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Earth Science Matters is produced by the U.S. Geological Survey Land Change Science Program. All content is copyright free, and can be reprinted without permission. Comments, feedback, and suggestions for future stories are welcome. If you would like to subscribe please enter your email address and click the “Subscribe” button on the Program Newsletter page.
U.S. Department of the Interior U.S. Geological Survey
Volume 9, Fall 2019
News from the USGS Land Change Science Program
Earth Science Matters
Changes in the way we use and manage land, as well as changes in
climate, affect our natural resources, infrastructure, and communities in
complicated ways. To help managers and policy makers design
sustainable management strategies, scientists are studying the effect
these changes can have on habitats, ecosystems, and the processes that
maintain them. This research aims to improve our understanding of
environmental processes and our ability to anticipate the impacts of a
range of future changes. The USGS Land Change Science Program
sponsors research that integrates long-standing expertise in geology,
ecology, hydrology, and geography to provide a scientific basis for
sustainable management strategies being developed by the Department
of the Interior and other stakeholders.
Reconstructing extreme floods in eastern North America using sedimentary records
Photo Courtesy of Jamie Hayward, California State
University—Fullerton.
USGS and Stakeholder Engagement in the Gulf of Mexico
LCS Research Activities: Arctic Research Cruise
To manage forest response to drought, pay attention to “the little things that run the world”
Geologic records of a warmer Arctic in the past
Improved Urban Maps for the United States
Implications for mangrove range expansion with changing climate
Earth Science Matters is produced by the U.S. Geological Survey Land Change Science Program. All content is copyright free, and can be reprinted without permission. Comments, feedback, and suggestions for future stories are welcome. If you would like to subscribe please enter your email address and click the “Subscribe” button on the Program Newsletter page.
U.S. Department of the Interior U.S. Geological Survey
Volume 9, Fall 2019
News from the USGS Land Change Science Program
Earth Science Matters
This issue of Earth Science Matters highlights recent collaborations with stakeholders and newly published research
products that contribute to an improved understanding of how changing land use, climate, and environment affect
communities, ecosystems, and the services they provide. Topics covered include:
• USGS collaborations with
Gulf Coast stakeholders to
support management of
coastal wetlands
• Documenting extreme flood
history in the Chesapeake Bay
watershed and the influence of
climate patterns on storms and
floods
• Geologic records of Arctic
temperature and hydrology
during past intervals of
elevated carbon dioxide in the
atmosphere
• Combined role of drought and
insects on tree mortality
• Improving urban maps by
removing rural roads from
land cover datasets
• Impacts of soil type, temperature, and local factors on mangrove distributions and health
• USGS participation in a research cruise to study glacial history of the Ryder Glacier in Greenland
Data generated by these studies provide real-world evidence needed to test and develop models that project changes
under different land use and climate scenarios.
Earth Science Matters includes a sampling of the multidisciplinary research conducted by the Land Change Science
Program to provide data and improve understanding on the rates, patterns, and consequences of changing environment,
climate, and land use. We welcome comments and feedback to shape future issues. If you would like to subscribe to
future issues, please click the “Subscribe” button on the Program Newsletter page.
Debra Willard
Coordinator, Land Change Science Program
Photo Courtesy of David Clow, USGS
Earth Science Matters is produced by the U.S. Geological Survey Land Change Science Program. All content is copyright free, and can be reprinted without permission. Comments, feedback, and suggestions for future stories are welcome. If you would like to subscribe please enter your email address and click the “Subscribe” button on the Program Newsletter page.
U.S. Department of the Interior U.S. Geological Survey
Volume 9, Fall 2019
News from the USGS Land Change Science Program
Earth Science Matters
The U.S. coast of the Gulf of Mexico
stretches about 1,631 miles from southern
Florida through Alabama, Mississippi, and
Louisiana, ending at the U.S.-Mexico
border in Texas. Along this coastline are
numerous types of coastal wetlands that
provide many societal benefits. Coastal
wetlands comprise grassy salt marshes,
mangrove forests, freshwater forested
swamps, freshwater marshes, and tidal
flats. In addition to supporting fish and
wildlife habitat, these wetlands improve
water quality by filtering out excess
nutrients and contaminants, sequester
carbon and release oxygen, stabilize the
shoreline to control erosion, provide
recreation and tourism opportunities, and
protect coastal communities from
storms. USGS Land Change Science
Program (LCS) researchers are studying
these important ecosystems and
communicating with local natural
resource managers to better inform their
management.
Coastal wetlands have immense economic value, with estimates averaging about $194,000 per hectare per year on a
global scale (2007 US$ price level) (Mehvar et al., 2018). For example, almost all the fish and shellfish caught by the
fishing industry depend on estuaries and wetlands at some point in their life cycle, and the money brought in annually by
the fishing industry in the Gulf region reaches hundreds of millions of dollars. Loss of healthy coastal wetland habitats
can have severe impacts not only on fish populations, but on the fishing industry and regional economy as well. Coastal
wetlands also incur economic value from their recreational use (fishing, kayaking, hiking, etc.), provisioning of raw
materials (food, fiber, wood), and protective nature (prevent erosion, filter pollution, hold excess rain to help control
flooding).
