rapoza
et al., 2015). Rapoza et al. (2015) measured noise exposure and visitor response to aircraft noise
in several backcountry national park sites. In other studies, the dose response variable was
estimated by visitors through survey questions. Tarrant, Hass, and Manfredo (1995) asked survey
respondents if they heard aircraft sounds and how often those sounds were audible. Researchers
concluded that respondents had strong negative attitudes towards hearing overflights and were
slightly more affected by hearing overflights than seeing them. Fidell et al. (1996) used both on-
site and telephone surveys to measure the relationship between aircraft noise and annoyance in
wilderness areas. Studies that measure both the physical soundscape and response have been used
to inform reasonable limits for aircraft sound that can aid in park management (Miller, 1999;
Rapoza et al., 2015).
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Studies have utilized both the field and laboratory for analyzing human responses to
sound through dose response methodology. Anderson et al. (2011) calculated dose response
variables for aircraft overflights and matched physical measurements of sound with visitor
surveys at several national parks. In these studies, microphones are deployed in the field and are
used to measure the soundscape visitors are exposed to. From microphone recordings, various
variables related to the physical soundscape can be determined. These can include sound source,
sound level, and percent time sources are audible. Aasvang and Engdahl (2004) utilized field and
laboratory observations to measure outdoor recreationists’ response to aircraft noise near the main
airport in Oslo, Norway. They found that subjects responded similarly to field and lab overflight
noise exposures.
The laboratory setting provides a more controlled measure of dose response than the
field. In most cases, study participants are exposed to audio recordings of soundscapes that aim to
recreate a park experience (Mace et al., 1999, 2013; Weinzimmer et al., 2014). Mace and others
(1999) aimed to simulate a Grand Canyon soundscapes experience where participants were
exposed to high and low levels of helicopter noise. Results from this study found that helicopter
noise interfered with variables related to positive visitor experiences, including the visual
aesthetic quality of landscapes. Weinzimmer et al. (2014), tested human response to a series of
different natural and motorized sounds heard in national parks including: natural sounds,
propeller planes, motorcycles, and snowmobiles. This study also simulated a park experience and
found that all motorized sounds resulted in negative evaluations of landscape quality. While
laboratory settings allow for more control of the specific sound dose and potential confounding
factors, field studies that utilize recorded audio clips sample a realistic group of visitors and don’t
need to suggest a park experience.
Asking survey respondents at a national park to listen and respond to audio clips allows
for more control of the soundscape without having to simulate an already “realistic” park
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experience. Several studies have used this dose response method in the field to understand park
visitors’ response to specific anthropogenic sounds (Marin et al., 2011; E. J. Pilcher et al., 2009;
Taff et al., 2014). For example, Pilcher et al. (2009) used a two-phase study that included in-situ
and audio clip dose response methods to inform soundscape management at Muir Woods
National Monument. Survey respondents were intercepted during their park visit and asked to
listen to sound clips of varying levels of human-caused sound. In another study, Marin et al.
(2011), used dose response methods in the field to understand the role of motivation to hear
natural sound in acceptability of both natural and human-caused sound. This study would have
most likely had a different outcome if it was field based vs. lab based; as park visitors likely have
defined motivations whereas lab participants do not.
Indicators and Thresholds for Soundscape Quality
This study design was developed based on previous research that measured indicators and
thresholds for soundscape quality in national parks (Freimund, Vaske, Donnelly, & Miller, 2002;
Marin et al., 2011; Pilcher et al., 2009). Indicators and thresholds of quality have been used to
guide and develop park management plans and policies (Manning, 2011). They are an integral
part of empirically measuring park carrying capacity for various frameworks including: Limits of
Acceptable Change (Stankey, Cole, Lucas, Petersen, & Frissell, 1984), Visitor Impact
Management (Kuss, Graefe, Alan, & Vaske, 1990), and Visitor Experience and Resource
Protections (National Park Service, 1997; Manning, 2001). An indicator is a measurable variable
based on an identified management goal. These variables can be biophysical, such as
environmental impacts, or social/experiential, such as crowding. Indicators vary depending on
specific management objectives, like whether or not an area is managed for a frontcountry or
wilderness experience. Threshold is defined as the minimum acceptable level of indicator
variables. For example, if crowding and the number of people on a given trail are identified as an
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indicator; the threshold would represent the minimum number of people on the trail that are rated
as acceptable.
Various methods are used to identify indicators and thresholds. Potential indicators can
be determined by interviewing visitors and/or managers, as well as, through surveys with closed
and open-ended questions (Manning, 2011). Normative theory has been a common empirical
approach to informing park thresholds for quality (Manning, 2011; Shelby, Vaske, & Donnelly,
1996; Vaske & Donnelly, 2002). “Norms” can be defined as behaviors that groups or individuals
consider to be “normal” (Manning, 2011). This is usually based on an individual, societal, or
cultural idea. Norms are more powerful than attitudes because they define how people should
behave (Manning, 2011). In this approach, indicator variables are first identified. Thresholds can
be determined or informed by a social normative curve, where acceptability of a park resource or
impact are evaluated. Average ratings of acceptability are plotted with acceptability on the
vertical axis and the resource indicator on the horizontal axis. The point where the level of
acceptability drops below the middle point is considered the minimum level of acceptability. The
value associated with this point is used by park management to inform visitor thresholds for
resource impacts (IVUMC, 2016).
Within the context of soundscapes, Pilcher at al. (2009), conducted a two-phase study to
measure indicators and thresholds to inform soundscape management at Muir Woods National
Monument. In the first phase of the study indicators of soundscape quality were identified
through an in-situ dose response method. Survey respondents rated the sounds they heard during
an attended listening exercise on a scale from pleasing to annoying. Sounds that were heard by a
majority of respondents and rated on average as annoying were determined to be good indicators
of soundscape quality. Noise from groups of visitors talking were identified as a potential
indicator. In phase-two of the study, a threshold for visitor talking noise was determined by using
audio clips. Respondents listened to a series of varying sound levels (dB) of visitor noise and
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rated the acceptability of each clip. On average, respondents rated visitor talking noise above 38
dB as unacceptable. These results aided in informing a threshold for sound quality, and
subsequently, permanent interpretive signage encouraging visitors to be quieter in certain areas of
Muir Woods (Stack et al., 2011).
There are critiques of the normative approach to informing thresholds. First, with more
complex indicators of quality, such as ecological impacts or crowding, visitors might find it
difficult to determine a minimum acceptable number of people of level of impact (Manning,
2011). As a result, visual approaches have been used in a number of studies to measure a range of
crowding scenarios or resource impacts (Heywood, Murdock, Heywood, & Murdock, 2002;
Inglis, Johnson, & Ponte, 1999; Manning & Freimund, 2004). Researchers use pictures of varying
levels of impact to aid respondents in determining acceptable levels. Visual, as well as, auditory
approaches to empirically informing thresholds provide visitors with a more detailed and realistic
way of rating the acceptability of resource conditions; whereas narratives could be awkward and
difficult to understand. Another consideration of these methods is the order in which pictures or
audio clips are presented. For example, in Marin et al. (2011)’s study, audio clips were played for
survey respondents in increasing order, which could have impacted their acceptability rating. The
paper suggests playing clips in a random order so that listeners focus on single recordings and
less on the rating of the previous recording.
More recently, the bias associated with the presentation of photos has been explored,
specifically range and order effect (Gibson, 2011). Most studies present 6-8 photos of increasing
levels of impact and on average, visitor ratings of acceptability drop below zero after the fourth
photo. To understand if the order of photos presented to respondents introduced bias, linear
models were used to test the impact of presentation range and order on acceptability of photos.
Results suggested that the order and sequence of photos did influence respondents’ evaluation.
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Recommendations from these findings suggest using pseudo-random order in presenting survey
respondents with varying levels of resource impact.
Study Purpose
In summary, earlier studies have used dose response methodology to measure national
park visitors’ response to noise in both field and laboratory settings. While lab studies allow for
more control in soundscape experience, laboratory samples are made up of undergraduate
students that don’t accurately represent the motivations and expected experiences of park visitors.
Dose response has also been used to inform the development of indicators and thresholds for
soundscape quality in national parks. However, there are some issues with previously developed
methods. Playing audio clips for respondents in the field allows for a more controlled dose, but
the order in which clips are administered needs to be considered. In Pilcher et al. (2009), audio
clips were played in ascending order. This might have impacted the way in which visitors rated
audio clips. Additionally, Gibson (2011) found that order and sequence of the presentation of
photos biased respondents ratings of acceptability. Therefore, the purpose of this paper is to apply
an innovative methodological approach to informing park thresholds for soundscape quality that
improves the validity of study findings. This study used pre-developed audio clip dose response
methods that allowed for more control and drew from a varied sample of park visitors. We also
utilized a large suite of varying audio clips in a randomized order, which aims to eliminate the
bias potentially associated with clip order, limited sound ranges, and sequence effects.
Methods
Survey Location
Denali National Park and Preserve (DENA) is located in south central Alaska, north of
Anchorage and south of Fairbanks. The park is comprised of six million acres of wildland and a
single access road (NPS, 2017). Travelers come to DENA to view wildlife, hike through alpine
tundra, and either view or climb North America’s tallest peak, Mt. Denali. A substantial amount
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of frontcountry activities take place near the facilities encompassing the Denali Visitor Center
campus. This includes hiking developed frontcountry trails, visiting the Denali Visitor Center,
camping and picnicking, and attending educational programs. These facilities are within close
proximity to anthropogenic sound sources, including an aircraft landing strip, roads, and a train
depot which are sources of potentially unwanted sounds heard by visitors. For this study, visitors
were intercepted at four different survey locations, which allowed for us to sample different types
of frontcountry users (day-use, overnight campers, etc.).
In 2014 DENA completed a report that informed indicators and thresholds of soundscape
quality for backcountry locations (i.e., locations within designated wilderness, managed for
wilderness experiences) (Newman et al., 2014). Data collection for this report spanned several
summers and included in-situ audio clip dose response methods and a listening exercise. The first
phase of this report utilized a listening exercise where respondents reported the sounds they heard
during the three-minute exercise and rated their response to each sound. These data determined
that aircraft overflight noise was an indicator of quality for all backcountry locations. In a second
phase of the study, audio clips were used to inform thresholds for aircraft overflights from three
sources: propeller aircraft, jets, and helicopters. Results from the 2014 report were used in
developing methods for the current study. First, dose response survey methods were replicated for
future comparison between backcountry and frontcountry users. Second, results from the report
helped to identify potential indicators of quality for frontcountry users (e.g. respondents that are
intercepted while using the more developed, frontcountry area of DENA). One of the survey
administration sites in the report, the Triple Lakes Trail, was located near the Denali Visitor
Center Campus. Results from an in-situ listening survey conducted at this location found noise
from aircraft to be an indicator of quality (Newman et al., 2014).
Results from this current study are part of a larger, comprehensive technical report that
measured the current state of soundscapes and their impact on visitors to DENA’s frontcountry.
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Park managers are seeking empirical evidence to inform research questions about the impact of
aircraft overflight noise on visitor experiences in the frontcountry. DENA management is
concerned with the number of commercial flightseeing tours within park boundaries, as well as,
aircraft using the landing strip and the impact of the noise associated with air traffic. Commercial
flightseeing tours most commonly use propeller aircraft. Therefore, park managers are interested
in visitor thresholds associated with propeller aircraft. Results from this study and the technical
report will inform indicators and thresholds for DENA to monitor based on management
objectives.
Audio Clip Dose Response Survey
The survey was administered from June 23rd to July 29th, 2017 at four different locations
within Denali’s frontcountry. These locations included: the Denali Visitor Center (DVC),
Horseshoe Lake Trail (HS), Healy Overlook Trail (HO) trails, and the Murie Science and
Learning Center (MSLC). Surveys were collected at the MSLC on days when inclement weather
made sampling at the HO Trail difficult. During the sampling period, trained surveyors used a
random number generator to choose a number between 0 and 30 that represented the time at
which they would intercept their first visitor group that was either entering or exiting the
sampling location. Because of the high volume of visitors at the Denali Visitor Center,
researchers would intercept every 3rd group they encountered. Due to the medium and low
volume of visitors at the Horseshoe Lakes and Healy overlook trails, researchers would intercept
the 1st visitor they encountered after the last survey was complete. Visitors were then asked if
they would participate in a survey. Visitors who were unwilling or unable to participate in the
survey were asked two questions that assessed non-response bias. Visitor groups who agreed to
participate in the survey were then asked who had a birthday closest to the current date. This
method allowed for randomization within groups. The research assistant then handed the visitor a
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laminated (re-usable) copy of the questionnaire and instructed the respondent to provide verbal
responses that were recorded by the surveyor using a tablet computer.
