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Capacity, Pressure, Demand, and Flow:
A conceptual framework for analyzing ecosystem service provision and delivery
Amy M. Villamagnaa*, Paul L. Angermeierb, Elena M. Bennettc
a Department of Fish and Wildlife Conservation, Virginia Tech, Blacksburg, VA 24061-
0321, USA *Corresponding author, [email protected] ; b U.S. Geological Survey, Virginia
Cooperative Fish and Wildlife Research Unit1, Virginia Tech, Blacksburg, VA 24061-
0321, USA [email protected]; c Department of Natural Resource Sciences and McGill School
of Environment, McGill University, Montreal, Quebec, CANADA
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ABSTRACT
Ecosystem services provide an instinctive way to understand the trade-offs associated with
natural resource management. However, despite their apparent usefulness, several hurdles have
prevented ecosystem services from becoming deeply embedded in environmental decision-
making. Ecosystem service studies vary widely in focal services, geographic extent, and in
methods for defining and measuring services. Dissent among scientists on basic terminology and
approaches to evaluating ecosystem services create difficulties for those trying to incorporate
ecosystem services into decision-making. To facilitate clearer comparison among recent studies,
we provide a synthesis of common terminology and explain a rationale and framework for
distinguishing among the components of ecosystem service delivery, including: an ecosystem’s
capacity to produce services; ecological pressures that interfere with an ecosystem’s ability to
provide the service; societal demand for the service; and flow of the service to people. We
discuss how interpretation and measurement of these four components can differ among
provisioning, regulating, and cultural services. Our flexible framework treats service capacity,
ecological pressure, demand, and flow as separate but interactive entities to improve our ability
to evaluate the sustainability of service provision and to help guide management decisions. We
consider ecosystem service provision to be sustainable when demand is met without decreasing
capacity for future provision of that service or causing undesirable declines in other services.
When ecosystem service demand exceeds ecosystem capacity to provide services, society can
choose to enhance natural capacity, decrease demand and/or ecological pressure, or invest in a
technological substitute. Because regulating services are frequently overlooked in environmental
assessments, we provide a more detailed examination of regulating services and propose a novel
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method for quantifying the flow of regulating services based on estimates of ecological work.
We anticipate that our synthesis and framework will reduce inconsistency and facilitate
coherence across analyses of ecosystem services, thereby increasing their utility in
environmental decision-making.
KEYWORDS: ecological pressure, ecosystem services, inventory and assessment, regulating
services, service capacity, service demand, service flow
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1. Introduction
Ecosystem services (ES) have great potential to influence environmental decisions
because they link ecosystem functions and conditions to anthropocentric interests that resonate
with a broad spectrum of people. ES provide new currencies, often not represented in markets,
for understanding the tradeoffs associated with natural resource management (Raudseppe-Hearne
et al., 2010; Chan et al., 2012). Because of this, efforts to assess and inventory ES have been
extensive (Peterson et al., 2003; MA, 2005; Tallis and Polasky, 2011; Burkhard et al., 2012);
however, several hurdles have prevented ES from becoming deeply embedded in environmental
decision-making (Daily et al., 2009; de Groot et al., 2010). However, a fundamental hurdle in
using ES in decision-making is the inconsistency with which scientists have conceptualized
delivery of ES to society (Tallis et al., 2012). Recent strides towards greater consideration of ES
have been made in the European Union (TEEB, 2010; European Commission, 2011; Hauck et
al., 2013); however, use of the ES concepts in policy-making remains limited (Fisher et al.,
2009) and many questions persist over how ES relate to each other, how ecosystems produce
services, how to consistently quantify ES flows, and how changes in landscapes are likely to
affect future delivery of ES (Chan et al., 2006; Carpenter et al., 2009; de Groot et al., 2010;
Hauck et al., 2013).
Despite real differences, few researchers distinguish among the capacity of an ecosystem
to produce a service, actual production or use of that service, societal demand for that service,
and the natural and anthropogenic pressures on the service (Burkhard et al., 2012; Nedkov and
Burkhard, 2012; van Oudenhoven et al., 2012). For example, the capacity of an ecosystem to
generate services differs from the actual services delivered to society. A farm may produce less
food than it could under different management choices, or a wetland may have greater capacity
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to filter nitrogen than is ultimately needed in the system. The benefits actually delivered depend
not only on an ecosystem’s capacity to provide services, but also on demand for these services,
which is, in turn, driven by biophysical setting, population size, cultural preferences, and the
perceived value of the service. Demand for an ES can change independently of capacity, and
vice versa. Thus, measurements of any one component of ES delivery cannot capture the full ES
dynamic from production to benefit (Fig. 1). Despite this, studies that measure only one or two
components of ES provision are common (Tallis et al., 2012).
