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Global Change Impacts in Nature Reserves
in the United States 1
Thomas J. Stohlgren 2
Abstract-Large natural areas such as national parks, forests, and
wildlife reserves have provided the U.S. Global Change Research
Program with an important outdoor laboratory that provides an
index of change in our most treasured ecosystems. Rapidly changing
climates are superimposed on other ecosystem stresses such as
urbanization, air pollution, habitat fragmentation, loss of native
biodiversity, and the invasion of exotic species. Climate influences
the frequency and intensity of disturbance (e.g. fire and insect
outbreaks), species distribution patterns, hydrological patterns,
and forest condition. I present examples of research and monitoring
activities on Department of the Interior lands, primarily in the
western United States. Evidence of regional warming comes from
rapidly disappearing glaciers in Montana, lake level decline in
Crater Lake, Oregon, and expansion of high-elevation forests in
Colorado and Washington. I also present evidence of regional
cooling in the summer months due to land-use changes in the plains
of Colorado, where crop irrigation and landscaping have influenced
the climate, hydrology, and forest vegetation patterns in the adjacent
Rocky Mountains. In some areas, the effects ofland-use practices on
regional climate may overshadow larger-scale temperature changes
commonly associated with observed increases in CO 2 and other
greenhouse gases. Our understanding of rapid climate change, and
other equally important multiple stresses to forest condition, is
aided by strong ecosystem research and long-term monitoring
programs. Our challenges in North America (and the world) are to:
(1) determine which species, habitats, and ecosystem processes are
most sensitive to rapid environmental change and multiple stresses;
(2) monitor ecosystem change in consistent and comparable ways;
and (3) coordinate mitigation strategies and efforts.
Protection Agency, National Aeronautics and Space
Administration, National Science Foundation, Smithsonian
Institution, and Tennessee Valley Authority (National
Science and Technology Council 1997). Key research areas
include ozone depletion, seasonal to inter-annual variations
in climate, climate forcing, climate change over decades to
centuries, detection and attribution of climate change,
terrestrial and aquatic ecosystem feedbacks and effects,
land cover and land use, and climate effects on marine
ecosystems.
The U.S. Geological Survey portions of the USGCRP
involve many research projects ranging from studies of sealevel rise to changing bird populations and wetland habitat
loss (Figure 1). Summarizing the research of all these sites
is beyond the scope of this paper. Within the Biological
Resources Division ofthe USGS, the global change research
program focuses primarily on terrestrial ecosystem research
and multiple stresses to USDI lands including climate
change, human population growth and land-use change, air
and water pollution, habitat fragmentation, altered
disturbance regimes, and invasive species (Figure 2).
Examples of Global Change
Research on Department of
Interior Lands
In this section, I provide selected examples of global
change research primarily conducted on national parks and
monuments, wildlife reserves, and national resource areas
managed by the Department of the Interior. In Sequoia,
Natural areas set aside to conserve natural resources and
protect biological diversity also serve as outdoor laboratories.
They are ideal for moni toring ecological processes that act on
long temporal scales such as climate change, long fire return
intervals, and periodic droughts. They provide an index of
change in our most treasured ecosystems and a comparison
to the more heavily altered landscapes in which most of us
live. They provide us with unparalleled opportunities for
research and public outreach.
The U.S. Global Change Research Program (USGCRP) is
a multi-faceted program involving several Federal agencies
including the Departments of Agriculture, Commerce,
Defense, Energy, and the Interior, the Environmental
Ipaper presented at the North American Science Symposium: Toward a
Unified Framework for Inventorying and Monitoring Forest Ecosystem
Resources. Guadalajara, Mexico, November 1-6, 1998.
2Thomas J. Stohlgren is an ecologist atthe with the U.S. Geological Survey,
Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO 80523-1499, U.S.A. Phone: (970) 491-1980; Fax: (970) 491-1965;
Internet: Thomas_Stohlgren@USGS.gov
USDA Forest Service Proceedings RMRS-P-12. 1999
Figure 1.-Map of U.S. Geological Survey global change research
sites.
5
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Northwest Ecosystems
Crater
Sierra NeVli()CA
'--/'-'-' .
"T-"r<>'
. .~~:::\j--~.-.~
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Figure 2.-Map of selected terrestrial ecosystem sites in the U.S. Geological Survey's global change
research program.
Kings Canyon, and Yosemite National Parks in California,
for example, ongoing studies on paleoecology, forest
dynamics, and forest modeling are determining how changes
in clima te affect the frequency and size ofwildfires (Swetnam
1993, In Preparation). The research developed tree-ring
climatology techniques on long-lived giant sequoia
(Sequoiadendron giganteum), and improved insights into
fire frequencies over the past 5,000+ years. More
importantly, resource managers now have detailed maps of
areas most influenced by recent decades of fire suppression
as a basis to set priorities for prescribed burning.