After answering several demographic questions, survey respondents were asked to listen
to a series of five randomly chosen, 30 second sound clips of propeller aircraft. Respondents were
provided noise canceling headphones (BOSE Quietcomfort 15 Headphones) and asked to listen to
all five recordings until completion. After each audio clip was played, respondents rated the clip
on a 9-point acceptability scale and a 9-point interpretation scale (Marin et al., 2011; Taff et al.,
2014). Audio clips were played through the iPad tablet computer and amplified through the JDS
Labs C5D Headphone AMP+DAC. After the five audio clips were played and rated, the survey
administrator then replayed the clip that was rated as the most acceptable or most pleasing (if
more than one sound clip had the highest rating for acceptability or interpretation, the first sound
clip played was chosen). After listening to the final audio clip (sound clip 6) the respondents then
rated the clip for acceptability of times heard per hour and per day.
Audio clip Development
A pool of 36 different audio clips were developed in order to best represent realistic
propeller aircraft overflight events that occur in DENA’s frontcountry. Each audio clip was
overlaid on a single clip of natural sounds such as wind and birdsong. Each clip was 30 seconds
in length, with the overflight lasting approximately 25 seconds, with the natural sounds playing
for the first few seconds and the last few seconds, thus simulating an actual overflight. The 30
second length of audio clips was chosen based on previous research (Rapoza et al., 2015).
Additionally, this study took place in the field, so longer audio clips could have caused
respondent annoyance or survey fatigue. Overflight audio clips were recorded at several sites
located in DENA’s frontcountry, therefore audio clips were representative of actual overflights.
The research team and DENA staff developed a methodology to best randomize the five
different audio clips that respondents rated during the dose response survey. Script written in
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Python was used to generate over 500 options for random audio clip order, with specific
parameters and guidelines. The first audio clip was chosen randomly from the pool of 36 different
audio clips with varying sound pressure levels. Sound pressure level was expressed in decibels
weighted to reflect human hearing (dB(A)). The audio clip played second had to have a least a
six dB(A) difference from the first audio clip. This difference could have been a higher or lower
sound level. The next three audio clips where chosen randomly with the same parameters. Audio
clips average sound levels were between 50.6 and 78.3 dB(A). There were some limitations to
this method and the sequence of audio clips was not perfectly random. Figure 3-1 shows this
discrepancy. A trend emerged where the second and fourth audio clips played were at a lower
sound level. Survey respondents listened to audio clips that were loaded onto an iPad tablet
computer and played through a portable USB amplifier (JDS Labs C5D Headphone amp+DAC)
and noise canceling headphones (BOSE Quietcomfort 15).
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Response measures
Response measures for audio clips were developed based on those previously used in other dose
response studies (Marin et al., 2011; Stack et al., 2011; A. Rapoza et al., 2015). After each audio clip was
played, respondents rated the acceptability and annoyance of the clips on a 9-point Likert scale (i.e. -
4=very unacceptable to +4=very acceptable, and -1=very annoying to +4=very pleasing). The sixth sound
clip was selected from the previous set by determining which overflight the respondent rated as the most
acceptable or the least annoying. After listening to this sound clip for the second time, respondents were
asked to rate the recording in terms of the acceptability of hearing that sound in minutes per hour. This is
a temporal measurement with varying rates, from once every three minutes to once every hour. Finally,
the instrument asked respondents to rate their acceptability of hearing the 6th audio clip at varying levels
of times per day, as well as, their maximum acceptability for hearing overflights in a given day.
Figure 3-1. Summary of survey response for acceptability for varying
sound levels
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Data Analysis
These data were analyzed using a generalized linear mixed model (GLMM) using the
nlme package for R (R Core Development Team 2014). The purpose of this analysis was to
determine what factors, including sound level (dB), might impact visitor response to aircraft
noise. Eight candidate models were hypothesized based on factors that might influence
respondents’ ratings of the audio clips. These fixed effects or factors included: sound level
(LAeq30s); clip sequence; an interaction with sound level and clip sequence; difference in sound
level from the previous clip (LAeq30s); survey site; and roughness. Sound level was measured as
LAeq, which can be defined as the total A-weighted sound energy level measured over a period
of time. A-weighting weighs the sound pressure level based on human hearing (Austin Noise,
2009). The audio clips were 30 seconds long, so the sound energy level is measured based on an
average of those 30 seconds. Sound roughness can be defined as the “buzzing, rattling auditory
sensation accompanying narrow harmonic intervals” (Vassilakis & Kendall, 2010, p.1). The
roughness measure used in this study was based on the median calculation, expressed as Aspers.
Clip sequence refers to the order in which the clips were played for individual respondents.
For all models the individual respondent was chosen as the random effect. This allows
the model to account for individual biases among the respondents. Best models were chosen
using the AICcmodavg package to extract AIC scores and model weights for candidate models
for each of the factors (Shannon, Crooks, Wittemyer, Fristrup, & Angeloni, 2016). AIC model
weights can be interpreted as the probability that the model is the most predictive given the set of
candidate models. When it is unclear which model is the best, model averaging can be used
choose the best model based on the combined influence of specific parameters and effect size
(Burham & Anderson, 2002). Effect sizes were analyzed by whether the 95% confidence interval
(CI) for each factor overlapped zero. If the CI did not overlap zero, the factor was used in the
final model. Four separate models were analyzed as part of this study. These included annoyance
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of audio clips, acceptability, acceptability of overflights in minutes per hour, and acceptability of
overflights per day.
Results
Audio clip listening surveys were collected from June 24th to July 28th, 2017. The survey
yielded an 85% response rate and 489 completed surveys. At the DVC 160 surveys were
completed, 185 at the HL trail, 115 at the HO trail and 24 at the MSLC. For the purpose of this
analysis, the data was aggregated and not analyzed by site. Final models were chosen based on
results from model averaging. Table 3-1 shows final models, along with AIC corrected weights.
AIC weights are all less than zero, meaning that there was a very low probability of these models
being the “best” models. To eliminate the uncertainty related to choosing best models based on
AIC weights, individual factors that had the most overall strength given the candidate models
were analyzed by their effect size. Final models were determined based on the results in Table 3-
2; where factors whose CI did not overlap zero where used in final models.
Table 3-1. Final GLMM models
Model equations AICc weight
acceptability ~ LAeq30s + clip sequence + site + (subject) <0.0
annoyance ~ LAeq30s + clip sequence (subject) <0.0
acceptability (min/hour) ~ LAeq30s + min length + site + (subject) <0.0
acceptability (times/day) ~ LAeq30s + day length + site + (subject) <0.0
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Table 3-2. Observed relationship between each response variable and the model-averaged
parameters from the final models
Response variable Parameter 𝜷 Estimate (95% CI)
Acceptability LAeq30 seconds -0.11 (-0.12/-0.11)
LAeq30second*Clip Sequence 0.0 (-0.01/0.0)
Clip Sequence -0.12 (-0.16/-0.09)
Difference from previous clip 0.01 (0.0/0.02)
Location 0.67 (0.02/1.131)
Median Roughness -0.02 (-0.02/-0.01)
Interpretation LAeq30 seconds -0.09 (-0.09/-0.08)
LAeq30second*Clip Sequence 0.0 (-0.1/0.0)
Clip Sequence -0.09 (-0.12/-0.6)
Difference from previous clip 0.0 (-0.01/0.01)
Location 0.44 (-0.11/0.99)
Median Roughness -0.01 (-0.02/-0.01)
Acceptability (minutes per hour) LAeq30s (Clip 6) -0.03 (-0.05/0.0)
Length (min per hour) -0.13 (-0.14/-0.13)
Location 0.24 (0.05/0.43)
Acceptability (times per day) LAeq30s (Clip 6) -0.01 (-0.03/0.01)
Length (times per day) -0.05 (-0.05/-0.05)
Location 0.19 (0.01/0.36)
*Bold text denotes 𝛽 estimate with 95% CI that do not overlap zero.
Acceptability
The results for all sites combined, using model averaging (Table 4) showed that LAeq,
clip sequence, and location were key explanatory variables. The predicted outcome based on the
final model (Figure 3-2) showed that low levels of noise were rated as acceptable, but as noise
level increases, acceptability decreases. Acceptability varied by site and was determined to be a
contributing factor to the overall model. All three hypothesized variables for acceptability of
aircraft express in minutes per hour were key contributors to the model: LAeq, length (minutes
per hour), and location. The predictive regression model (Figure 3-3) found that hearing aircraft 3
minutes per hour was rated as slightly acceptable at all sound levels. Hearing aircraft for nine
minutes or more per hour was rated as unacceptable at all noise levels. For the acceptability of
times per day, both length (in times per day) and location were key contributors to the final
model. While LAeq did not overlap the 95% CI, it was left in the final model because LAeq is an
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important component of the model outcome. The predictive regression model (Figure 3-4)
showed that hearing aircraft one time per day was acceptable at all noise levels. At 10 times per
day all noise levels were rated as slightly unacceptable or almost neutral. Twenty-five times per
day was rated as unacceptable and 50 to 100 times per day was rated very to extremely
unacceptable at all noise levels.
Figure 3-2. Predicted relationship between visitor acceptability and aircraft noise level using
survey data collected at all sites (MSLC, HL, HO, and MSLC).
Figure 3-3. Predicted acceptability models by number of overflights (3, 9, 15, or 30 minutes per
hour). Solid lines represent the predicted relationship between acceptability and sound level
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Figure 3-4. Predicted acceptability models by number of overflights (1, 10, 25, 50, or 100 times per
day). Solid lines represent the predicted relationship between acceptability and noise level.
Interpretation
For the interpretation response, LAeq and clip sequence were found to be the two key
factors in the hypothesized models. Based on the results from the predicted model, low noise
levels were rated as slightly annoying or neutral, but as noise level increased, annoyance
increased (Figure3-5). Surveys were deployed at four different locations in DENA’s frontcountry.
Location of the survey was not a key factor in predicting annoyance.
Figure 3-5. Predicted relationship between visitor interpretation (pleasing to annoying) and
aircraft noise level using survey data collected at all sites (MSLC, HL, HO, and MSLC).
.
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Numerical Threshold
Respondents were asked follow up questions regarding their response to the 6th audio clip
(the clip rate as the most acceptable/pleasing). Seventy-six percent of respondents indicated that it
would be OK to hear some small aircraft sound as they heard in sound clip six (Table 3-3). Of
those who indicated it would be OK to hear some aircraft sounds, 18% indicated they would
prefer to hear no more than one flight per hour, 27% indicated they would prefer to hear no more
than 2 flights per hour, and 27% indicated they would prefer to hear no more than 3 small aircraft
sounds per hour.
Table 3-3. Acceptability of hearing small aircraft sounds from recording #6 (flights per hour)
Percent of
respondents
Preference of flights per hour
Mean1 Minimum Maximum SD
OK to hear some 76 8.8 1 2000 103.8
Prefer to never hear 24 - - - - 1Median = 3.
Over half of the sample (55%) specified a number of overflights they could hear before they
would no longer visit DENA (Table 3-4). Of the 55% who specified a number of overflights, the
median number was 25 overflights flights per day. Forty-five percent of respondents indicated
that they would visit DENA frontcountry regardless of the number of overflights heard.
Table 3-4. Acceptability of hearing aircraft sounds from recording #6 (times per day) before
respondent would no longer visit Denali
Percent of
respondents
Flights per day
Mean1 Minimum Maximum SD
No more than… 55 45.5 1 1000 74.7
I would visit regardless of
how many aircraft heard 45 - - - -
1Median = 25.
The majority of respondents reported hearing aircraft during their time in DENA (66%).