Frameworks for conceptualizing and analyzing ES are rapidly evolving (Boyd and
Banzhaf, 2007; Wallace, 2007; Costanza, 2008; de Groot et al., 2010; Nedkov and Burkhard,
2012; van Oudenhoven et al., 2012), with little consensus on which framework or analytical
products are most useful for environmental decision-makers. Some recent conceptual
frameworks distinguish components of ES delivery (e.g. demand; Tallis et al., 2012), but
definitions of components and relations among them differ widely across authors. For example,
capacity has also been referred to as potential supply (Burkhard et al., 2012), ecosystem potential
(van Oudenhoven et al., 2012), stocks of nature, and ES per se (Norgaard, 2009; Layke, 2009),
yet the basic concept behind each term is the same. In contrast, there seems to be weaker
consensus on how service flows, the benefits actually delivered to people, are measured or
defined (Fig. 1). Terminology often differs along an ecology-economics continuum, ranging
from economic concepts such as benefits (Wallace, 2007; Balmford et al., 2008) or supply (Hein
et al., 2006) to ecological concepts like performance indicators (de Groot et al., 2010) or flow
(Beier et al., 2009; Layke 2009). Moreover, some studies focus on the mechanics of ES delivery
(Bagstad et al., 2012) while others emphasize the ecosystem properties and processes that
influence the service production (de Groot et al., 2010; van Oudenhoven et al., 2012). While the
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breadth of approaches has surely furthered the exploration of services and has likely enhanced
our ability to evaluate services, the disparate terminology and subtle differences among
frameworks can inhibit managers and decision-makers from choosing an approach appropriate to
their needs. To enhance our ability to quantify, map, and ultimately make ES information more
accessible to decision-makers, we must acknowledge the inherent differences among ES types
(Table 1), the dynamic process by which ES are produced (Fig. 1), and how ES benefit people
(Carpenter et al., 2009; Bagstad et al., 2012; Chan et al., 2012). The key is finding a flexible and
adaptive approach that still allows consistency while avoiding rigid, one-size-fits-all frameworks.
Ecosystem services are categorized in multiple ways, with different categories being
amenable to different analytical approaches and providing distinctive societal benefits (MA,
2005). However, incorporating differences among service categories in ES assessments while
acknowledging their interconnectedness has been difficult. Some researchers group ES based on
their contribution to human well-being: services that directly benefit people (e.g. water supply)
are considered final or end services while many regulating and supporting services that
contribute to provision of final services are considered to be intermediate services. Intermediate
services are often excluded from economic valuations to avoid double counting (Boyd and
Banzhaf, 2007; Fisher and Turner, 2008; Wallace, 2008), but, in some cases, changes in
intermediate service provision are central to the potential societal trade-offs associated with
environmental management decisions. Limiting ES assessments to final services precludes
considering environmental and economic trade-offs, often resulting in the undervaluation of
services across the board (Keeler et al., 2012). Improving ES assessments requires development
of methods for quantifying intermediate or regulating service capacity, demand, and flow in
biophysical terms (Layke, 2009; Chan et al., 2012; Keeler et al., 2012).
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To help advance a common language associated with ES assessments and further the
application of ES frameworks, we reviewed and synthesized the literature on basic components
of ES delivery. From this synthesis we promote a framework in which an ES delivery model
comprises four distinct components: capacity (i.e. the potential to provide a service), ecological
pressures (i.e. anthropogenic and natural stressors on ES provision), demand (i.e. the amount of
service required or desired by society), and flow (i.e. the actual production of a service
experienced by people). Second, we discuss how the interpretation and measurement of these
components of ES differ among provisioning, regulating, and cultural ES and how measures of
each can be used to evaluate sustainability. Third, we discuss a new approach to evaluate
capacity, ecological pressure, demand, and flow specifically for regulating services (RS), which
are often left out of ES assessments due to complexities associated with quantifying them. To
strengthen the methodology for assessing RS, we describe how to quantify RS flow using
estimates of ecological pressure and environmental quality.