However, due to their position at the land-sea interface, coastal wetlands are highly dynamic, variable, and vulnerable to
major change. Coastal wetlands face pressure directly from natural coastal hazards such as flooding and erosion but also
are indirectly threatened from human population growth and economic development. Coastal areas make up 4% of the
land area on earth but are home to about a third of the global population, and the population density along the coasts
Earth Science Matters is produced by the U.S. Geological Survey Land Change Science Program. All content is copyright free, and can be reprinted without permission. Comments, feedback, and suggestions for future stories are welcome. If you would like to subscribe please enter your email address and click the “Subscribe” button on the Program Newsletter page.
U.S. Department of the Interior U.S. Geological Survey
Volume 9, Fall 2019
News from the USGS Land Change Science Program
Earth Science Matters
continues to grow each year spurring increased land conversion and development (Mehvar et al., 2018). Additionally, as
the planet’s climate changes, the natural hazard events that coastal wetlands are susceptible to, including changes in
precipitation and warming temperatures, are expected to increase in probability and severity.
The Gulf Coast is home to many parks, refuges, and other public lands. Managers at those locations have responsibility
for managing their lands to preserve natural resources and the services they provide. USGS scientists are collaborating
with managers at Apalachicola National Estuarine Research Reserve (ANERR), Florida Forest Service (FFS), Florida
Fish and Wildlife Research Institute (FWRI), and Mission Aransas National Estuarine Research Reserve (Mission-
Aransas NERR) (among others) with the aim of providing unbiased, robust science to guide and support their
environmental management decisions.
These resource managers are tasked
with monitoring species, providing
public use and access to natural lands,
managing habitat and restoration
efforts, protecting and managing natural
resources to ensure their availability for
future generations, collecting and
analyzing scientific data to inform
climate change adaptation, promoting
understanding of coastal ecosystems to
diverse audiences, and promoting
public appreciation and support for
stewardship of coastal resources.
Current State of Knowledge
Wetland vulnerability assessments have been used to identify coastal areas that are most susceptible to environmental
change or stress. Previous coastal wetland vulnerability assessments have generally focused solely on sea-level rise
without considering the effects of other facets of climate change. Across the globe and in all ecosystems, macroclimatic
drivers (e.g., temperature and rainfall regimes) greatly influence ecosystem structure and function. In some coastal
wetlands, research suggests that changing macroclimatic conditions could result in the replacement of foundation plant
species (species that have a strong role in structuring an ecosystem, such as mangrove trees, salt marsh graminoids, and
succulents in coastal wetlands).
Foundation plant species are able to withstand and moderate the physically stressful tidal conditions, and they provide
primary, tolerable habitat for a wealth of other species. They supply important ecosystem goods and services, such as
water filtration, and wave energy absorption, and increase the resilience of the ecosystem under a range of environmental
stressors. USGS scientists are working to improve our understanding of the impact of macroclimate drivers and
ecosystem dynamics in coastal ecosystems by documenting how changes in temperature and rainfall regimes affect
coastal wetland systems.
Earth Science Matters is produced by the U.S. Geological Survey Land Change Science Program. All content is copyright free, and can be reprinted without permission. Comments, feedback, and suggestions for future stories are welcome. If you would like to subscribe please enter your email address and click the “Subscribe” button on the Program Newsletter page.
U.S. Department of the Interior U.S. Geological Survey
Volume 9, Fall 2019
News from the USGS Land Change Science Program
Earth Science Matters
USGS Research Benefitting Gulf Coast
Stakeholders
We recently began surveying stakeholders for USGS
LCS research to evaluate their science needs and
potential synergies between them and USGS research
efforts in order to maximize the relevance of our efforts
to stakeholders in various federal, state, and local
agencies.
A common goal of the stakeholders is development of
adaptation plans for wildlife and ecosystems that
promote long-term protection and management of
valuable coastal resources given an uncertain future.
Creating these adaptation plans is an important step in
preparing and protecting local communities for any
effects of change on the natural resources that they
depend upon. USGS research on the impacts of
macroclimatic changes on coastal foundation species
Earth Science Matters is produced by the U.S. Geological Survey Land Change Science Program. All content is copyright free, and can be reprinted without permission. Comments, feedback, and suggestions for future stories are welcome. If you would like to subscribe please enter your email address and click the “Subscribe” button on the Program Newsletter page.
U.S. Department of the Interior U.S. Geological Survey
Volume 9, Fall 2019
News from the USGS Land Change Science Program
Earth Science Matters
is producing maps and projections of vegetation response
to changing temperature and rainfall regimes. These
provide important evidence that support management
planning by resource managers in coastal wetlands.