Table 3-5 shows results from the question, “if you heard aircraft, how bothered, disturbed, or
annoyed were you by other aircraft?” Forty-five percent of the sample reported being not at all
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bothered, disturbed, or annoyed. However, over half (51%) reported being slightly-moderately
bothered, disturbed, or annoyed by other aircraft.
Table 3-5. Respondents bothered, disturbed, or annoyed by other aircraft
Bothered, disturbed, or
annoyed by other
aircraft
Percentage
Mean1 SD Not at all Slightly Moderately Very Extremely
DVC 43 36 18 3 1 1.8 0.9
HL 43 34 18 7 3 1.8 1.0
HO 52 27 14 5 1 1.8 1.0
MSLC 33 27 40 0 0 2.1 0.9
Overall 45 33 18 2 2 1.8 0.9 1Annoyance based on 5-point scale (1 = Not at all; 2 = Slightly; 3 = Moderately; 4 = Very; 5 =
Extremely)
Discussion
The purpose of this study was to explore an innovative method for informing thresholds
for soundscape quality. A dose response method that drew from a pool of 36 varying levels of
propeller aircraft sound was utilized. This chapter will discuss the research findings, managerial
implications, and directions for future research.
Q1: How can researchers best inform the development of thresholds for soundscape quality
using dose response methodology?
Aircraft noise in national parks can be an indicator of soundscape quality therefore
negatively impacting visitor experience. Results from Newman et al. (2014) found aircraft to be
an indicator of soundscape quality near DENA’s frontcountry. Response to the propeller aircraft
sounds heard by respondents were rated on average as ‘annoying’, suggesting its impact on
quality visitor experience. Additionally, results from the current study showed that of the
participants that reported hearing aircraft sounds during their visit to DENA,over half (51%)
reported being slightly-moderately bothered, disturbed, or annoyed by other aircraft. Our study
built on previous dose response methods to inform potential thresholds for propeller aircraft
93
sounds (Pilcher et al., 2009; Rapoza et al., 2015). To better control for propeller aircraft exposure,
respondents listened to five audio clips of varying levels of propeller aircraft, chosen randomly
from a suite of 36 clips.
This study was different from others that have utilized audio clips because of the large
suite of varying levels of propeller aircraft sounds that were played in a random order for each
respondent. This randomization technique helped improve the validity of responses to sound.
Pilcher et al, (2009) used five different levels of audio clips in Muir Woods to determine a
soundscape threshold. Audio clips were played in an ascending order, which has been shown
impacted how study participants responded (Gibson et al., 2011). Our study was also unique in
that a wide range of varying audio clips were used. In other studies that use dose response, a
fairly small suite of audio clips are used for comparison (Mace et al., 1999; E. J. Pilcher et al.,
2009). Only 5 audio clips that ranged from 31 to 48 dB were used in Pilcher et al. (2009).
The techniques used to analyze responses to audio clips were also more robust. Pilcher et
al., (2009) used mean ratings of audio clips to determine the point at which the majority of the
sample no longer deemed the sound clips acceptable (i.e. the point at which the average ratings
fall out of the acceptable range and into the unacceptable range). In the current study, general
linear mixed models (GLMM) were used to predict visitor response to varying levels of audio
clips. GLMM regression models are powerful in that they account for the variation or random
effects of independent variables (Burnham & Anderson, 2002). Results from model averaging
showed that random effects of each individual were an important contribution to final models.
Additionally, multi-variate regression analysis allows researchers to better understand which
variables may or may not contribute to respondents’ evaluation of audio clips.
Ultimately, the large suite of varying sound levels in audio clips and robust analysis used
in this study provide a more rigorous and accurate understanding of potential visitor thresholds.
Park managers and researchers that are interested in determining thresholds for soundscape
94
quality should consider adapting this methodology in order to answer complicated research
questions. Sounds are a complex resource that require a more vigorous approach to measuring
and understanding how visitors respond to them.
Q2: What factors influence visitors’ perception of overflight audio clips?
Results from generalized mixed linear models showed that visitors’ response to sound
depends largely on the loudness of specific noise sources. Sound level (LAeq30s) was an
important factor in all four regression models. This finding was consistent with Pilcher et al.
(2009) who determined that the level of visitor noise impacted visitor dose response in Muir
Woods National Monument. Results from predicted regression models also show that visitors are
annoyed with propeller aircraft noise, even at low sound levels. These findings are in line with
other studies that have found park visitors to report annoyance with aircraft at both low and high
levels (Mace et al., 1999; Benfield et al., 2010; Rapoza et al., 2015; Fidell et al., 1979).
Clip sequence, or the order in which audio clips were played was an important factor in
predictive models for both acceptability and annoyance. This finding further justifies the
importance of playing a random order of varying levels of audio clips. As Pilcher et al. (2009)
suggested, the order in which audio clips are played my impact visitor response, especially if
clips are played in an ascending or descending order. These results also build upon Gibson’s
(2011) study that suggested when survey respondents are exposed to sound clips or pictures of
varying levels of impact, responses regress to the mean. Testing a wide range of sound levels that
are randomly assigned to visitors improves the validity of regression results.
For the models that predicted acceptability, and acceptability by hour and day; location or
site of the survey was an important factor. An interpretation of this finding could be that
acceptability of specific sounds change by location. For instance, propeller aircraft sounds might
95
be perceived as less acceptable while hiking when compared to hearing them outside the Muirie
Science and Learning Center. As reviewed in Zinn et al. (1998), normative beliefs related to
recreational management are influenced by situation specifics. Zinn et al.’s (1998) study found
that acceptability of mountain lion management was dependent on situational context. In this
study, the specific location of the intercept survey was important. Additionally, this finding
signifies the influence of testing visitor reaction to sounds in-situ, rather than in a laboratory
experience. Lab participants don’t have the same motivations and experiences as park visitors.
Because of this, findings from this study can be generalized to the population of visitors to
DENA.
Management implications
Results from the audio clip survey aimed to inform thresholds for aircraft noise that
management can use to better understand acceptable sounds levels for aircraft and the point at
which the number of aircraft are deemed unacceptable. Propeller aircraft sound level is predicted
to be rated as unacceptable by visitors at about 54 LAeq. These results also suggest a numerical
threshold for hearing aircraft. Hearing aircraft at three minutes per hour was slightly acceptable
for lower sound levels (<60 LAeq), and became unacceptable at higher levels (>60 LAeq).
Hearing aircraft at any sound level for 9 or more minutes per hour was rated as slightly to very
unacceptable. Hearing aircraft once per day was rated as acceptable for most sound levels, but
hearing aircraft for 10 or more times per day was rated as slightly to very unacceptable at all
sound levels. Finally, respondents were asked, after listening to the 6th sound clip, how many
overflights they could hear, as they heard in sound clip #6, before they would no longer visit the
park. Fifty-five percent of the sample indicated a specific number of flights they could hear
before they would no longer visit the park. On average this number was 45.5 flights per day.
96
The next step for DENA management would be to determine if the number of flights are
currently violating thresholds. For example, how many overflights per day are heard in DENA’s
frontcountry and what are the sound levels associated with those flights. Determining a threshold
for overflights will also depend on management objectives for managing the frontcountry areas of
DENA. For example, if a management objective is to provide visitors with the ability to
experience natural quiet and sounds of nature, which is mandated by the NPS, overflight noise
might create a masking effect. Additionally, if thresholds are being violated, it is important for
management to review the amount of commercial air tours deemed acceptable, and determine the
appropriate number of take offs and landings for the airstrip located within the park. It is
important for management to monitor the sound level of takeoff and landing events that occur
within the park. It’s possible that the sound level and number of events violate thresholds and
contribute to negative soundscape experiences.
Conclusion
This study broadens the application of indicators of quality and thresholds that are used in
managing parks and protected areas. This method for informing thresholds for soundscape quality
builds on other dose response studies and is improved by the use of an extended library of
varying audio-levels. This study used general linear mixed models, as opposed to using averages,
to predict visitor response to a wide range of varying sound levels. This method proved to be
more robust and increase measurement validity. Sound level and audio clip sequence were shown
to be important variables for modeling response to sound. These findings are valuable to future
studies and signify the importance of presenting survey respondents with a random order of audio
clips.
While the results from this study are specific to frontcountry use in DENA, methods can
be adapted to other national parks. It can be applied to other parks and protected areas that are
subject to impacts from commercial aircraft tours. Moreover, the method of developing varying
97
levels of audio clips can be used for other anthropogenic soundscape indicators such as: vehicles
including personal, bus, and motorcycle, as well as voices, generators, and other aircraft types.
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Chapter 4 Visitor Preferences for Soundscape Management in Muir Woods National
Monument
Chapter 4 was written as a stand-alone manuscript that will later be modified for
submission to a peer-reviewed journal. This article seeks to answer:
RQ1: What tradeoffs are visitors willing to make in order to hear natural sounds
in Muir Woods National Monument?
RQ2: Are the trade-offs made by visitors different in the treatment group (signs
present asking visitors to maintain quiet) vs. the control group (all signs are
covered)?
Abstract: National Park managers are mandated to protect natural sounds for both
wildlife and visitor experience. Enjoying natural quiet and sounds of nature is an
important motivation for visitors to National Parks. Researchers have used both policy
and studies of visitor motivations to justify the significance of protecting natural sounds.
The purpose of this study was to explore the tradeoffs visitors make in order to achieve a
more natural soundscape. Do visitors support more intensive interventions from
management in order to hear more natural sounds? This study also tested the differences
in preferences between respondents who were exposed to educational signs that asked
visitors to be quiet and respondents who didn’t view any signs. Results indicated that
respondents preferred indirect forms of management, such as educational signs and
rangers asking visitors to maintain quiet in the park. Additionally, respondents who were
exposed to signs, had a significantly higher preference for indirect management
interference than the control group who was not exposed to signs.
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Introduction
In 2016 the National Park Service (NPS) celebrated their 100th anniversary. The
celebration and extra promotion of National Parks led to a record breaking year with over
330 million recreation visits (NPS, 2018). In general, visitation to National Parks has
been increasing (Warnick, et al. 2012) and thus making the NPS mission difficult to
achieve. Park managers are tasked with ensuring the balance of protecting natural and
cultural resources, while providing positive experiences for park visitors. Soundscapes,
defined as the acoustic environment (Newman, Manning, & Trevino, 2009, p. 2), are
included in the list of resources managers are tasked with preserving for the enjoyment of
future generations. With record numbers of visitors traveling to national parks, natural
soundscapes are masked by transportation and other noise caused by visitors. In fact,
elevated levels of noise have been estimated to impact a large portion of protected area
units (Buxton et al., 2017).
Visitors choose to recreate in National Parks for a number of different reasons,
but the motivation to enjoy quiet and natural sounds is common among visitors (Haas &
Wakefield, 1998; Marin et al., 2011). Natural soundscapes have also been shown to
provide humans with benefits. For example, natural sounds such a birdsong, have been
found to improve mood (Benfield, Taff, et al., 2014), cognitive restoration (Abbott et al.,
2015), and landscape assessment (Weinzimmer et al., 2014). Conversely, anthropogenic
or man-made sounds can negatively impact physiological measures, such as stress and
heart rate (Hammer et al., 2014). Sounds from sources such as aircraft and transportation
have been found to impede on positive park experiences (Mace et al., 2013; Tarrant,
Haas, & Manfredo, 1995). Sounds from visitors talking have also been identified as a
109
factor that impacts the natural soundscape and positive experiences (E. J. Pilcher et al.,
2009).
Motivations have been used as a powerful tool in understanding the important
reasons visitors travel to national parks, which includes the opportunity to hear natural
sounds. However, these data tell us little about the value park visitors place on
soundscapes and protecting them. Past research has shown that park visitors are willing to
make tradeoffs in order to achieve desired experiences (Bullock & Lawson, 2008;
Newman, Manning, Dennis, & Mckonly, 2005; Newton et al., In press; Pettebone et al.,
2011). Stated choice modeling has been used to measure visitors’ preferences and
tradeoffs for social, natural, and managerial experiences in parks.
Park managers use multiple strategies to improve the quality of park resources,
this includes different levels of management interference. Management strategies can be
more “heavy handed” and infringe on visitor freedoms. While other strategies are
considered “light handed”, where education can be used to achieve management
objectives. The purpose of this paper is to explore the tradeoffs visitors make to achieve a
high-quality soundscape experience and the levels of management that are most
preferred.