2. Distinguishing service capacity, pressure, demand, and flow
Separately measuring the components of ES delivery adds clarity to ES analyses and can
enhance integration into environmental planning and development. By distinguishing among ES
capacity, demand, ecological pressures, and flow we can 1) assess the current and future
biophysical capacity of an area to produce ES, 2) evaluate the sustainability of ES use under
different scenarios of ES demand, pressure, and capacity, and 3) examine how ES demand and
ecological pressures influence biophysical capacity via feedback loops in which pressure may
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exceed ecological thresholds (Carpenter et al., 2009). By comparing measures of current and
future capacity, ecological pressures, demand, and flow planners can evaluate whether a) the
needs of people can be met by existing ecosystem properties and processes, b) technological
substitutes are needed to supplement service production, c) ES flows will be equitable, and d) the
flow of services is sustainable (i.e. doesn’t degrade ES capacity).
2.1. Service capacity
Service capacity is an ecosystem’s potential to deliver services based on biophysical
properties, social conditions, and ecological functions (Cairns, 1997; Chan et al., 2006; 2011;
Egoh et al., 2008; Daily et al., 2009; van Oudenhoven et al., 2012). ES capacity is site- and time-
specific, but not static; capacity responds to natural or anthropogenic changes over time and
space. Land use and human population changes have an acute effect on ES capacity as well as
ES demand, ecological pressures and ES flows (Fig. 2; also Burkhard et al., 2012; van
Oudenhoven et al., 2012). Capacity can be measured and mapped by integrating the natural and
anthropogenic factors that influence the ecological properties and functions that provide services
regardless of how many people use or benefit from the services in question (Table 1).
Provisioning service capacity is typically measured directly by ecosystem properties (e.g.,
volume of water supply). Although more difficult to measure, cultural service capacity depends
on a mix of biophysical (e.g. climate, topography, presence of key species) as well as
anthropogenic conditions (e.g. accessibility by humans, site management actions; Villamagna et
al., in review). Capacity of an ecosystem to provide regulating services is also challenging to
measure. Regulating service capacity tends to comprise several interconnected ecosystem
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processes that each rely on a suite of ecosystem properties (Fig. 3). Thus measuring regulating
service capacity requires extensive knowledge of ecological processes, understanding of
ecological and hydrologic processes, process-based models and their limitations (e.g. Revised
Soil Loss Equation), and/or extensive field data .
2.2. Ecological pressure
Ecological pressures are biophysical influences that interfere with an ecosystem’s ability
to provide the service. They do so by increasing the work (i.e. effort) needed to provide the
service or by reducing an ecosystem’s capacity to deliver service (MA, 2005; WRI, 2012).
Ecological work includes the processes that generate the service and are discussed further in
sections 2.4 and 4.2. Pressures make it more difficult for an ecosystem to meet societal demand
for that service (see section 2.3) and sustained or extreme pressures can alter the future capacity
of an ecosystem to deliver services (Carpenter et al., 2009). Pressures on ES can be natural, like
periodic weather fluctuations, or anthropogenic, like increases in impervious surfaces. The
source of the pressure can be related to overuse, like overfishing or crowding in recreation areas
(Fig. 1), or it can be a by-product of ES trade-offs, like aquatic nutrient inputs from agricultural
production. The World Resources Institute (WRI) manages an online database on ES indicators
including direct and indirect drivers and service pressures (WRI, 2012). Our use of “pressure”
varies slightly from that of the WRI in that we include direct drivers as service pressures if they
are measured in the same units as the flow of the service (e.g. nutrient inputs conveyed through
fertilizers and changes in land cover).
2.3. Service demand
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Demand for ES, the amount of service desired by society, has been measured by a variety
of indicators (Table 1). Human population density combined with average consumption rates is a
common indicator (Burkhard et al., 2012; Nedkov and Burkhard, 2012), especially for services
that directly impact human well-being, such as water supply or crop production. For many
provisioning services, demand is concisely represented by market prices. For experience-based
cultural services, the number of people wanting to experience the ES (e.g. visitors to a park) can
indicate demand. Since RS produce or maintain desirable environmental conditions, societal
demand should be expressed as the amount of regulation needed to meet a desired end condition
(e.g. the percentage reduction needed to meet numeric criteria for a pollutant). Estimating RS
demand is inherently challenging because it requires information about desired end conditions as
well as the ecological pressures or inputs needing regulation. To date, few assessments have
quantified RS demand biophysically. Instead, RS demand has been measured in terms of human
population (Burkhard et al., 2012; Nedkov and Burkhard, 2012), which is weakly related to the
amount of regulation actually occurring.