Of particular interest to Gulf Coast stakeholders is USGS
monitoring and mapping of salt marsh and mangrove
extent under various past and future conditions. Maps of
potential mangrove range expansion into salt marshes
under different climate change scenarios allow
stakeholders to identify priority conservation areas and
create targeted monitoring programs. Likewise, maps of
marsh migration under different growth and
development scenarios allow stakeholders to weigh
costs and benefits of different management strategies.
Correlation of current mangrove forest extent maps with
state forest inventory characteristics provides a way for
state forest managers to better track and predict the future of mangrove ecosystems. Developing mangrove damage
assessments after hurricanes also helps managers track the natural resources, they are responsible for and to identify
potential areas for restoration projects.
The network of collaborating scientists and land managers from the USGS and agencies throughout the Southeast and
Gulf Coast leverages their collective expertise to examine how changing land management and environmental factors
affect coastal ecosystems in a comprehensive way. Local stakeholders and resource managers noted that they are able to
spend more time focusing on the “bigger pictures” and regional trends in land management because USGS scientists are
supplying rigorous, hypothesis-driven research and science products. Further, they are using USGS research to create
targeted restoration projects and environmental resource monitoring programs in their locality.
These collaborations also are helping USGS researchers tailor their research to address pressing questions while
achieving a core mission of the agency: to provide reliable scientific information to describe and understand the Earth.
As a result, scientists and resource managers are more effectively communicating the urgency and importance of
environmental change issues in the region to the public, state and local governments, nonprofits, and universities they
serve.
We gratefully acknowledge the support of the resource managers and stakeholder institutions who helped in the creation
of this piece.
References Cited
Mehvar, S., Filatova, T., Dastgheib, A., De Ruyter van Steveninck, E., and Ranasinghe, R., 2018, Quantifying economic
value of coastal ecosystem services: a review: Journal of Marine Science and Engineering, v. 6, no. 1, doi: 10.3390/
jmse6010005. https://www.mdpi.com/2077-1312/6/1/5
Earth Science Matters is produced by the U.S. Geological Survey Land Change Science Program. All content is copyright free, and can be reprinted without permission. Comments, feedback, and suggestions for future stories are welcome. If you would like to subscribe please enter your email address and click the “Subscribe” button on the Program Newsletter page.
U.S. Department of the Interior U.S. Geological Survey
Volume 9, Fall 2019
News from the USGS Land Change Science Program
Earth Science Matters
Historically unprecedented changes in Arctic weather, sea ice, glaciers, and temperature have led to concerns about
coastal erosion, ecosystem changes, and sea-level rise. Climate changes in the Arctic are “amplified” in that the
cryosphere (glaciers, ice sheets, sea ice), experiences changes that are larger in magnitude than those in lower latitudes.
Furthermore, changes in the Arctic affect the rest of the earth. Decreasing summer sea-ice cover in the Arctic Ocean
affects weather patterns in heavily populated mid-latitude regions. Melting of Arctic glaciers and of parts of the
Greenland Ice Sheet is increasingly recognized as a major contributor to present and future global sea-level rise.
Additionally, the resulting increase in fresh water influx to the oceans from this melt has the potential to alter patterns of
ocean circulation that affect temperature regimes throughout the globe.
The USGS Land Change Science Program (along with other programs within the bureau) conducts Arctic research to
better understand the drivers and impacts of change on glaciers, sea ice, permafrost, and hydrology. One of these
research projects, Land-Sea Linkages in the Arctic, is investigating the climatic history of the Arctic Ocean and its
adjacent seas and land areas using marine sediment cores collected throughout the region. These cores capture sediments
deposited up to 500,000 years ago and allow scientists to reconstruct the distribution of sea ice over time scales ranging
from the past centuries to millennia and even longer time scales.
Recently, two members of
the project, Thomas M.
Cronin and Laura Gemery,
participated in the Ryder
2019 Expedition of the
Swedish icebreaker Oden
(Figure 1) to northern
Greenland to collect
sediment cores in a
previously unstudied part of
the Arctic. The Expedition
conducted multidisciplinary
research on glacial history of
the remote Ryder Glacier,
which extends into the ocean
from the northern portion of
the Greenland Ice Sheet.
Research focused on the
relationship between the
Greenland Ice Sheet, Ryder
Glacier, and the ocean during
climate changes of the
Earth Science Matters is produced by the U.S. Geological Survey Land Change Science Program. All content is copyright free, and can be reprinted without permission. Comments, feedback, and suggestions for future stories are welcome. If you would like to subscribe please enter your email address and click the “Subscribe” button on the Program Newsletter page.