Literature
Soundscape Management
Similar to other natural resources like wildlife and water, NPS managers aim to
protect natural sounds. The NPS Soundscape Management Policy 4.9 requires National
Park units to measure acceptable sound levels and mitigate noise (NPS, 2006).
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Soundscape management is important for maintaining both wildlife habitat (Francis &
Barber, 2013) and quality visitor experiences. Visitor Experience and Resource
Protection (VERP) is the specific framework used by the NPS for managing carrying
capacity and other issues related to increased visitor use (Manning, 2001). This
framework has been used to measure and mitigate anthropogenic sounds that threaten the
sustainability of quality park experiences.
Pilcher, Newman, & Manning (2009), used the VERP framework to identify
indicators and thresholds for soundscape quality in Muir Woods National Monument.
Noise from other visitors (talking, screaming, etc.) was identified as a potential indicator
of quality. This study also determined a threshold for soundscape quality based on sound
levels produced by visitors in the park. Ultimately, these thresholds were being violated
by increased sound levels caused by visitors. A follow up study aimed to reduce noise
caused by visitors through testing the efficiency and acceptability of signs that asked
visitors to be quiet (Stack et al., 2011). This study used an experimental design to test
differences in park sound levels and visitor response to the signs. The educational signs
were found to be effective in lowering sound levels in the park. Visitor noise decreased
by 3 dB(A), which then doubled the opportunity for visitors to hear natural sounds.
Additionally, visitors were highly supportive of the signs as a management practice.
Management Strategies
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In order to achieve the balance of resource protection and quality visitor experience,
researchers and managers have been tasked with understanding the effectiveness of
different strategies for managing human behavior (Bullock & Lawson, 2008; Park,
Manning, Marion, Lawson, & Jacobi, 2008) . This topic is reviewed in Manning (2011),
essentially there is a spectrum of strategies that span between “heavy handed” or direct
approaches and “light handed” or indirect approaches. Direct management strategies
apply regulatory measures to change visitor behavior, while indirect strategies aim to
impact visitors’ decision-making process to influence behavior (Manning, 2011). An
example of a direct management strategy would be closing a specific trail to reduce
crowding or restore a trail from human impact (Hockett, Marion, & Leung, 2017).
Informational or educational signs are a form of indirect management that can alter
visitor attitudes or perceptions (Manning, 2003).
In some cases, an experimentally designed study is used to test the effectiveness of
different direct and indirect management treatments. Park et al. (2008) tested visitor
behavior outcomes related to either direct (closed trails) or indirect (educational)
treatments to keep visitors from hiking off trail. Within the context of soundscape
management, Stack et al. (2011) also used an experimental design to test the
effectiveness of educational signs in MUWO that denoted either a “quiet zone” or a
“quiet day”. Results demonstrated that indirect management in the form of educational
signs to be effective in lowering park sound levels. Additionally, visitors found the signs
to be an acceptable management intervention. In another study, Taff et al., (2014), used
educational messaging in Sequoia National Park to improve visitors’ acceptability of
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military aircraft noise. The results of these studies suggest that indirect management is
useful for shifting visitor behavior and perceptions of park soundscapes.
Stated Choice Modeling.
Stated choice modeling was initially used in market research to understand
preferences in product design (Louviere, Hensher, & Swait, 2000). This method is used
to help researchers understand how people evaluate choices and the tradeoffs they make
in order to obtain the best possible condition. Respondents of stated choice surveys are
asked to make a series of distinct choices between two or more scenarios that have
multiple levels of attributes. For example, when buying a new car, one has the option of
choosing from an overwhelming number of accessories (i.e. leather interior, power
windows, satellite radio, etc.). The method of stated choice modeling can tell us about the
types of choices and “trade-offs” a sample of consumers might make. These results aid in
more precise product development and manufacturing.
This method has also been applied to park and recreation management (Bullock &
Lawson, 2008; Newman, Manning, Dennis, & Mckonly, 2005; Newton et al., In press);
Pettebone et al., 2011). Rather than measuring preferences for products, stated choice has
been used to measure visitors’ preferences and tradeoffs for social, natural, and
managerial experiences in parks. Newman et al. (2005) studied the tradeoffs of
backcountry users in Yosemite National Park’s wilderness areas. This study used a
survey with paired comparisons to determine respondents rated signs of human use at
backcountry campsites to be an important indicator of quality. Moreover, this method
allowed for researchers to provide Yosemite National Park management with the results
113
of the model, which indicated that respondents were willing to deal with more stringent
management in order to gain quality in the appearance of campsites.
In another study, Bullock and Lawson (2008), used stated choice to understand
visitor preferences for management at Cadillac Mountain, in Acadia National Park.
Attributes for management conditions included varying levels of management
interference, ranging from freedom and open access to turning many visitors away from
visiting the summit during busy times. The study also included attributes for social
conditions (the number of people on the trail) and resource conditions that reflected
varying levels of visitor caused environmental damage. During data collection,
respondents were presented scenarios that described a narrative of varying attributes, as
well as, a photo that portrays the attribute narrative. Results from this study identified
visitors’ preference towards protecting the environmental resources on the summit.
Additionally, they are in favor of rigorous management implications, but prefer the
summit to be open access. These findings allow for management to understand the
specific preferences of victors to this iconic park summit.
Researchers have also used stated choice modeling to understand park visitor
preferences off the trail. Pettebone et al. (2011) used this method to investigate visitors’
preference for traveling within the Bear Lake Road area of Rocky Mountain National
Park. Due to increased use, the NPS is using alternative transportation, like bus systems,
to move visitors through parks. This study analyzed varying attributes related to
destination convenience, traffic and visitor volume, and number of hikers on a trail.
Photos were also utilized to depict different scenarios. Results from this study found that
visitors prefer to use their personal vehicles in the park. They were willing to tradeoff
114
using their personal vehicle and use the bus transportation to avoid congestion on the
roads and trails. These data were useful to managers who can then use this information to
design a transportation system and encourage visitors to use the bus rather than deal with
vehicle traffic.
Study Justification
Golden Gate National Recreation Area, located north of San Francisco, held first
place for recreation visits in 2016 with over 15 million visits (NPS, 2017). Visitation at
nearby Muir Woods National Monument (MUWO) has also been steadily increasing and
exceeds one million visits per year (NPS, 2017). Due to increased visitation to this
relatively small park, reservations are now required for all personal vehicles and shuttle
riders visiting MUWO. MUWO management values the protection of natural sounds and
has made a concerted effort to improve the natural soundscape using empirical evidence.
The Cathedral Grove section of the park is a designated “quiet zone”. This was a result of
Stack et al.’s (2011) study that informed the success of using educational signage to quiet
visitors.
To date no study has used stated choice modeling to understand if visitors are willing
to make tradeoffs in order to experience a more natural soundscape. The purpose of the
study was to explore tradeoffs at MUWO, a park with growing visitation and potentially
increased noise levels. Similar to Stack et al., (2011), an experimental design was used to
test differences in tradeoffs on days when educational signs were present (treatment) and
days when signs were covered (control). The study answers two questions:
115
Research Questions
RQ1: What tradeoffs are visitors willing to make in order to hear natural sounds in
Muir Woods National Monument?
RQ2: Are the trade-offs made by visitors different in the treatment group (signs
present asking visitors to maintain quiet) vs. the control group (all signs are covered)?
Methods
Study Site
Visitor intercept surveys were collected in the summer of 2016 at Muir Woods
National Monument (MUWO), which is located north of San Francisco, California (See
Figure 4-1). MUWO is a popular destination for tourists and includes 500 acres of
redwood trees, with hiking trails throughout. People are drawn to this park to experience
the towering and awe inspiring old growth coastal redwood forest. MUWO is also a park
that is keen on protecting its natural sounds. Since 2005, the park has supported a number
of different soundscape related studies (Marin et al., 2011; E. Pilcher, 2006; Stack, Peter,
Manning, & Fristrup, 2011). For example, a study conducted by Stack et al. (2011), used
signs asking visitors to keep quiet to test whether or not they were effective and quieting
visitor noise and improving visitors’ experiences. They found a significant decrease in
sound level with the presence of this signage. Results from this research led to the park’s
use of permanent signs that name the cathedral grove area of the park a “quiet zone”.
116
Figure 4-1. Map of San Francisco Area
Experimental Design
Similar to methods used by Stack et al. (2011), educational treatments were used
to designate “quiet days” (treatment) and “control days” during the study period.
Treatment and control mitigations were used in week long blocks. During the treatment
or “quiet” days, educational A-frame signs (e.g., ‘Enter Quietly’, ‘Maintain Natural
Quiet’, ‘What you can do to help natural soundscapes’) along a ~0.6 km segment of the
main trail system (See Figure 4-2). During control days, all educational signs related to
maintaining quiet were removed or covered.
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Figure 4-2. Educational Signs (used in treatment weeks)
Survey Administration
Visitors were intercepted and asked to participate in the survey as they were
exiting the trail corridor. Sampling days were stratified by weekend and weekday, control
and treatment, and time of day. Survey participants were given a laminated copy of the
survey questionnaire. The research assistants read the instructions and used tablet
computers to input the responses. Tablets are used to facilitate skip patterns and minimize
data entry errors.
The survey included measures of visitor motivations, interpretation of the park
soundscape, noise sensitivity and questions to determine tradeoffs for preferred
118
experiences. Tradeoff modeling attributes were chosen for this study based on realistic
management scenarios and varying ranges of acoustical environments (See Figure 4-3).
These attributes included 1) percent time hearing natural sounds, 2) varying degrees of
management actions, and 3) temporal trail closures.
Choice Experiment Design
The experimental design for choice models is an important step in the survey
planning phase. Essentially, it is unreasonable to ask survey respondents to respond to all
possible variations of the choice attributes that are presented in Figure 4-3. Moreover, the
design of choice sets should aim to reduce the amount of mental effort needed to respond,
so as to not impair respondents’ cognitive ability (Ferrini & Scarpa, 2007). The goal of
model design is to develop a condensed collection of discrete choice scenarios that are
manageable for an intercept survey and will best measure respondents’ tradeoffs. An
efficient design was used to determine which attribute combinations will most effectively
measure the sample populations’ tradeoffs among attributes.
We used an efficient design to create choice scenarios that would best measure
visitor preferences. Efficient designs “maximize the information from each choice
situation” and are tested for their level of efficiency using the D-statistic (Rose &
Bliemer, 2009, p.590). This method accounts for random parameters, as well as,
estimated sample size to develop blocks of multiple-choice scenarios. The design was
generated using Ngene (D-error = 0.7836). Initially, 18 choice sets were developed and
then blocked into two survey versions. Each respondent reviewed nine paired
119
comparisons and were asked to choose which scenario they most preferred (See Figure 4-
4). Moreover, respondents did not have the option to choose neither scenario if both were
not preferred.
Variable Levels
Per
cent
Tim
e
hea
ring N
atu
ral
Sounds
1 You can hear natural sounds (e.g. birdsong, small mammals) most of the time
(about 75% of the time)
2 You can hear natural sounds (e.g. birdsong, small mammals) about half of the
time (about 50% of the time)
3 You can hear natural sounds (e.g. birdsong, small mammals) some of the time
(about 25% of the time)
4 You can rarely hear natural sounds (e.g. birdsong, small mammals) (about 5%
of the time)
Man
agem
ent
Act
ions
1 No signs are posted along the trail about natural quiet
2 Signs are posted along the trail educating visitors about natural quiet
3 Signs are posted along the trail educating visitors about natural quiet & asking
visitors to limit noise
4 Signs are posted along the trail educating visitors about natural quiet & asking
visitors to limit noise, and rangers are stationed along the trail to limit visitor
caused noise
5 Signs are posted along the trail educating visitors about natural quiet & asking
visitors to limit noise, and rangers are enforcing visitors to limit their noise
along the trail
Tem
pora
l
Clo
sure
s 1 Trails are open during operating hours
2 Trails are closed for one hour after dawn for the morning breeding bird chorus
3 Trails are closed for one hour after dawn & one hour before evening for the
breeding bird chorus
Figure 4-3. MUWO Stated Choice Attributes
120
Figure 4-4. Example of choice scenario
Model Analysis
The results of respondents’ scenario choices were analyzed using a random
parameter logit model. This model type assumes the marginal utility of each of the
attributes to have normal distribution and unobserved variability among survey
respondents (Reviewed in Shr and Read, 2016). Marginal utility scores represent the level
of importance respondents place on each attribute. In preparation for model analysis, data
from the preferred management scenarios were dummy coded (Louviere et al., 2001).