For all ES, demand -- an outcome of socio-cultural preferences -- can exceed capacity,
but capacity ultimately sets the limit on long-term service provision. Burkhard et al. (2012) and
Nedkov and Burkhard (2012) found that demand for services as measured by population density
of beneficiaries largely exceeds service capacity in urban areas, whereas the opposite is true in
less-populated rural areas. While demand for provisioning and cultural services can be met by
moving resources or people, demand for RS must often be met locally. Sometimes this demand
can be met by a technological substitute, but often the substitute meets a single demand rather
than the suite of demands that might be met by natural systems. For example, ecosystems with
high capacity to purify water provide clean drinking water, healthy aquatic habitats, and sources
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of aquatic recreation (Keeler et al., 2012), but water treatment plants may only address the
drinking water demand.
2.4. Service flow
We consider service flow to be the service actually received by people, which can be
measured directly as the amount of a service delivered, or indirectly as the number of
beneficiaries served. Total service flow can be quantified as the service delivery per beneficiary
multiplied by the number of beneficiaries (Table 1). Like other components of the ES delivery
process, we suggest incorporating differences among ES types into measurements of service
flow (Table 1). For provisioning services, the conventional metric of service flow is the
equivalent of the end good (e.g. timber production). Cultural services are similar to provisioning
in that the flow of cultural service is conventionally measured in terms of the duration and
quality of the experience with nature. Although inherently challenging to analyze because they
are individualistic, difficult to aggregate, and sometimes influenced by social or moral factors
(Chan et al., 2012), many cultural service flows are estimated using market and non-market
techniques. In contrast, regulating services lack a clear end product that is tractable or
commonly represented in markets. Instead, environmental quality has been adopted as a
convenient metric of service flow and ecosystem state (Dale and Polasky, 2007; Martinez et al.,
2009). However, simply measuring environmental quality does not necessarily convey the
amount of ecological work or regulation that has occurred because the amount of ecological
pressure on the ecosystem itself and the capacity to regulate also play a role. Environmental
quality is the result of multiple services, regulating and provisioning, working against ecological
pressures. Instead, we propose that the flow of a regulating service be measured in terms of the
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ecological work required to mitigate pressures and deliver the service demanded. We further
discuss ecological work in measures of regulating service flow in section 4.2.
While service capacity is site-specific, service flow is not limited to the site of
production. Consider downstream benefits of clean water from upstream soil or nutrient
retention. Where benefits can be experienced, given natural and anthropogenic pathways, is the
benefit zone (Bagstad et al., 2012) and the people within the benefit zone are potential
beneficiaries (Hein et al., 2006; Boyd and Banzhaf, 2007; Johnston and Russell, 2011; Martin-
López et al., 2011). The proximity and capacity of ES sources and pathways defines the potential
benefit zone, but natural and anthropogenic connectivity across landscapes influences
spatiotemporal patterns of ES flow (Fig. 4; also Fisher et al., 2008; Bagstad et al., 2012).
Moreover, some services are passively delivered to beneficiaries (e.g. clean air), while others
require additional capital inputs on the part of the beneficiary (e.g. financial or physical capacity
to access recreation services). Sometimes long-distance ES flows are fundamentally
asymmetrical, creating social inequity in terms of the human well-being derived from ES
management (Carpenter et al., 2009; Tallis et al., 2012).
The terms and methods used to describe ES flow are especially wide-ranging relative to
other components of ES delivery (Fig. 1). Although service flow represents the actual delivery of
services and capacity represents the potential production of services, these concepts are
sometimes used interchangeably (Layke, 2009), which can lead to misinterpretations of ES
condition that affect decision-making. Service flow is an important measure of current ES
delivery, whereas capacity provides a measure of the potential of the system. Flow and capacity,
and their measures, must be consistently distinguished in order to accurately evaluate changes in
service delivery over time and to identify areas of potential ES production in the future.