U.S. Department of the Interior U.S. Geological Survey
Volume 9, Fall 2019
News from the USGS Land Change Science Program
Earth Science Matters
Holocene, which covers the last 10,000 years. Understanding Holocene cryosphere-ocean history is critical as it provides
baseline information on pre-Anthropogenic natural variability and sensitivity of the ice sheet to early Holocene warming
and its contribution to sea-level changes.
Ryder 2019 took place from August 5 to September 12, 2019 and was led by co-chief scientists Dr. Martin Jakobsson of
Stockholm University and Dr. Larry Mayer, Director of the Center for Coastal and Ocean Mapping, University of New
Hampshire. The expedition explored remote regions of northwest Greenland including Ryder Glacier, which terminates
in the Sherard-Osborn Fjord, the Nares Strait, the Lincoln Sea, and the Petermann Glacier and Fjord (Figure 2). The
international team of scientists on the expedition conducted multidisciplinary studies in the fields of atmospheric
chemistry and physics, biology, climatology, ecology, genomics, glaciology, oceanography, marine geology, geophysics
and geochemistry.
One primary goal of
USGS scientists and their
Swedish collaborators
while onboard was to
investigate the dynamics
and history of the marine
cryosphere, which
includes glaciers
extending into fjords
from the Greenland Ice
Sheet and Arctic Ocean
sea ice. Greenland ice
tongues (floating ice
shelves) extend from
glaciers on the land into
the ocean (Figure 3). The
stability of these features
is influenced by both air
temperatures, which
affect melt rates on the
glacier surface, and
ocean temperatures,
which affect the bottom,
submarine portion of the
glacier. The potential instability of ice tongues, glaciers, and ice sheets under a warming climate is of concern because of
the potential contribution of melting ice to sea-level rise. Decreasing Arctic Ocean sea ice is also a major concern due to
its impacts on ecosystems, weather patterns, and ocean circulation.
Earth Science Matters is produced by the U.S. Geological Survey Land Change Science Program. All content is copyright free, and can be reprinted without permission. Comments, feedback, and suggestions for future stories are welcome. If you would like to subscribe please enter your email address and click the “Subscribe” button on the Program Newsletter page.
U.S. Department of the Interior U.S. Geological Survey
Volume 9, Fall 2019
News from the USGS Land Change Science Program
Earth Science Matters
Research on Oden by Drs. Martin
Jakobsson and Larry Mayer
involved geophysical mapping of
underwater glacial landforms,
which was used by USGS
scientists to select sites for coring
of seafloor sediments deposited
during the last 10,000 years.
These long-term
paleoceanographic records from
sediment cores are needed
because instrumental records
extend back only a few decades
and glaciers, sea ice, and climate
vary over longer time scales. By
combining geologic data from the
new cores with instrumental
records, USGS researchers and
colleagues aim to improve
understanding of how the Arctic
Ocean and adjacent land masses
have been influenced by a range
of natural and anthropogenic
factors.
While on the ship, USGS
scientists began analyzing
samples from new cores they
collected (Figure 4). They
measured the physical properties
of the sediments and analyzed
calcareous microfossils [foraminifera, ostracodes] that were buried in the sediments. These on-board analyses included
using the ecology of the microfossil species in the cores to develop a preliminary reconstruction of sea-ice history to
complement previous work elsewhere in the Arctic. In addition, scientists prepared samples for radiocarbon dating and
other shell geochemical analyses to be conducted upon return to USGS. The radiocarbon chronology and
paleoceanographic reconstructions from the microfauna fossils will provide an unprecedented history of the Ryder
Glacier in Northern Greenland.
Earth Science Matters is produced by the U.S. Geological Survey Land Change Science Program. All content is copyright free, and can be reprinted without permission. Comments, feedback, and suggestions for future stories are welcome. If you would like to subscribe please enter your email address and click the “Subscribe” button on the Program Newsletter page.
U.S. Department of the Interior U.S. Geological Survey
Volume 9, Fall 2019
News from the USGS Land Change Science Program
Earth Science Matters
The Ryder 2019 Expedition allowed USGS scientists to
gather much needed data for their project and to
collaborate with an array of international scientists that
aim to improve understanding of the Arctic and its role in
Earth’s climate. This research will help increase our
understanding of how Arctic glaciers and ice responded to
a warming climate in the past and thus provide insight into
how they may respond to similar warming today and into
the future.
We gratefully acknowledge the support of the Swedish
Polar Research Secretariat, the captain and crew of Oden,
Stockholm University and co-chief scientists Drs. Martin
Jakobsson and Larry Mayer.
Earth Science Matters is produced by the U.S. Geological Survey Land Change Science Program. All content is copyright free, and can be reprinted without permission. Comments, feedback, and suggestions for future stories are welcome. If you would like to subscribe please enter your email address and click the “Subscribe” button on the Program Newsletter page.