Essentially, the scenario chosen by each respondent was treated as the dependent variable
and coded as either “1” or “0”. The independent variables represented the varying levels
of acoustic and management indicators. These were also labeled with effect codes so that
the base or reference level of each indicator is omitted in the estimation, while the
coefficients of the base level are calculated by the negative sum of all other coefficients
of other levels.
121
In this study, the first level was used as the reference (e.g. “No signs are posted
along the trail about natural sound” and “Trails are open during operating hours”). That is
to say, base attributes were treated as the “cost” for achieving other attributes. For
example, respondents might prefer to see signs along the trail and ranger enforcement of
quiet to avoid trail closures at dawn and dusk. Utility scores were generated by regressing
the effect coded variables.
One of the main goals of this stated choice analysis was to measure the
differences between the treatment and control group. This was achieved by fixing the
parameters for natural sound. It was assumed that results from the natural sound attribute
would be non-random. In other words, we speculated that respondents in either group
would have the same preference for sound. This strategy allowed for a comparison
between utility scores for the treatment and control groups.
Results
Sample Profile
Visitor-intercept surveys in MUWO were collected between May 9th and May
21th, 2016. A total of 537 (n=537) surveys were collected with a 55% response rate. This
response rate is low for intercept surveys in National Parks, but it is similar to other
studies that have been conducted in Muir Woods (Marin et al., 2011; Stack et al., 2011).
Of the respondents who answered demographic questions, 84% reported living in the
United States and 16% lived outside of the United States. Forty six percent of the sample
reported their gender as male and 54% reported gender as female. The mean age was 45
122
years old, and ranged between 18 and 92 years of age. Sixty four percent of respondents
were first time visitors to MUWO. On average, visitors spent 2.18 hours in the park, and
ranged between 1 and 6 hours. We also asked visitors “How would you describe your
group?” Sixty-five percent of respondents described their group as family. Eighteen
percent reported being with friends, 6.6% were alone, and 7% were with family and
friends. Less than one percent reported their group as a commercial tour group.
Stated Choice Model
In Table 4-1, results of the random parameter logit model are presented. The
mean coefficient associated with each attribute indicates relative importance or the
“marginal utility score” of the attribute. The further the coefficient is from zero, the
higher the relative importance. The direction of the mean coefficient relates to either a
positive or negative preference. Additionally, in this model, the attributes for natural
sound were condensed and treated as a continuous variable because the attribute levels
are considered linear (e.g. “You can hear natural sounds 75% of the time”).
Results from Table 4-1 depicts the model results for both the treatment and
control group. The fixed mean score for the natural sound attribute was positive. Based
on previous literature this finding is intuitive, in that visitors would have a higher
preference for hearing natural sounds a larger percent of the time. Results related to each
group of attributes are discussed in the following sections.
123
Table 4-1. Parameter Estimates for the Latent Class Model
Treatment (Signs Displayed) Control (No Signage)
Choice Attributes Mean
(Std. Err.)
Std. Dev.
(Std. Err.)
Mean
(Std. Err.)
Std. Dev.
(Std. Err.)
Natural Sounds
You can hear natural sounds (e.g.
birdsong, small mammals) X% of the
time (Condensed)
0.176***
(0.02)
0.106***
(0.018)
Fixed across groups
Management strategies
1.No signs are posted along the trail
about natural quiet
-- -- -- --
2. Signs are posted along the trail
educating visitors about natural quiet
1.692***
(0.258)
1.373***
(0.371)
1.257***
(0.278)
1.535***
(0.392)
3. Signs are posted along the trail
educating visitors about natural quiet and
asking visitors to limit noise.
2.606***
(0.230)
0.670*
(0.375)
1.953***
(0.220)
0.691**
(0.341)
4. Signs are posted along the trail
educating visitors about natural quiet and
asking visitors to limit noise, and rangers
are stationed along the trail to limit visitor
caused noise.
2.015***
(0.269)
1.966***
(0.300)
1.723***
(0.294)
2.230***
(0.524)
5. Signs are posted along the trail
educating visitors about natural quiet and
asking visitors to limit noise, and rangers
are enforcing visitors to limit their noise
along the trail.
1.143***
(0.288)
2.163***
(0.341)
0.487
(0.329)
2.618***
(0.455)
Closures
1. Trails are open during operating hours -- -- -- --
2. Trails are closed for one hour after
dawn for the morning breeding bird
chorus
0.163
(0.215)
1.151***
(0.283)
0.115
(0.231)
1.418***
(0.280)
3. Trails are closed for one hour after
dawn & one hour before evening for the
breeding bird chorus
0.092
(0.237)
1.281***
(0.301)
0.303
(0.259)
1.765***
(0.265)
Number of choice questions 4296
Number of parameters 43
Log-likelihood ratio -2113.28
Pseudo R2 0.2873
Note: ***, **, * significant at 1%, 5%, and 10%, respectively; all parameters are assumed to be normally
distributed, while correlations are allows only within the levels of each attribute.
124
Table 4-2. Differences in marginal utility scores between the treatment and control groups
Choice Attributes Difference Asymptotic t-
ratioᵃ
p-value
Management strategies
1.No signs are posted along the trail about natural
quiet
-- -- --
2. Signs are posted along the trail educating visitors
about natural quiet
0.435 3.233 0.001
3. Signs are posted along the trail educating visitors
about natural quiet and asking visitors to limit
noise.
0.653 10.388 0.000
4. Signs are posted along the trail educating visitors
about natural quiet and asking visitors to limit
noise, and rangers are stationed along the trail to
limit visitor caused noise.
0.292 1.504 0.133
5. Signs are posted along the trail educating visitors
about natural quiet and asking visitors to limit
noise, and rangers are enforcing visitors to limit
their noise along the trail.
0.656 2.956 0.003
Closures
1. Trails are open during operating hours -- -- --
2. Trails are closed for one hour after dawn for the
morning breeding bird chorus
0.048 0.402 0.688
3. Trails are closed for one hour after dawn & one
hour before evening for the breeding bird chorus
-0.211 -1.480 0.140
ᵃ The sample sizes used to calculate the t-ratios are the number of the respondents for each of the group
Preferences for management
Results from Table 1 show that respondents in both the treatment and control
groups most preferred Management Strategy 3, signs posted along the trail educating
visitors about quiet and asking visitors to limit noise. The mean estimate is positive and
well above zero, indicating a strong preference (Mean=2.606 for treatment group and
1.973 for the control). The standard deviations for both of these mean scores are
significant and smaller than the mean. This indicates that a large portion of the
125
respondents indicated a strong, positive preference for this attribute. Large standard
deviation scores in Table 4-1 suggest variability in responses to specific attributes. For
example, in Management Strategy 5, the mean coefficient for the control group is 0.487
and the standard deviation is 2.618. This suggests heterogeneity in preferences across
respondents. A large proportion of the control group either had high or low utility for this
attribute.
The treatment group also showed a high preference for Management Strategy 4,
which is similar to Strategy 3, but rangers are stationed along the trail asking visitors to
be quiet. This means that visitors preferred forms of indirect management through
educational signs and ranger presence. Additionally, both groups had low utility scores
for option 5, signs are posted along the trail educating visitors about natural quiet &
asking visitors to limit noise, and rangers are enforcing visitors to limit their noise.
Option 5 is a more extreme form of direct management. In other words, if rangers were
enforcing visitors to limit noise, they would no longer have a choice for how they chose
to behave in the park. Direct management is considered a more “heavy” handed approach
to visitor use issues (Manning, 2011). The standard deviations for both groups were also
large and significant, indicating variability across respondents. Finally, none of the utility
scores for management attributes were negative. It is difficult to determine a logical
tradeoff because none of the attributes are attributed to a strong, negative utility.
Table 4-2 shows the comparison between preferences for choice attributes in the
treatment and control groups. There were significant differences between groups for
Management Scenarios 2, 3, and 5. Generally, respondents in the treatment group had a
higher preference for direct (signs are posted along the trail educating visitors about
126
natural quiet & asking visitors to limit noise, and rangers are enforcing visitors to limit
their noise ) and indirect management scenarios (signs posted along the trail educating
visitors about quiet and asking visitors to limit noise. ) than the control group. However,
there was not a significant difference between groups for Management Strategy 4, signs
are posted along the trail educating visitors about natural quiet and asking visitors to
limit noise, and rangers are stationed along the trail to limit visitor caused noise.
Preferences for Park Closure
Results from choice attributes related to park closure show relatively weak
marginal utility scores (Table 1). For both the treatment and control group, mean
coefficients were positive, but not significant, meaning they were not much different
from 0, indicating low utility. These results were not expected. Previous research
suggests that direct management strategies, such as park closures, would be very much
unwanted by respondents. As to say, respondents would not be supportive of park closure
in order to hear more natural sound or vice versa. Low mean coefficients and relatively
large, significant standard deviations suggest heterogeneity across respondents. In other
words, a large portion of respondents have either a more positive or more negative utility
for the closure attributes.
Moreover, there were no significant differences between treatment and control
groups in their preferences for closure attributes (Table 4-2). This indicates that the
closure attributes were inadequate indicators of choice preference. The closure attributes
yielded no sensible tradeoffs. This may be due to poor design or measurement errors.
127
Discussion
The purpose of this study was twofold, to understand tradeoffs visitors are willing
to make in order to hear natural sound and the differences in visitor preferences between
the treatment group (signs present asking visitors to maintain quiet) and the control group
(all signs are covered). The following section discusses study results, management
implications, and a direction for future research.
RQ1: What tradeoffs are visitors willing to make in order to hear natural sounds in Muir
Woods National Monument?
Based on results from these data, visitors who experienced both treatment and
control scenarios in the park preferred indirect forms of management. From these
findings we can predict that visitors will most likely prefer to see educational signs and
rangers that ask people to be quiet in order to hear a higher percent of natural sound.
Results from the random parameter logit model did not yield any clear tradeoffs. All
marginal utility scores were positive, suggesting respondents did not strongly dislike or
disapprove of any of the proposed management attributes. However, we are able to
interpret preferences and there was a clear strong, positive preference for educational
signage. Stack et al.’s (2011) study had similar findings related to educational signs. On
both treatment and control days, respondents rated the signs as highly acceptable.
Generally, park visitors find indirect forms of management to be desirable if they are
believed to be effective (Reviewed in Manning, 2011). Other studies have found that
visitors have a higher preference for indirect over direct management strategies (Lucas,
1983).
128
Most studies related to visitor attitudes towards management focus on the
backcountry setting. The current study, conducted at MUWO, is a frontcountry park. In
other words, MUWO is considered part of a more developed area and hiking trails are
relatively short. However, some studies have addressed visitors’ preferences in the
frontcountry. For example, Bullock & Lawson (2008), found that visitors to a popular
peak in Acadia National Park preferred direct forms of management for mitigating hiking
trail impacts. Riper, Manning, Monz, & Goonan (2011), had similar findings; park
visitors preferred direct forms of management. This is different from our results that
show visitors have less preference for rangers that enforce quiet, which is a form of direct
management. It’s possible that visitors generally have different attitudes towards
soundscape management when compared to managing trail impacts or crowding.
Attributes related to park closure were relatively weak and provided little
information related to visitor tradeoffs. This is likely linked to two existing conditions.
First, currently the park’s operating hours are from 8:00AM to 5:00PM. Essentially, this
management action already exists. Second, the majority of visitors were traveling from
San Francisco or other nearby areas and would
RQ2: Are preferences different for visitors in the treatment group (signs present asking
visitors to maintain quiet) vs. the control group (all signs are covered)?