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Recognizing the differences between ES capacity and ES flow is an important step towards
better understanding how changes in policy and management can affect ES values accruing to
beneficiaries.
3. Service delivery and sustainability
The benefit of the conceptual framework we have laid out here is that distinguishing
among measures of ES capacity, demand, pressure, and flow enables assessment of ecological
sustainability and identification of key trade-offs (McDonald, 2009). Given that areas of high ES
capacity and flow are often spatially mis-matched and that ES demand is influenced by many
factors extraneous to service production (e.g. technological substitutes for ES, cultural values,
and behavioral norms), quantifying ES components separately is an important step towards
enhancing the ability of ES assessments to inform environmental decision-making. Spatially
explicit ES budgets, the comparison of ES demand and capacity, can identify areas where
technological substitutes or additional capital inputs will be needed to meet demand, and,
likewise, areas where greater development and ES flow can be supported. ES flow is sustainable
when demand is met by flow without decreasing capacity for future provision of that service
(Fig. 1). ES flow is not sustainable when demand cannot be met by current capacity or when
meeting demand causes undesirable declines in other services or in the future provision of the
same service. For example, the flow of water purification services from a watershed would be
considered unsustainable if the quality of the water produced consistently failed to meet stated
criteria or the only way to meet those criteria was to significantly reduce food production.
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Trade-off analyses (Rodríguez et al., 2006; Daily et al., 2009; Raudsepp-Hearne et al.,
2010) can help assess landscape-level ES sustainability. Prolonged periods of excess ecological
pressure or overuse may shift ecosystem functions in ways that permanently alter ES capacity
and delivery (Scheffer and Carpenter, 2003; MA, 2005). For example, protracted over-
exploitation of tree, fish, and game populations decreases stocks and regenerative capacity of
provisioning services (Hilborn et al., 1995; Larkin, 2000). When ES demand exceeds ecosystem
capacity to provide services, society generally has three choices to avoid environmental damage
and decreases in human well-being. First, people can enhance the system’s natural capacity to
provide the services demanded, for example by applying fertilizers to increase food production.
Second, people can recognize that supply is limited and reduce their demand appropriately.
Third, people can invest in technology to help avoid the outcomes of diminished services. For
example, we build dams, levees, and seawalls to reduce flood damage when landscapes cannot
adequately modulate flood magnitude and frequency. While some technological solutions
address a single service (e.g. water treatment plant) and fail to restore all potential benefits from
a non-degraded system (e.g. habitat provision), others create novel ecosystems that enhance
multiple services (e.g. a reservoir provides water supply, flood regulation, and recreation). In
contrast, management choices can negatively impact the capacity of other services (Bennett et
al., 2009) and a change in the flow of one service can greatly influence the ecological pressures
on another service (Rodríguez et al., 2006; Barbier, 2009). Given the complex interactions
among services, understanding ES trade-offs based on analyses that quantify capacity, demand,
pressure, and flow are potentially valuable contributions of ES science to environmental
decision-making.
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4. Moving forward with regulating services
We suggest that distinguishing among the four components of ES delivery will provide
planners with better information for decision-making. To successfully integrate this multi-
component framework into ES assessments, we must enhance our understanding of how RS
function and develop stronger methods for quantifying the demand for and flow of RS.
Regulating services are integral to the delivery of provisioning and cultural services, yet RS are
declining globally (MA, 2005; Carpenter et al., 2009). Regulating services are process-driven
and, unfortunately, the data needed to directly measure their condition are often unavailable at
scales large enough to support policy-making (Layke, 2009). Below, we review how RS differ
from other service types and how this impacts the way we should quantify the components of
RS.
4.1. Regulating services are inherently different
Regulating services are distinct in that they often exert significant influence on the
capacity to provide other services (de Groot et al., 2002; Boyd and Banzhaf ,2007), but direct
impacts of RS on human well-being can be difficult to measure (Keeler et al., 2012). Even
though RS provide important benefits for humans (e.g. water and air purification, drought or
flood control, and regulation of disease), they tend to change slowly and are thus less amenable
to typical scientific study. Few comprehensive and reliable ecological indicators are monitored
for RS (Layke, 2009), which makes their value difficult to express in biophysical or monetary
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units. In addition, without market prices as indicators of their supply and demand, changes in
capacity may go largely unnoticed (Cairns, 1997). Often, the value of RS is not apparent until the
declines cause problems for other, more commonly measured services (e.g. floods or droughts
affecting agricultural production). Together, the lack of economic and biophysical evaluations
leads to the general undervaluation of RS and their absence in many planning decisions.