U.S. Department of the Interior U.S. Geological Survey
Volume 9, Fall 2019
News from the USGS Land Change Science Program
Earth Science Matters
The threats posed by extreme flooding to many U.S. cities, and nearby infrastructure,
built along rivers are not well constrained due to limited data. For most rivers in the
eastern United States, reliable streamgage measurements extend less than 100 years
and often capture only a handful of the major floods recorded by historic sources (e.g.
newspapers and other written accounts). In order to fill this critical gap, scientists can
study geologic signatures of past flood events buried in coastal sediments. Geologic
reconstructions of past floods can be used to: (1) assess the magnitude of these historic
events, (2) extend records of flooding deeper into the past and (3) identify what drives
changes in extreme precipitation on long timescales. At present, however, few such
reconstructions exist for the eastern United States.
In a recent study, USGS scientists, along with university collaborators from the
College of William and Mary, Woods Hole Oceanographic Institution, University of
Rhode Island and Texas A&M, began to fill this knowledge gap by reconstructing
extreme floods on the Susquehanna River over the past two thousand years. The
Susquehanna has the largest watershed on the U.S. Eastern Seaboard. Sediment core
MD99-2209, collected from the main stem of Chesapeake Bay (water depth = 26
meters) near Annapolis, Maryland by the research vessel Marion Dufresne in 1999,
was analyzed for coarse-grained sediment layers thought to have been deposited
during large floods.
Several such layers were identified downcore. The ages of these ‘paleo-events’ were
determined using lead (210) during the past ~100 years and radiocarbon deeper in the
core. Additionally, the abundance of ragweed pollen increased directly after Colonial
land clearance, providing an additional age marker. The most recent ‘flood’ deposits
found in this core can be attributed to hurricane Agnes (1972) and the Great Flood of
1936. However, many other coarse-grained layers in the sediment core predate
robust historic records and are indicative of prehistoric floods on the Susquehanna
between 1800–1500, 1300–1100, and 400–0 CE. A possible explanation for
increased flood frequency during these intervals is that cooler conditions near
Chesapeake Bay—relative to the tropical North Atlantic—produced favorable
conditions for tropical cyclone development and landfall in the Susquehanna
watershed. Ongoing work, elsewhere in Chesapeake Bay, aims to develop a
complementary record of coastal inundation during intense hurricane strikes in order
to further test this hypothesis.
The paper, “The Mighty Susquehanna—Extreme Floods in Eastern North America
During the Past Two Millennia” was published in Geophysical Research Letters. It
is available at: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GL080890
Earth Science Matters is produced by the U.S. Geological Survey Land Change Science Program. All content is copyright free, and can be reprinted without permission. Comments, feedback, and suggestions for future stories are welcome. If you would like to subscribe please enter your email address and click the “Subscribe” button on the Program Newsletter page.
U.S. Department of the Interior U.S. Geological Survey
Volume 9, Fall 2019
News from the USGS Land Change Science Program
Earth Science Matters
The geologic record includes examples of past climates that were much different from today, and the Eocene epoch
(from 56 to 33.9 million years ago) included the warmest climates of the last 66 million years. During the Eocene, a
series of abrupt warming events, known as “hyperthermals”, coincided with pulses of carbon injection into the
atmosphere, and they are recorded in the geologic record by changes in carbon isotope values. These events had
significant impacts on the distribution of plant and animal communities, and analysis of the events provides insights into
the feedbacks between changes in the global carbon cycle and climate extremes.
The largest hyperthermal event was the Paleocene-Eocene Thermal Maximum (PETM at ~55.5 million years ago), when
a massive amount of carbon was injected into the atmosphere. Carbon injection has been hypothesized to affect the
global hydrologic cycle and seasonal contrasts in temperature, and paleoclimate proxies from sediments deposited during
hyperthermals provide evidence to evaluate those hypotheses.
USGS researchers and colleagues from
Brandon University, Lamont-Doherty Earth
Observatory, and Utrecht University recently
analyzed the impact of hyperthermal events in
the Arctic using sediment cores collected by
the Integrated Ocean Discovery Program
(IODP) Expedition. Analyses of pollen,
biomarkers from soil bacteria, and other
organic-walled microfossils from the sediment
cores allowed the scientists to reconstruct
vegetation, atmospheric temperature, and
hydrology before, during, and after the PETM.
During the Paleocene and early Eocene, the
continents were arranged differently than today
(Figure 1), and the Arctic Basin was more or
less land-locked, with limited exchange
between the Arctic Ocean and the Pacific and
Proto-Atlantic Oceans. The coring site used in
this study, IODP Site 302-4A, is located on
Lomonosov Ridge, a continental fragment that
broke away from the Eurasian continent ~57
million years ago. During late Paleocene-early
Eocene time, the site is thought to have been in
relatively shallow water, and pollen from
nearby landmasses was preserved in the ocean
sediments.
Earth Science Matters is produced by the U.S. Geological Survey Land Change Science Program. All content is copyright free, and can be reprinted without permission. Comments, feedback, and suggestions for future stories are welcome. If you would like to subscribe please enter your email address and click the “Subscribe” button on the Program Newsletter page.