Results from the comparison of preferences in management choice attributes
between the treatment and control groups were significant for 3 of the 5 scenarios. The
treatment group had significantly stronger marginal utility scores for these attributes. In
other words, the respondents who were exposed to “quiet” signs were more supportive of
129
management interventions than the group who was not exposed to signs. Another way of
interpreting these results is by understanding the environmental changes that were a result
of the two management strategies. In Stack et al.’s (2011) study, educational signs were
shown to lower the overall sound level of the park by 3 dB(A). Three doesn’t sound like a
significant change, however, if noise is lowered by 3 dB(A), the listening area for
humans is doubled. We can assume that the signs used in our study had a similar effect
and during treatment days, visitors’ opportunity to hear natural sounds were doubled
when compared to control days. It’s possible that preference for signs were higher
because visitors were experiencing a quieter, more enjoyable soundscape. They were also
able to experience the effectiveness of the signs.
Reducing visitor noise is perceived as an issue that visitors can immediately
address through their own control. Moreover, the feedback is instant. If you quiet
yourself and your party, you can instantly hear more natural sounds. Support for
soundscape management in the forms of signs could have been a preferred option for the
treatment group because they were experiencing the outcomes of a quieted acoustic
environment.
Management Implications
This study built on methods used by Stack et al. (2011), to test visitors’ response
to educational signage. Rather than testing visitors’ acceptability of signs as a form of
indirect management, our study used stated choice modeling to understand visitor
preferences and tradeoffs related to achieving a more natural soundscape. Respondents
130
who viewed signs and were potentially exposed to a quieter soundscape had a higher
preference for viewing educational signs than the control group. These findings suggest
visitors prefer educational signs asking other visitors to be quiet because they view them
as effective and the positive feedback is immediate. Managers as MUWO already use
signs in the Cathedral Grove section of the park. This area is a designated “quiet zone”.
Our results show a higher preference for educational signs, therefore managers should
consider using educational signs throughout the park. Other National Park units and
protected areas that are similar in size to MUWO and provide a frontcountry experience
should consider using educational signs to mitigate noise created by visitors.
Ultimately, respondents had positive preferences for both direct management
practices, such as ranger presence and enforcement, as well as, indirect (educational
signs). Moreover, there were no significant, negative preferences towards park closures.
Respondents’ support for natural sound management strategies suggest the overall value
visitors are placing on protecting natural sound conditions. Park managers can determine
which management approach is deemed acceptable by visitors or is the most effective in
quieting the soundscape. Similar to Park et al. (2008), different management techniques
can be tested using an experimental design.
Limitations and future research
While this study was useful for informing preferences related to soundscapes, it
does have some limitations that merit discussion. The results suggest that the stated
choice attributes related to closure were perhaps too similar to existing management
131
conditions. As mentioned earlier, the park’s hours are 8:00am to 5:00pm which are
similar to the closing times outlined in our attributes. This is perhaps why these attributes
did not yield any significant results. This study could have benefitted from investing
other management attributes that would alter the park soundscape. One attribute could
have been related to limiting the number of visitors allowed on the trail corridor at one
time. This would have been an example of a direct management strategy that would limit
noise, but also extremely limit visitor freedom.
The model used to analyze the stated choice data did not provide any clearly
interpreted tradeoffs. Future research should use an alternative approach to analyzing the
data in order to tease out any possible tradeoffs. A latent class logit model or additional
modeling strategy that accounts for differences among respondent demographics will be
tested.
Conclusion
This study is the first of its kind to investigate visitor preferences related to
soundscapes. Our results show that visitors prefer educational signs and interference from
management to experience a quieter soundscape. Additionally, the experimental design of
the study determined that the presence of educational sings had a significant influence on
choice preferences related to soundscape management. The benefits of experiencing
natural sounds are vast. Management implications from this study can be applied to parks
and protected areas, especially parks near large urban centers where a break from loud,
man-made noise is most needed.
132
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mammal. Behavioral Ecology, 27(5), 1370–1375.
https://doi.org/10.1093/beheco/arw058
Shavelson, R. J. (2004). Editor’s Preface to Lee J. Cronbach’s “My Current Thoughts on
Coefficient Alpha and Successor Procedures”Lee J. Cronbach 1916-2001.
Educational and Psychological Measurement, 64(3), 389–390.
https://doi.org/10.1177/0013164404264117
Shelby, B., Vaske, J. J., & Donnelly, M. P. (1996). Shelby et al (1996) - Norms,
standards _ natural resources.pdf.
Stack, D. W., Peter, N., Manning, R. E., & Fristrup, K. M. (2011). Reducing visitor noise
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Stankey, G. H., Cole, D. N., Lucas, R. C., Petersen, M. E., & Frissell, S. S. (1984). The
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Taff, D., Newman, P., Lawson, S. R., Bright, A., Marin, L., Gibson, A., & Archie, T.
(2014). The role of messaging on acceptability of military aircraft sounds in Sequoia
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https://doi.org/10.3390/su9112088
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Chapter 5
Conclusion and Implications
The purpose of this dissertation was to explore different methodologies for measuring
visitor experiences with the acoustic environment in National Parks. The first paper assessed the
relationship between one’s home sound level and their interpretation of soundscapes at Muir
Woods National Monument. The second paper utilized a large suite of sound clips to estimate
visitors’ threshold for propeller aircraft noise at Denali National Park and Preserve. And the third
paper analyzed tradeoffs visitors to Muir Woods National Monument are willing to make in order
to experience a more natural soundscape. This final chapter will summarize the findings from
earlier chapters and interpret the overall management implications of this dissertation.
Summary of Findings and Implications
This dissertation contains three independent manuscripts related to understanding and
measuring soundscapes in relation to visitor experience. Six separate research questions were
examined. This section will summarize the results and implications related to each question.
Q1: What factors influence visitors’ perception of the soundscape in Muir Woods
National Monument?
A multiple linear regression model was used to determine variables that relate to
visitors’ perception of the soundscape in Muir Woods National Monument. The
dependent variable, pleasantness, was used to measure overall interpretation of the sound
condition at the park. Results from the regression analysis determined factors related to
soundscape pleasantness included: the ability to hear natural sounds during the park visit,
sensitivity to noise, and the mean sound level of the respondents’ home zip code.
145
Q2: How does the sound level of visitors’ home zip code area influence their park
soundscape perception?
Spatial analysis tools were used to derive the average sound level of survey
respondents’ home zip code. The multiple regression model mentioned above suggest the
sound level of individuals’ home zip code significantly contributes to visitors’ perception
of the pleasantness of the parks’ soundscape. The model revealed a negative relationship;
meaning that as the mean sound level of the zip code increased, the rating of soundscape
pleasantness decreased.
Q3: How can researchers best inform the development of thresholds for soundscape
quality using dose response methodology?
To better control for noise exposure, survey respondents in the field listened to five audio
clips of varying levels of propeller aircraft, chosen randomly from a suite of 36 clips. The method
of randomizing the order and level of the audio clips improved the validity of visitors’ response to
noise. General linear mixed models were used to predict visitors’ response to the varying levels of
propeller aircraft noise. The models were able to account for random effects and other variables
that contributed to the final models. This methodology provided a more rigorous and accurate
understanding of anthropogenic sound sources that relate to thresholds for noise exposure.
Q4: What factors influence visitors’ perception of overflight audio clips?
Results from generalized mixed linear models showed that visitors’ response to
sound depends largely on the loudness of specific noise sources. Sound level (LAeq30s)
was an important factor in all four regression models. Clip sequence, or the order in
which audio clips were played was another important factor in predictive models which
further justifies the importance of playing a random order of varying levels of audio clips.
146
Q5: What tradeoffs are visitors willing to make in order to hear natural sounds in
Muir Woods National Monument?
The stated choice survey did not yield any clear tradeoffs related to soundscape
management. However, our results did indicate strong, positive preferences for direct
management strategies in the form of educational signs. Our study findings suggest that
visitors have a higher preference for experiencing a park with signs asking visitors to be
quiet, than a park with no soundscape management.
Q6: Are preferences different for visitors in the treatment group (signs present
asking visitors to maintain quiet) vs. the control group (all signs are covered)?
Our study yielded significant differences in management strategies between
treatment and control groups. The treatment group had a stronger preference for attributes
that aimed to quiet park visitors using educational signs and ranger presence. The
difference between groups could be a result of the treatment’s effectiveness in quieting
visitors. We can assume based on empirical evidence that the park was quieter during
treatment periods. Thus, the presence of educational signs increased visitors’ preference
for a quieter soundscape and the presence of indirect management such as signs.
Implications
The three separate studies presented in this dissertation explore different and innovative
methodological approaches to understanding soundscapes. While these studies were conducted at
either Denali National Park and Preserve or Muir Woods National Monument, management
implications can be applied to similar parks. The findings from these studies provide park
147
managers with a holistic approach to protecting soundscapes for the purpose of positive visitor
experiences.
Home Sound Level Influences Soundscape Perception
The findings from the second chapter of this dissertation suggest the level of sound
people are exposed to in their home environment contributes to their perception of the park
soundscape. While these findings don’t have a specific impact on soundscape management, they
do contribute to the existing body of social science literature that examines human response to
sound. Factors other than attitudes, beliefs, and values can play in important role in the variability
of individuals’ response to sound.
Our results do suggest the importance of quieting frontcountry parks similar to Muir
Woods National Monument. It’s possible that respondents in our study from louder areas found
the soundscape at Muir Woods to be less pleasant as a result of increased noise levels. For park
visitors to receive potential benefits of natural sound, an effort towards quieting frontcountry
parks is suggested.
Assessing Large Variety of Sound Levels Improves Validity of Soundscape Thresholds
Previous studies have used a small range of audio clips and average ratings of annoyance
to measure visitor thresholds for anthropogenic sound sources. The third chapter of this
dissertation identified potential thresholds for propeller aircraft using a large suite of varying
audio clips. Additionally, regression models that accounted for variability amongst individuals
was used to predict sound levels that were deemed annoying or unacceptable. This study was
148
conducted in Denali National Park and Preserve’s frontcountry area, but this method can be
applied to other parks and protected areas where anthropogenic noise is of concern.
Park Visitors Prefer Soundscape Management
The fourth chapter of this dissertation identified visitor preferences for soundscape
management at Muir Woods National Monument. Overall, visitors preferred forms of indirect
soundscape management in the form of educational signs. We also compared scores between the
treatment and control groups. Because visitors in the group that were exposed to signs had
significantly higher utility ratings for attributes with educational signs, it’s possible that this
group experienced the benefits of signs (i.e. a quieter park). Other parks and protected areas
where visitor caused noise is prevalent can use these findings to empirically justify the need for
educational signs that aim to quiet visitors.
Conclusion
Together, the three studies presented in this dissertation aimed to explore different
methodologies for measuring visitor experiences with the acoustic environment in National Parks.
While the methods used in these studies were innovative and will be useful to park managers, the
ultimate take away is that natural sounds are important. Results from the first study indicate that
visitors’ home sound level does in fact influence their perception of the park soundscape. In the
second study, potential thresholds for aircraft overflights were measured. Again, sound level was
an important factor in regression models. In the final study, we found that visitors prefer
soundscape management and educational signs that aim to quiet the park. These findings
highlight the value that visitors are placing on protecting natural sound conditions. In conclusion,
149
the simple vibration of sound, is an important part of the national park experience. Both park
managers and social scientists should continue to understand the human experience in relation to
soundscapes so that future generations can enjoy the benefits of natural sound.
Appendix A
Chapter’s 2 &4 Survey Instrument
Muir Woods National Monument
Visitor Study (A)
Park Permit Number: MUWO-2016-SCI-0001
Survey Information and Instructions:
The focus of this study is to better understand visitor preferences regarding the management of soundscapes within Muir
Woods National Monument
Your participation in the study is voluntary. There are no penalties for not answering some or all questions, but because
each participant will represent many others who will not be included in the study, your input is extremely important. The answers
you provide will remain anonymous. Our results will be summarized so that the answers you provide cannot be associated with
you or anyone in your group or household.
Pennsylvania State University thanks you for your assistance.
We estimate that it will take about 10 minutes to complete and return this questionnaire. You may send comments concerning the burden estimates
or any aspect of this information collection to: Dr. Peter Newman, Department Head & Professor, Recreation, Park and Tourism Management, 801
Ford Building, University Park, PA 16802, Penn State University, 814-863-7849 (phone) or [email protected] (email).