4.2. Measuring demand for and flow of regulating services
Regulating services help maintain environmental quality within socially desirable
ranges. The amount of RS delivered will vary among ecosystems depending on ecological and
social pressures and capacities. Based on our four component framework, measuring regulating
service flow requires information about both ecological pressures on the ecosystem providing the
service and societal demand for the service itself. However, environmental quality (e.g. water
quality) is often used as an indicator of regulating service flow (Dale and Polasky, 2007;
Martinez et al., 2009; Shibu, 2009). Key strengths of using environmental quality as a proxy for
some RS is that it is readily measured, meaningful to society, and changes in quality can be
expressed in economic terms through market and non-market valuation (Farber et al., 2006).
However, environmental quality is not equal to the capacity, pressure, demand, or flow of the
service; instead it depends on the service capacity, relative pressure on the ecosystem and service
processes, and for some, the flow of other services (e.g. nitrogen regulation is affected by
stormwater regulation).
In real landscapes, high environmental quality may be the result of high capacity to
regulate anthropogenic stress or weak ecological pressures. High-capacity systems are capable of
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greater ecological work to regulate pressures, resulting in slower or less change in environmental
quality (i.e. more regulation). A system with no (or very low) capacity to regulate (Fig. 5A)
experiences quick decline in environmental quality (y axis) with increases in ecological pressure
(x axis), while systems with higher capacity (Fig. 4B) can maintain acceptable environmental
quality under great ecological pressure. Similarly, systems with identical capacity can differ in
environmental quality due to differences in ecological pressures. Consider two watersheds in
which water quality is equal and meets societal standards (i.e. demand), but differ in contaminant
loading. One receives heavy nutrient loading as it flows through a mixed crop-forest landscape
with fertilizer inputs while the other flows through a similar landscape mosaic without fertilizer.
Although downstream nutrient concentrations are similar, ecological pressures differ markedly
and the ecological work occurring is greater in the fertilized watershed. Simply using ambient
water quality as a surrogate for RS flow cannot distinguish these two systems since it not only
ignores the relationship between ES capacity and pressure, but does not differentiate among the
multiple processes that affect water quality (e.g. filtration, sedimentation, volatilization, plant
uptake; Fig.3).
Instead of using environmental quality as an indicator of RS flow, we propose estimating
the ecological work performed as the difference between ecological pressures and measured
environmental quality. For example, the flow of sediment filtration services can be estimated by
calculating the difference between ambient sediment concentrations (e.g. total suspended solids)
and cumulative sediment loading throughout the watershed. Likewise, the flow of carbon
sequestration should be measured as the amount of carbon taken up and stored in vegetation,
rather than the amount of atmospheric carbon. Ecological work provides a measure of RS flow
that cannot be deduced from environmental quality measures alone. Ecological pressures, like
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sediment loading, can be quantified in several ways, including direct field monitoring or
estimated by widely accepted models, like the Revised Universal Soil Loss Equation (RUSLE)
or Soil and Water Assessment Tool (Sahu and Gu, 2009). Since absolute values may not exist for
all ecological pressures or for environmental quality in all areas, relative measures can be used.
Where neither relative measures nor appropriate models exist, expert judgment is an alternative
(MA, 2005; Burkhard et al., 2012; Nedkov and Burkhard, 2012). The analytical goal is to
incorporate spatiotemporal variability in ecological pressures to better evaluate RS flow. By
evaluating ecological pressures in conjunction with environmental quality, we get a more reliable
estimate of RS flow which can be compared to estimates of capacity to assess the state of the
ecosystem, the condition of the service, and sustainability of current land practices.
Our approach to estimating RS flow is designed to provide information to avoid
ecological degradation, but may also be helpful in developing mitigation strategies to reduce
existing degradation. Once areas of high ecological pressure and low capacity are known,
degradation can be avoided by reducing pressures, increasing capacity (e.g. via restoration or
best management practices), or enhancing the capacity of other services that influence pressures.