U.S. Department of the Interior U.S. Geological Survey
Volume 9, Fall 2019
News from the USGS Land Change Science Program
Earth Science Matters
Pollen evidence (Figure 2) from the core indicates that late Paleocene
Arctic climates were warmer than today, with mixed conifer-hardwood
forests (with pine, spruce, and walnut) occupying landmasses near the
coring site. Today, these areas are underlain by permafrost, and plant
communities consist of dwarf shrubs, grasses, mosses, and lichens.
Bioclimatic analyses, based on climatic requirements of plant groups
identified in the pollen record, indicate a generally warm late Paleocene
climate (mean annual temperature averaging ~13˚C/55˚F). Independent
analysis of lipid biomarkers also indicates a warm late Paleocene
(14.6˚C/58˚F). In contrast, present day mean average temperatures in
Greenland are currently ~4˚C/39˚F.
During the PETM hyperthermal event, broad-leaved swamp forests (with
members of the cypress family, palms, and other warm temperate to
subtropical plants) dominated the nearby landscape. Both bioclimatic
analyses and biomarkers indicate that PETM mean annual temperatures
increased by as much as 3.5˚C/5.4˚F, driven primarily by warmer winters.
Analysis of other organic microfossils indicates that runoff of water and
nutrients from the continents to the oceans also increased during the PETM, resulting in lower salinity, decreased oxygen
content of water, and changes in algal communities in the Arctic Ocean.
After the peak of the PETM, forested wetland and lowland vegetation dominated the landscapes, and subtropical plants
were absent. Mean annual temperatures decreased but remained warmer than the late Paleocene baseline, and normal
marine conditions returned.
The study shows that the PETM injection of carbon to the atmosphere was accompanied by a significant warming of air
temperatures, particularly during the winters. The resulting restructuring of plant and animal communities includes the
northernmost known occurrence of palms and other taxa that are now native to tropical and subtropical latitudes.
Increased runoff of water and nutrients from the land to the ocean resulted in lower salinity and availability of oxygen in
ocean waters, which affected the composition of algal communities that are the base of the marine food chain.
This research is part of a broader international effort to document the interactions between natural changes in greenhouse
gas concentrations, climate, and plant and animal communities on land and in the ocean across the globe. Through
studies of past abrupt events, earth scientists are developing large datasets that can be used to test results of global
climate models that simulate past, present, and future climate. The results also provide a unique window on how the
Earth system has responded to extreme events of the past - yielding insights on impacts of potential changes in the
future.
The paper “Arctic vegetation, temperature, and hydrology during Early Eocene transient global warming events” was
published in Global and Planetary Change and is available here: https://www.sciencedirect.com/science/article/pii/
S0921818119300979?via%3Dihub
Earth Science Matters is produced by the U.S. Geological Survey Land Change Science Program. All content is copyright free, and can be reprinted without permission. Comments, feedback, and suggestions for future stories are welcome. If you would like to subscribe please enter your email address and click the “Subscribe” button on the Program Newsletter page.
U.S. Department of the Interior U.S. Geological Survey
Volume 9, Fall 2019
News from the USGS Land Change Science Program
Earth Science Matters
It seems remarkable that, in the 21st Century, we still don’t fully understand why trees die during drought. Developing
this understanding is key if we are to maintain healthy forests, along with their invaluable goods and services. This is
especially true as droughts are expected to become more frequent and severe. Recent research in this area has mostly
focused on two proposed mechanisms of drought-induced tree death: hydraulic failure (dehydration) and carbon
starvation (metabolic collapse). Both mechanisms can kill trees directly or contribute to tree death indirectly by making
trees more vulnerable to natural enemies like insects. Regardless, it is widely accepted that the most physiologically
stressed trees will be the ones that die during drought. That said, recent research indicates a weak relationship between
metrics related to physiological stress and tree death during drought. Something else must also be going on…but what?
Part of the answer to this question is being unraveled in the forests of California’s Sierra Nevada where USGS research
scientists have tracked the fates of tens of thousands of trees annually for 37 years. Every year, newly-dead trees get
“autopsied” to delineate cause of death. One such example is bark removal that reveals characteristic galleries (tunnels)
left by tree-killing bark beetles (Figure 1).
During California’s historically unprecedented 2012-2016 drought, some 2,000
monitored trees died and received autopsies, providing a unique window into
mechanisms of drought-related tree death. The majority of the dead trees were killed
by native bark beetles however, the size and stress level of trees that were killed
depended heavily on the particular tree
preferences of different bark beetle species
as demonstrated in Figure 2. Thus, even
during such an extreme drought, substantial
proportions of stressed trees survived
because their size was one that mostly
avoided fatal beetle attack. Conversely,
substantial proportions of comparatively
unstressed trees died because they were of a
size selectively killed by outbreaking
beetles. That is, idiosyncratic tree selection
by bark beetles meant that tree stress was
only weakly related to tree death.