151
1. Visitors have different reasons for visiting Muir Woods National Monument. Please rate the importance
of each of the following reasons for your visit to Muir Woods National Monument today. Please mark
only one response for each item. Importance… Not
Relevant
Not at all
Important
Slightly
Important
Moderately
Important
Very
Important
Extremely
Important
To experience a sense of connection
with nature □ □ □ □ □ □
To experience the diversity of the
natural world □ □ □ □ □ □
To enjoy the natural quiet and sounds
of nature □ □ □ □ □ □
To give my mind a rest □ □ □ □ □ □
To get away from the usual demands
of life □ □ □ □ □ □
To get away from the noise back
home □ □ □ □ □ □
To develop your skills and abilities □ □ □ □ □ □
To improve your skills □ □ □ □ □ □
To do something with your family □ □ □ □ □ □
To be with friends □ □ □ □ □ □
To experience wildlife in nature □ □ □ □ □ □
To photograph wildlife □ □ □ □ □ □
Seeing the redwoods □ □ □ □ □ □
Appreciating the scenic beauty □ □ □ □ □ □
Experiencing solitude □ □ □ □ □ □
Getting some exercise □ □ □ □ □ □
Learning about nature □ □ □ □ □ □
Enjoying the peace and quiet □ □ □ □ □ □
Hearing the sounds of nature □ □ □ □ □ □
152
2. Based on your experience today, about how many different types of birds would you say are in the trail
corridor? Please mark one response.
□ 0-3 different types of birds
□ 4-7 different types of birds
□ 8-11 different types of birds
□ 12-15 different types of birds
□ More than 15 different types of birds
3. If you heard bird song today, how would you rate the diversity of the bird song chorus? Please mark one
response.
Not at All
Diverse
A Little
Diverse
Moderately
Diverse
Highly
Diverse
Extremely
Diverse I did not hear bird song
□ □ □ □ □ □
153
4. Visitors hear a lot of sounds, including natural sounds and human-made sounds. Based on your experience
today, how would you rate the pleasantness of the soundscape? Please mark one response.
Very
Unpleasant
Moderately
Unpleasant
Slightly
Unpleasant
Slightly
Pleasant
Moderately
Pleasant
Very
Pleasant
□ □ □ □ □ □
5. Based on your experience today, how well were you able to hear natural sounds? Please mark one response.
□ Almost always clearly without interference from human-made sound
□ Usually clearly without interference from human-made sound
□ Sometimes clearly without interference from human-made sound
□ Usually with interference from human-made sound
□ Almost always with interference from human-made sound
154
In this section we would like know your opinion about a series of hypothetical management scenarios within Muir
Woods National Monument. There are 8 questions and each question has two scenarios. Please read both scenarios
and then select the one that you would most prefer to experience during a visit to the Muir Woods National
Monument.
6a. Which description below would best depict your most preferred experience in Muir Woods National
Monument?
☐ Scenario 1
☐ Scenario 2
■ You can hear natural sounds (e.g. birdsong, small
mammals) some of the time (about 25% of the
time)
■ You can rarely hear natural sounds (e.g. birdsong, small
mammals) (about 5% of the time)
■ Signs are posted along the trail educating visitors
about natural quiet & asking visitors to limit noise
■ Signs are posted along the trail educating visitors about
natural quiet
■ Trails are closed for one hour after dawn & one
hour before evening for the breeding bird chorus
■ Trails are open during operating hours
155
6b. Which description below would best depict your most preferred experience in Muir Woods
National Monument?
☐ Scenario 1
☐ Scenario 2
■ You can hear natural sounds (e.g. birdsong,
small mammals) most of the time (about 75%
of the time)
■ You can hear natural sounds (e.g. birdsong,
small mammals) some of the time (about 25%
of the time)
■ No signs are posted along the trail about natural
quiet
■ Signs are posted along the trail educating
visitors about natural quiet & asking visitors
to limit noise, and rangers are stationed along
the trail to limit visitor caused noise
■ Trails are closed for one hour after dawn for the
morning breeding bird chorus
■ Trails are open during operating hours
156
6c. Which description below would best depict your most preferred experience in Muir Woods
National Monument?
☐ Scenario 1
☐ Scenario 2
■ You can hear natural sounds (e.g. birdsong,
small mammals) some of the time (about 25%
of the time)
■ You can hear natural sounds (e.g. birdsong,
small mammals) about half of the time (about
50% of the time)
■ Signs are posted along the trail educating
visitors about natural quiet & asking visitors to
limit noise
■ Signs are posted along the trail educating
visitors about natural quiet & asking visitors
to limit noise, and rangers are enforcing
visitors to limit their noise along the trail
■ Trails are closed for one hour after dawn for the
morning breeding bird chorus
■ Trails are closed for one hour after dawn &
one hour before evening for the breeding bird
chorus
157
6d. Which description below would best depict your most preferred experience in Muir Woods
National Monument?
☐ Scenario 1
☐ Scenario 2
■ You can rarely hear natural sounds (e.g.
birdsong, small mammals) (about 5% of the
time)
■ You can hear natural sounds (e.g. birdsong,
small mammals) some of the time (about 25%
of the time)
■ No signs are posted along the trail about natural
quiet
■ Signs are posted along the trail educating
visitors about natural quiet & asking visitors
to limit noise, and rangers are enforcing
visitors to limit their noise along the trail
■ Trails are open during operating hours ■ Trails are open during operating hours
158
6e. Which description below would best depict your most preferred experience in Muir Woods
National Monument?
☐ Scenario 1
☐ Scenario 2
■ You can rarely hear natural sounds (e.g.
birdsong, small mammals) (about 5% of the
time)
■ You can rarely hear natural sounds (e.g.
birdsong, small mammals) (about 5% of the
time)
■ Signs are posted along the trail educating
visitors about natural quiet & asking visitors to
limit noise, and rangers are enforcing visitors to
limit their noise along the trail
■ Signs are posted along the trail educating
visitors about natural quiet & asking visitors
to limit noise, and rangers are stationed along
the trail to limit visitor caused noise
■ Trails are closed for one hour after dawn for the
morning breeding bird chorus
■ Trails are closed for one hour after dawn for
the morning breeding bird chorus
159
6f. Which description below would best depict your most preferred experience in Muir Woods
National Monument?
☐ Scenario 1
☐ Scenario 2
■ You can hear natural sounds (e.g. birdsong,
small mammals) most of the time (about 75%
of the time)
■ You can hear natural sounds (e.g. birdsong,
small mammals) most of the time (about 75%
of the time)
■ Signs are posted along the trail educating
visitors about natural quiet
■ Signs are posted along the trail educating
visitors about natural quiet & asking visitors
to limit noise, and rangers are stationed along
the trail to limit visitor caused noise
■ Trails are closed for one hour after dawn & one
hour before evening for the breeding bird
chorus
■ Trails are closed for one hour after dawn for
the morning breeding bird chorus
160
6g. Which description below would best depict your most preferred experience in Muir Woods
National Monument?
☐ Scenario 1
☐ Scenario 2
■ You can hear natural sounds (e.g. birdsong,
small mammals) about half of the time (about
50% of the time)
■ You can hear natural sounds (e.g. birdsong,
small mammals) about half of the time (about
50% of the time)
■ Signs are posted along the trail educating
visitors about natural quiet & asking visitors to
limit noise, and rangers are enforcing visitors to
limit their noise along the trail
■ No signs are posted along the trail about
natural quiet
■ Trails are open during operating hours ■ Trails are closed for one hour after dawn for
the morning breeding bird chorus
161
6h. Which description below would best depict your most preferred experience in Muir Woods
National Monument?
☐ Scenario 1
☐ Scenario 2
■ You can hear natural sounds (e.g. birdsong,
small mammals) about half of the time (about
50% of the time)
■ You can hear natural sounds (e.g. birdsong,
small mammals) most of the time (about 75%
of the time)
■ No signs are posted along the trail about natural
quiet
■ Signs are posted along the trail educating
visitors about natural quiet & asking visitors
to limit noise
■ Trails are closed for one hour after dawn for the
morning breeding bird chorus
■ Trails are closed for one hour after dawn for
the morning breeding bird chorus
162
7. The following list suggests kinds of reasons you might have deliberately chosen to limit the amount of noise
you made in the park. For each of the reasons below, please indicate the extent to which you agree or disagree
that the reason applies to you. Please mark only one response for each item.
Strongly
disagree
Disagree Neutral Agree Strongly
agree
I was afraid I would be reprimanded if I made too
much noise. □ □ □ □ □
I was afraid I would be fined if I made too much
noise. □ □ □ □
I was afraid other members of my group would
think poorly of me if I made too much noise. □ □ □ □ □
I was afraid other visitors in general would think
poorly of me if I made too much noise. □ □ □ □ □
It’s not fair to other visitors for me to make a lot of
noise. □ □ □ □ □
I feel better about myself when limiting the amount
of noise I make. □ □ □ □ □
8. Which of the following best describes where you went in Muir Woods today? Please mark one response.
□I only walked on the paved/boardwalk trails on the canyon floor.
□I walked on the paved/boardwalk trail on the canyon floor and hiked on some of the
unpaved trails on the slopes of the canyon.
163
9. Please check the box corresponding with how well you agree or disagree. Please mark only one response for
each item.
Strongly
Disagree
Disagree Slightly
Disagree
Slightly
Agree
Agree Strongly
Agree
I am sensitive to noise.
□ □ □ □ □ □
I find it hard to relax in a place that's noisy. □ □ □ □ □ □
I get mad at people who make noise that
keeps me from falling asleep or getting
work done.
□ □ □ □ □ □
I get annoyed when my neighbors are noisy. □ □ □ □ □ □
I get used to most noises without much
difficulty. □ □ □ □ □ □
10. How crowded did you feel on the trail today? Please select one number.
1 2 3 4 5 6 7 8 9
Not crowded at all Slightly crowded Moderately crowded Extremely crowded
11. Including this visit, how many times have you visited Muir Woods National Monument?
Approximate number of visits: _____________
12. Approximately how many hours did you spend in Muir Woods National Monument today?
Approximately _____________hours
164
13. How many adults and how many children were in your personal group (spouse, family, friends) during this
trip to Muir Woods National Monument today? Please provide a number.
# of Adults (Age 16 or older) _______ # of Children (Age 15 or younger) _______
14. How would you describe your group?
□ Alone
□ Family
□ Friends
□ Family and Friends
□ Organized Group (e.g., club, educational group)
□ Commercial tour group
□ Other (Please specify):______________________
15. What is your gender?
Male Female
16. In what year were you born?
Year Born: __________________
17. Do you live in the United States?
Yes (What is your zip code? __________)
No (What country do you live in? ______________________________
165
18. What is the highest level of formal education you have completed? Please mark only one response. Some high school
High school graduate or GED
Some college, business or trade school
College, business or trade school graduate
Some graduate school
Master’s, doctoral or professional degree
Thank you for your assistance in completing this survey.
Start here
Appendix B
Chapter 3 Survey Instrument
Denali National Park and Preserve
Visitor Study B
Sound Clip Survey
PAPERWORK REDUCTION ACT STATEMENT: The National Park Service is authorized by the NPS
Research Mandate (54 USC 100702) to collect this information. This information will be used by park
managers to understand visitors’ perceptions of sounds in the front-country of Denali National Park and
Preserve. Responses to this request are voluntary and anonymous. Your name will never be associated with
your answers, and all contact information will be destroyed when the data collection is concluded. No action
may be taken against you for refusing to supply the information requested. An agency may not conduct or
sponsor, and a person is not required to respond to, a collection of information unless it displays a currently
valid OMB control number and expiration date.
BURDEN ESTIMATE statement: Public reporting burden for this form is estimated to average 15 minutes
per response. Direct comments regarding the burden estimate or any other aspect of this form to: Denali
National Park and Preserve, PO Box 9, Denali Park, AK 99755.
167
1. Is this your first visit to Denali?
YES ☐ (If YES, move on to #2) NO ☐
If NO, Approximately how many times have you visited Denali?
Times before ___________ (approximate)
OR
☐ Don’t know/not sure
2. How important was it that these visits to Denali’s developed area or front country provide you with
the opportunity to...? Mark "Not relevant" if an aspect was not relevant for this visit.