Identifying which ecosystem properties and processes contribute to RS capacity and which land
use practices influence ecological pressure (Fig. 2) can help managers develop strategies to plan
for or mitigate changes in environmental quality.
5. Conclusions
Our approach to assessing ES, using separate measurements of ES capacity, pressure,
demand, and flow, is useful and innovative in that it quantifies the components of ES delivery
rather than merely measuring final services or environmental quality. By so doing, we can more
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accurately characterize service delivery, sustainability, and ES trade-offs across space and
through time. Using information about all four aspects of ES, planners can more effectively
evaluate whether the needs of people can be met sustainably (i.e. without degradation) by
existing capacity or if alternative measures are needed (e.g. restoration or technological
substitutes). This multi-component ES approach also enables scientists to assess regulating
services more accurately by measuring RS flow as the regulation of ecological pressures, rather
than measures of environmental quality. Measuring the actual flow of services provides a metric
for assessing ES equity, while capacity measures inform decisions about future development and
management. Collectively, our multi-component framework offers a more comprehensive
assessment of ES delivery, sustainability, and the trade-offs associated with land use. Our
approach also accounts for temporal variability in all components of ES provision, especially
ecological pressures and societal demand, which are likely to change through time.
To facilitate widespread use of ES knowledge in environmental management and
conservation planning, we need a more flexible, coherent, and informative framework that
accounts for spatiotemporal differences in how ES are produced and delivered (de Groot et al.,
2010; Chan et al., 2012). This framework should distinguish between potential service
production and the flow of services and be applicable across a wide range of ecosystems and
services (de Groot et al., 2010; Tallis et al., 2012). Our approach for analyzing ES represents
significant steps toward meeting these needs as this ES framework can be applied at virtually any
spatial resolution or extent for which ES components are measured separately. Furthermore, the
framework can be easily incorporated into scenario analyses (MA, 2005; Troy and Wilson, 2006)
to produce more objective and accurate assessments of service capacity, ecological pressure,
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expected demand, and service flow which can better guide land management decisions (van
Oudenhoven et al., 2012).
Acknowledgments
This work was funded by the U.S. Geological Survey’s National Aquatic Gap Analysis
Program. We thank D. Beard, C. Beier, E. Frimpong, K. Limburg, B. Mogollon and anonymous
reviewers for their valuable input and feedback throughout the development of this and related
studies. The Virginia Cooperative Fish and Wildlife Research Unit is jointly sponsored by the
U.S. Geological Survey, Virginia Polytechnic Institute and State University, Virginia
Department of Game and Inland Fisheries, and Wildlife Management Institute. Use of trade
names or commercial products does not imply endorsement by the U.S. government.
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Table 1
Components of ES
Delivery
ECOSYSTEM SERVICE CATEGORIES
Provisioning Regulating Cultural
ECOSYSTEM
SERVICE CAPACITY:
An ecosystem’s potential
to deliver services based
on biophysical and social
properties and functions1
Biophysical
capacity; feature-
based
(e.g. modeled water
supply)
Biophysical
capacity;
process-based
(e.g. modeled
carbon
sequestration)
Biophysical and social
capacity; feature- and
process-based
(e.g. model potential
to provide experience)
ECOLOGICAL
PRESSURES:
Anthropogenic and
natural stressors that
affect capacity or flow of
benefits; often attributed
to overuse or feedback
from land management
decision to enhance other
service capacities2
Events that reduce
stock and/or
regenerative
capacity (e.g.
overharvest; water
impoundments)
Environmental
disturbances that
increase the amount
of ecological work
required to meet
societal demands
(e.g. pollution,
impervious
surfaces)
Events that reduce
stock, regenerative, or
assimilative capacity
of a system;
commonly related to
overuse
(e.g. soil compaction,
erosion)
ECOSYSTEM
SERVICE DEMAND:
The amount of a service
required or desired by
society3
Amount of service
desired per unit
space and time
multiplied by the
number of potential
Amount of
regulation needed
to meet pre-
determined
Desired total use (if
rival service) or
individual use (if non-
rival)
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users (rival service)
(e.g. liters of water
per person)
condition
(e.g. % nitrogen
reduction; TMDL)
(e.g. total visitor-days
from year prior;
individual visitation
rates)
ECOSYSTEM
SERVICE FLOW: The
actual production or use
of the service;
incorporates biophysical
and beneficiary
components4
Quantity harvested,
consumed, or used;
number of people
served; number of
industries served
Ecological work =
ecological pressures
minus
environmental
quality (same units)
(e.g. nitrogen
inputs-in-stream
load)
Amount of service
used measured in
units of time and/or
space
(e.g. total visitor-days
from current year;
individual visitation
rates)
1Cairns (1997); Chan et al. (2006); (2011); Egoh et al. (2008); Daily et al. (2009); van
Oudenhoven et al. (2012). 2Beier et al. (2008); Rounsevell et al. (2010); van Oudenhoven et al.