These findings shine a spotlight on what scientist and author E.O. Wilson calls
“the little things that run the world”, in that the small size of insects and other
invertebrates belies their overwhelming importance in shaping our world Figure
3). The findings further suggest that, even during extreme droughts formerly
thought to kill trees directly (by hydraulic failure or carbon starvation), tree
survival in selected areas might be substantially enhanced by controlling bark
beetle populations. Targeted control methods have already been developed for a
Earth Science Matters is produced by the U.S. Geological Survey Land Change Science Program. All content is copyright free, and can be reprinted without permission. Comments, feedback, and suggestions for future stories are welcome. If you would like to subscribe please enter your email address and click the “Subscribe” button on the Program Newsletter page.
U.S. Department of the Interior U.S. Geological Survey
Volume 9, Fall 2019
News from the USGS Land Change Science Program
Earth Science Matters
few particularly damaging bark beetle species, providing “proof of
concept” which may help future efforts to maintain healthy forests.
Furthermore, this research highlights the need to find targeted control
methods for each species in a highly diverse array of bark beetles.
The paper, “Which trees die during drought? The key role of insect host
-tree selection” was published in Journal of Ecology and is available
here: https://besjournals.onlinelibrary.wiley.com/doi/abs/10.1111/1365-
2745.13176
Earth Science Matters is produced by the U.S. Geological Survey Land Change Science Program. All content is copyright free, and can be reprinted without permission. Comments, feedback, and suggestions for future stories are welcome. If you would like to subscribe please enter your email address and click the “Subscribe” button on the Program Newsletter page.
U.S. Department of the Interior U.S. Geological Survey
Volume 9, Fall 2019
News from the USGS Land Change Science Program
Earth Science Matters
Monitoring and understanding land-use change in America is critical given our continued growth, urbanization, and
dependence on natural resources. To achieve more accurate assessments of urban land changes, USGS scientists from
the Patterns in the Landscape – Analyses of Cause and Effect (PLACE) team employed two decades of satellite data to
interpret and study landscape change across the conterminous United States from 1992-2011.
Beginning in 2015, a small group of geographers came together to improve United States urban land maps by making
adjustments to multidecadal, national-scale land-use maps produced by the National Land Cover Database (NLCD).
NLCD has been the seminal source for wall-to-wall land-use/land-cover maps of the country, and part of the NLCD
effort centers on mapping developed lands. Existing change estimates generated by NLCD and others covering the 1990s
and early 2000s represent the best available data for land managers and other researchers, but uncertainties remained.
Early in their exploratory effort, the PLACE team determined that rural roads included in the developed classes of
NLCD maps were problematic due to inconsistencies in road location, density, and continuity. In addition, some
classification techniques associated with rural areas and impervious surfaces contributed to artificial increases in areas
classified as developed. To mitigate these challenges, scientists hypothesized that a series of post-processing techniques
could effectively improve the NLCD maps spanning the years 1992-2011. The team edited and removed rural roads in
the NLCD developed class by intersecting a suite of geospatial land use data and manually removing misclassified areas.
Their efforts resulted in higher accuracy maps of urban land and improved urban change estimates spanning a 19-year
period.
The removal of roughly 230,000 square kilometers of rural roads from the NLCD developed class resulted in maps that
better characterize the urban footprint, with a national accuracy approaching 99 percent in 2001 and 2006. These urban
maps provide improved inputs for modeling applications and policy decisions that rely on quantitative and spatially
explicit information regarding urban lands.
Examples of before and after maps for urban areas of Atlanta, GA and Houston, TX are shown in Figure 1. Since their
publication, the revised maps have been used in peer-reviewed land-use forecasting efforts and by the NLCD team to
help develop its 2016 land-use/land-cover map. Additionally, USGS researchers are actively using these data to develop
annualized urban maps for California to further refine our communal understanding of contemporary land use changes in
the West.
By creating novel protocols to improve existing land cover data, the resulting maps contribute to an improved national
urban map repository. These efforts advance our understanding of the rates and causes of land change in the United
States while helping managers and stakeholders make more informed decisions to better prepare for the future.
The paper, “Removing Rural Roads from the National Land Cover Database to Create Improved Urban Maps for the
United States, 1992 to 2011”, was published in Photogrammetric Engineering & Remote Sensing and was recognized as
the third-place recipient of the 2019 ESRI Award for Best Scientific Paper in Geographic Information Systems. It is
available at: https://pubs.er.usgs.gov/publication/70195240. Geospatial data are also available at: https://doi.org/10.5066/
F79G5K05.
Earth Science Matters is produced by the U.S. Geological Survey Land Change Science Program. All content is copyright free, and can be reprinted without permission. Comments, feedback, and suggestions for future stories are welcome. If you would like to subscribe please enter your email address and click the “Subscribe” button on the Program Newsletter page.