Importance
Not
Relevant
(0)
Not at all
Important
(1)
Slightly
Important
(2)
Moderately
Important
(3)
Very
Important
(4)
Extremely
Important
(5)
Appreciate the history and
cultural significance of the site (0) (1) (2) (3) (4) (5)
View the natural scenery (0) (1) (2) (3) (4) (5)
Experience a feeling of
calmness, peace, or tranquility (0) (1) (2) (3) (4) (5)
Experience a sense of adventure
or challenge (0) (1) (2) (3) (4) (5)
Enjoy the natural quiet and
sounds of nature (0) (1) (2) (3) (4) (5)
168
3. How much did man-made sounds interfere with your enjoyment during your time in Denali’ front
country? (Please select one)
Much less than
I expected
Less than I
expected
About as much as I
expected
More than I
expected
Much more than
I expected
1 2 3 4 5
4. What man-made sounds interfered the most with your enjoyment? (Please describe)
___________________________________________________________________
5. Instructions
For the next set of questions, we would like you to listen to five short recordings of sounds that are typically
heard in Denali’s front-country.
Please place the headphones on your head. We will ask you to listen to five brief recordings of sounds. As you
listen to each recording, imagine how you would have felt if you had heard the sounds in the recording during
your visit to Denali’s front country (only).
The survey administrator will play each sound clip for you. Please listen to each recording in its entirety; then
answer the survey questions that relate to each recording.
169
RECORDING #1
6. How acceptable or unacceptable would the aircraft sounds in recording #1 have been if you had
heard them during this visit to Denali while in the front country?
Unacceptable Acceptable
Extremely Very Moderately Slightly Neutral Slightly Moderately Very Extremely
(-4) (-3) (-2) (-1) (0) (+1) (+2) (+3) (+4)
7. How pleased or annoyed would you have been by aircraft sounds in recording #1 if you had heard
them during this visit to Denali while in the front country?
Annoyed Pleased
Extremely Very Moderately Slightly Neutral Slightly Moderately Very Extremely
(-4) (-3) (-2) (-1) (0) (+1) (+2) (+3) (+4)
Pause: Keep your headphones on and wait for the survey administrator to play recording #2
RECORDING #2
8. How acceptable or unacceptable would the aircraft sounds in recording #2 have been if you had
heard them during this visit to Denali while in the front country?
Unacceptable Acceptable
Extremely Very Moderately Slightly Neutral Slightly Moderately Very Extremely
(-4) (-3) (-2) (-1) (0) (+1) (+2) (+3) (+4)
170
9. How pleased or annoyed would you have been by aircraft sounds in recording #2 if you had heard
them during this visit to Denali while in the front country?
Annoyed Pleased
Extremely Very Moderately Slightly Neutral Slightly Moderately Very Extremely
(-4) (-3) (-2) (-1) (0) (+1) (+2) (+3) (+4)
Pause: Keep your headphones on and wait for the survey administrator to play recording #3
RECORDING #3
10. How acceptable or unacceptable would the aircraft sounds in recording #3 have been if you had
heard them during this visit to Denali while in the front country?
Unacceptable Acceptable
Extremely Very Moderately Slightly Neutral Slightly Moderately Very Extremely
(-4) (-3) (-2) (-1) (0) (+1) (+2) (+3) (+4)
11. How pleased or annoyed would you have been by aircraft sounds in recording #3 if you had heard
them during this visit Denali while in the front country?
Annoyed Pleased
Extremely Very Moderately Slightly Neutral Slightly Moderately Very Extremely
(-4) (-3) (-2) (-1) (0) (+1) (+2) (+3) (+4)
Pause: Keep your headphones on and wait for the survey administrator to play recording #4
171
RECORDING #4
12. How acceptable or unacceptable would the aircraft sounds in recording #4 have been if you had
heard them during this visit to Denali while in the front country?
Unacceptable Acceptable
Extremely Very Moderately Slightly Neutral Slightly Moderately Very Extremely
(-4) (-3) (-2) (-1) (0) (+1) (+2) (+3) (+4)
13. How pleased or annoyed would you have been by aircraft sounds in recording #4 if you had heard
them during this visit to Denali while in the front country?
Annoyed Pleased
Extremely Very Moderately Slightly Neutral Slightly Moderately Very Extremely
(-4) (-3) (-2) (-1) (0) (+1) (+2) (+3) (+4)
Pause: Keep your headphones on and wait for the survey administrator to play recording #5
RECORDING #5
14. How acceptable or unacceptable would the aircraft sounds in recording #5 have been if you had
heard them during this visit to Denali while in the front country?
Unacceptable Acceptable
Extremely Very Moderately Slightly Neutral Slightly Moderately Very Extremely
(-4) (-3) (-2) (-1) (0) (+1) (+2) (+3) (+4)
172
15. How pleased or annoyed would you have been by aircraft sounds in recording #5 if you had heard them
during this visit to Denali while in the front country?
Annoyed Pleased
Extremely Very Moderately Slightly Neutral Slightly Moderately Very Extremely
(-4) (-3) (-2) (-1) (0) (+1) (+2) (+3) (+4)
Instructions: Now we would like to know how often you think it’s acceptable to hear aircraft sounds while in
Denali’s front-country. Please listen to a short recording of both natural and aircraft sounds, and then answer
the questions that follow.
RECORDING #6
16. How acceptable or unacceptable would the aircraft sound in recording #6 be if it occurred for the
following amounts of time per hour during your time in Denali’s front country? Provide an answer
for each time period.
Unacceptable Acceptable
Minutes
Per
Hour
Extremely
(-4)
Very
(-3)
Moderately
(-2)
Slightly
(-1)
Neutral
(0)
Slightly
(+1)
Moderately
(+2)
Very
(+3)
Extremely
(+4)
3 (-4) (-3) (-2) (-1) (0) (+1) (+2) (+3) (+4)
9 (-4) (-3) (-2) (-1) (0) (+1) (+2) (+3) (+4)
15 (-4) (-3) (-2) (-1) (0) (+1) (+2) (+3) (+4)
30 (-4) (-3) (-2) (-1) (0) (+1) (+2) (+3) (+4)
173
17. How frequently would you prefer to hear small airplanes as you heard in recording #6 while in
Denali’s front country? Please enter a number or select the checkbox.
No more than ______ small airplanes in an hour
OR
☐ I would prefer to never hear small airplanes
18. How acceptable or unacceptable would the aircraft sounds in recording #6 be if you heard it the
following number of times per day during your time in Denali’s front country? Provide an answer
for each number.
Unacceptable Acceptable
Flights
per day
Extremely
(-4)
Very
(-3)
Moderately
(-2)
Slightly
(-1)
Neutral
(0)
Slightly
(+1)
Moderately
(+2)
Very
(+3)
Extremely
(+4)
1 (-4) (-3) (-2) (-1) (0) (+1) (+2) (+3) (+4)
10 (-4) (-3) (-2) (-1) (0) (+1) (+2) (+3) (+4)
25 (-4) (-3) (-2) (-1) (0) (+1) (+2) (+3) (+4)
50 (-4) (-3) (-2) (-1) (0) (+1) (+2) (+3) (+4)
100 (-4) (-3) (-2) (-1) (0) (+1) (+2) (+3) (+4)
19. How frequently could you hear small airplanes as you heard in recording #6 before you would no
longer visit Denali’s front country? Please enter a number or select the checkbox.
No more than ______ overflights in a day.
OR
I would visit Denali’s front-country regardless of how frequently small airplanes or helicopters are
heard.
174
20. Besides the recordings you just listened to, did you HEAR aircraft during your time in Denali?
☐ Yes (If yes move on to #21)
☐ No (If no, move on to #22)
21. During this visit to Denali how much did noise from aircraft annoy you?
Annoy
Not at all Slightly Moderately Very Extremely
☐ ☐ ☐ ☐ ☐
22. Have you ever taken a commercial flightseeing tour over Denali or any other park? Please check all
that apply.
YES, I have taken a commercial flightseeing tour over Denali ☐
YES, I have taken a commercial flightseeing tour over another
park ☐
NO, I have never taken a commercial flightseeing tour over a
park ☐
23. Are you interested in taking a commercial flightseeing tour over Denali?
☐ YES ☐ NO ☐ Don’t Know/Not Sure
175
24. Have you ever taken an air taxi over Denali or any other park? Please check all that apply.
YES, I have taken an air taxi over Denali ☐
YES, I have taken an air taxi over another park ☐
NO, I have never taken an air taxi over a park ☐
25. On this trip, did you and your personal group camp inside Denali?
YES
If yes, where did you camp? _____________________________________
NO, day use only
26. How many adults and how many children were in your personal group (spouse, family, friends)
during this visit to Denali? Please provide a number.
Number of Adults (Age 16 or Older) _______
Number of Children (Age 15 or Younger) _______
27. On this visit, how long did you and your personal group stay at Denali? Please list hours or days
below.
Number of hours, if less than 24 _______
or
Number of days, if 24 hours or more _______
28. Were you or your personal group part of some larger commercial, educational, or other organized
group of visitors? ☐ YES ☐ NO
176
29. What is your gender? ☐ Female Male
30. In what year were you born? Year born:___________
31. Do you live in the United States?
YES (What is your zip code? __________)
NO (What country do you live in? ______________________________)
32. What is the highest level of formal education you have completed? (Check one.)
Some high school (6)
High school graduate or GED (5)
Some college, business or trade school (4)
College, business or trade school graduate (3)
Some graduate school (2)
Master’s, doctoral or professional degree (1)
33. Are you Hispanic or Latino? ☐ YES ☐ NO
34. What is your race? (Check all that apply.)
American Indian or Alaska Native (6)
Asian (5)
Black or African American (4)
Native Hawaiian (3)
Pacific Islander other than Native Hawaiian (2)
White (1)
Denali National Park and Preserve and Penn State University both thank you for your assistance.
VITA
Lauren Abbott Ferguson EDUCATION
Ph.D. 2018 The Pennsylvania State University, University Park, Pennsylvania
Recreation, Park, and Tourism Management
Human Dimensions of Natural Resources and the Environment (Dual-Degree)
M.S. 2015 The Pennsylvania State University, University Park, Pennsylvania
Recreation, Park, and Tourism Management
Thesis Title: The Influence of Natural Sounds on Attention Restoration
B.S. 2008 Colorado State University, Fort Collins, Colorado
Natural Resource Recreation and Tourism
Environmental Communication Concentration
SELECTED PUBLICATIONS
Francis, C. D., Newman, P., Taff B. D., Crow, W., Monz, C. A., Levenhagen, M., Petrelli, A. R.,
Abbott, C. L., Newton, J., Burson, S., Cooper, C. B., Fristrup, K. M., McClure, C. J. W.,
Mennitt, D., Giamellaro, & M., Barber, J. R. (2017). Acoustic Environments Matter:
Synergistic Benefits to Humans and Wildlife. Ecology Letters.
Abbott, C. L., Taff, B. D., Newman, P., Benfield, A. B., & Mowen, A. J. (2016). The Influence
of Natural Sounds on Attention Restoration. Journal of Park and Recreation
Administration 34(3), 5-15. DOI: 10.18666/JPRA-2016-V34-I3-6893
Abbott, C. L., Taff, B. D., Newman, P, & Burson, S. (2016). Exploring Vertical Wilderness in
the Acoustic Environment. Submitted to National Park Service, Washington D.C.
SELECTED CONFERENCE PRESENTATIONS
Abbott, C.L., Newman, P., Taff, B.D., Burson, S. (2017, April). The effects of natural and
anthropogenic sounds on climber experiences in Grand Teton National Park.
Presented at the meeting of the 19th annual George Wright Society Conference,
Norfolk, VA.
Abbott, L.C., Newman, P., Taff, B.D., & Blanford, J. (2016, November). Understanding
soundscape perceptions in national parks, Presented at Penn State GIS Day, University
Park, PA.
Abbott, C. L., Newman, P., Taff, B. D., Burson, S. (2016, October). Exploring Vertical
Wilderness in the Acoustic Environment. Presented at the meeting of the 13th annual
Biennial Scientific Conference on the Greater Yellowstone Ecosystem, Jackson, WY.
TEACHING EXPERIENCE
2017 Instructor- Research and Evaluation in Recreation and Parks (RPTM 433), The
Pennsylvania State University
2018 Instructor- Grantsmanship, Eval, & Research Methods (RMP 724), University of
New Hampshire