(2012). 3McDonald (2009); Nedkov and Burkhard( 2012). 4Beier et al. (2008); Layke (2009); de
Groot et al. (2010); Oudenhoven et al. (2012).
28
Table captions
Table 1: Ecosystem service delivery process comprises four distinct components which differ
among three ecosystem service categories. A general definition and examples are provided for
each category-component combination.
Figure captions.
Fig. 1: The main components of the ecosystem service delivery process (boxes) are
interconnected such that a change in one affects the others (arrows). A wide array of terms has
been used interchangeably throughout the literature. For each main component (box), we cite
authors who have adopted that term and provide alternative terminology cited in the literature.
Ecological pressures (pink box) have a direct effect on the capacity of an ecosystem to provide a
service and can affect the flow of the services (black box). Likewise, societal demand (red box)
can influence ecological pressures and the flow of services from ecosystems to beneficiaries
(purple box) and the needs and preferences of beneficiaries influence societal demand.
Fig. 2: Conceptual models illustrating the effects of land use (middle) and human population
(right) changes on regulating service (RS) capacity, ecological pressures, societal demand for
regulating services, and the flow of services in a watershed in which upstream areas are largely
forested e.g. 80-year rotation timber production) and downstream areas are predominantly
agricultural and rural-suburban development left). The middle panel illustrates how a clear-cut,
for coal extraction or a housing development, in the upper forested area would decrease the
landscape’s water retention capacity, which would increase runoff and ecological pressure on
flood regulation downstream. Similarly, the loss of forested cover would likely decrease the
sediment retention capacity upstream, thereby increasing ecological pressure on sediment
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regulation in the lower basin. In this case, service flow increases because of the additional work
the ecosystem must perform to maintain desired environmental quality. Service flow can also
increase because of additional beneficiaries. The right panel illustrates how an increase in human
population density downstream would increase the societal demand for the regulating service.
Increases in ecological pressure or societal demand will increase service flow, given that the
system has sufficient capacity to produce the service.
Fig. 3: Conceptual model illustrating water quality regulation. the movement of water across the
landscape (surface and subsurface), and the major components of the ecosystem service delivery
process, including capacity (green boxes), ecological pressures (pink ovals), demand (red
arrows), and service flow (black arrows). Beneficiaries (purple ovals) are shown as the source of
demand and the recipients of regulating service flow. As water is introduced to the ecosystem, by
means of precipitation or upland flow, a series of processes can act to regulate water quality.
High capacity of horizontal and vertical retention reduces the ecological pressures on surface
filtration and deposition.
Fig. 4: The flow of ecosystem services (ES) can vary greatly depending on area of service
production, its natural flow paths, as well as anthropogenic flow corridors. For many freshwater-
related services the flow path is naturally hydrologic where the capacity to produce a service
upstream affects the flow of benefits downstream top). Alternatively, the benefit zone can be
extended by anthropogenic corridors like roads, canals, or exportation bottom).
Fig. 5: Differences in service delivery and the effects of ecological pressure on environmental
quality and ecological work within ecosystems with little to no capacity A) compared to that of a
system with high regulating capacity B). Environmental quality is a function of regulating
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capacity and ecological pressure. In systems with little to no capacity A), environmental quality
is quickly degraded in response to increasing ecological pressure. Systems with higher capacity
can maintain better environmental quality under greater ecological pressure B). Ecological
thresholds are determined by the ecosystem’s capacity to provide a service. Once this threshold
of ecological pressure is exceeded, environmental quality will degrade. The shaded polygon B)
illustrates the amount of ecological work performed i.e. regulating service flow), which
represents the difference between environmental quality and ecological pressure.
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