U.S. Department of the Interior U.S. Geological Survey
Volume 9, Fall 2019
News from the USGS Land Change Science Program
Earth Science Matters
Earth Science Matters is produced by the U.S. Geological Survey Land Change Science Program. All content is copyright free, and can be reprinted without permission. Comments, feedback, and suggestions for future stories are welcome. If you would like to subscribe please enter your email address and click the “Subscribe” button on the Program Newsletter page.
U.S. Department of the Interior U.S. Geological Survey
Volume 9, Fall 2019
News from the USGS Land Change Science Program
Earth Science Matters
The northern range limit of most
tropical plants and animals is
determined by extreme freeze
events. In coastal wetlands along
the Gulf of Mexico and Atlantic
coasts of the United States,
freeze events govern the northern
extent of mangrove forests.
Many climate model simulations
indicate that winter temperatures
may warm in the coming
decades; if that were to occur, it
is likely that tropical, freeze-
sensitive mangrove forests would
expand northward at the expense
of temperate, freeze-tolerant salt
marshes. To better anticipate and
prepare for potential mangrove
range expansion, there is a need
to advance understanding of the
influence of microclimate.
Macroclimate refers to climatic
conditions that occur across very
large spatial scales (i.e., typically
up to 100 km horizontally and 10 km vertically). In contrast, microclimate refers to climatic conditions that vary across
much smaller spatial scales (i.e., typically less than 100 m horizontally and less than 10 m vertically). While
macroclimate is governed primarily by continental-scale atmospheric circulation systems, microclimate is also regulated
by local factors near the earth’s surface including proximity to vegetation, soil, and water.
A recent study by USGS scientists and Florida International University synthesized hypotheses regarding the effects of
microclimatic variation on temperature gradients and corresponding mangrove freeze damage. Temperature data from
the literature and from temperature loggers placed in the field were used to quantify temperature gradients produced by
microclimatic factors. Then, literature-derived mangrove freeze damage data were used to quantify the ecological effects
of these temperature gradients. Microclimatic gradients due to local factors (e.g., proximity to water, soil, or vegetation)
can determine whether temperatures are below or above a threshold at which mangrove damage and/or mortality will
occur. For example, temperatures during a freeze event may be warmer near the ocean, close to the soil surface, and
beneath the canopy of larger mangroves; thus, these are areas where mangrove freeze damage and mortality may be
reduced by microclimatic conditions.
Earth Science Matters is produced by the U.S. Geological Survey Land Change Science Program. All content is copyright free, and can be reprinted without permission. Comments, feedback, and suggestions for future stories are welcome. If you would like to subscribe please enter your email address and click the “Subscribe” button on the Program Newsletter page.
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Volume 9, Fall 2019
News from the USGS Land Change Science Program
Earth Science Matters
The paper identifies the following six
microclimatic factors, which produce
air temperature gradients that
influence mangrove responses to
winter temperature extremes: (1)
distance from the ocean; (2) distance
from wind buffers; (3) mangrove
canopy cover; (4) height above the
soil surface; (5) local slope concavity;
and (6) tidal inundation. Variation in
these factors produces local
temperature differences that range
from 2 to 14°C, with associated
effects on horizontal and vertical
patterns of biological damage from
freezing. These results clarify the
influence of microclimate on spatial
patterns of biological damage and
mortality due to winter temperature
extremes.
The largest temperature gradient
observed was related to distance from the soil surface. During chilling and freezing events, temperatures were ~9-14°C
warmer near the soil surface compared to temperatures at just one meter above the soil surface. These observations
indicate that there is a protective buffer zone near the soil surface, in which mangrove propagules, roots, and above-
ground material are more protected from freeze effects compared to taller plant sections that are exposed to colder air.
As mangroves expand into new areas in response to warming winter temperatures, the protective buffer zone near the
soil surface will likely play a critical role to promote ecological resilience. If the newly-arrived individuals can grow and
reach the reproductive stage, there is a good chance that their propagules and low-lying plant strata will be thermally
protected and able to rapidly regenerate following winter temperature extremes. As mangrove ranges expand in response
to climate change, microclimatic variation is expected to produce both adverse environments where mangrove expansion
is prohibited and expansion hot spots where mangroves are protected. Subsequent expansion into newly-available habitat
will occur from protection zones, and microclimatic gradients may even produce positive feedback cycles that ultimately
accelerate the rate of range expansion in response to warming. Collectively, these findings regarding the role of
microclimate can improve predictions of mangrove range expansion in response to changing macroclimate.
The paper “Microclimate influences mangrove freeze damage: implications for range expansion in response to changing
macroclimate” was published in Estuaries and Coasts and is available here: https://link.springer.com/article/10.1007%
2Fs12237-019-00533-1