In Glacier National Park; Montana, observations that
some glaciers have receded at alarming rates over the past
few decades have sparked ecosystem-wide interdisciplinary
studies of climate, hydrology, and vegetation. Spatial models
of snowmelt, forest growth, and soil moisture provide a basis
to understand forest species distributions and change (Fagre
In Press). In Crater Lake, Oregon, scientists are monitoring
lake level decline in recent years, reminiscent of the severe
droughts of the 1930's (G. Larson, personal communication).
In Olympic National Park and adjacent lands, detailed
monitoring offorest dynamics has shown increased migration
of subalpine trees into meadows and forest openings in
response to recent climate warming (Peterson 1994).
Dendrochronology techniques comparable to those used
throughout the western U.S. are adding to a regional and
sub-continental understanding of climate change.
In the Great Basin, studies are linking climate change and
land-use change with well-replicated experiments using
rain shelters and various grazing regimes to assess potential
changes to plant species composition and diversity (Pike and
Borman 1993). In the southwestern U.S., research is focusing
on tree-ring climate reconstruction on the shrub and
grassland ecotones (Woodhouse 1997), and on monitoring
the effects of climate change on invasive plant species
6
(Huenneke 1997). In the Central Grasslands, scientists are
modeling vegetation change under various climate change
scenarios (Neilson 1995).
The Colorado Rockies Global
Change Research Program
I now provide a case study of the ecosystem-scale global
change research program that I have coordinated for seven
years. The research team was selected to include climate
modelers, plant ecologists, geographers, and hydrologists to
assess the effects of climate and land-use change in the
Rocky Mountains of Colorado. Our scientific goal is to
develop a better understanding ofregional climatelhydrologic
patterns and species-environment relationships to determine
which species, habitats, and ecosystem processes are most
sensitive to rapid environmental change and multiple
stresses. Our resource management emphasis continues to
provide timely, scientific data to meet the high priority
needs of resource managers. In the first seven years of the
research program (1991-1998), we developed a basic
understanding of vegetation change, climate change, and
hydrologic change as described below.
Evidence of Vegetation Change
We developed an understanding of forest distributions,
productivity, and disturbance patterns. Our research team
produced solid evidence that the growth rates of krummholz
(wind-trimmed low-growing trees) have increased in the
forest-tundra ecotone of Rocky Mountain National Park
(Baker et al. 1995). Substantial tree invasions into openings
between patches of subalpine forest have been documented
(Baker and Weisberb 1995; Weisberg and Baker 1995). Our
USDA Forest Service Proceedings RMRS-P-12. 1999
field studies also showed that forested ecotones (i.e.,
boundaries between forest types) are sensitive to changes
in regional climate (Stohlgren and Bachand 1997). We
established 14 long-term vegetation transects (20m x 200m+)
as "ecological time capsules" to monitor vegetation
distribution changes and the invasion of exotic plant species
(Stohlgren et al. 1998a, In Press).
The analysis of climatic variation on fire regimes in the
montane zone of the Front Range over the past 400 years
showed that fire occurrence is extremely sensitive to climate
(Mast 1993; Veblen et al. 1994; Mast et al. 1997, In Press).
During severe droughts that occur approximately once per
century, nearly half of the entire montane zone burns during
a single year. Fire in the montane zone would likely increase
due to greater climatic variability. Tree-ring studies show
that when years of above-average precipitation are followed
by springs and summers of below-average precipitation
there is an increase in the area burned. Such periods of
extreme climatic variability at time scales of two to four
years are closely linked to EI Nino Southern Oscillation
events which yield strong signals in the tree-ring record of
fires in the Front Range (Veblen In Press). Since
approximately 1915, fire suppression has created major
changes in Front Range ecosystems, including forest
structures that are more susceptible to catastrophic wildfires,
or more likely to occur under future scenarios of warmer and!
or more variable climates (Mast 1993; Veblen et al. 1994;
Mast et al. 1997, In Press).
Evidence of Climate Change
Colorado State University's Regional Atmospheric
Modeling System (RAMS; (Pielke et al. 1994, In Press)
results suggest that the Rocky Mountains, with extreme
elevation and vegetation gradients, are very sensitive to
regional and global climate change (Copeland et al. 1996a,b;
Chase et al. 1996). Land-use practices in the plains influence
regional climate and vegetation in adjacent natural areas in
the mountains in predictable ways (Chase et al. In Press).
Modifications to natural vegetation on the plains, primarily
due to agriculture and urbanization, produce a regional
cooling effect expressed as lower summer temperatures in
the mountains. Combined, the mesoscale atmosphericllandsurface model results, short-term trends in regional
temperatures, forest distribution changes, and streamflow
data indicate that the effects ofland-use practices on regional
climate may overshadow larger-scale temperature changes
commonly associated with observed increases in CO 2 and
other greenhouse gases (Stohlgren et al. 1998b). Regional
model simulations on seasonal time scales demonstrate a
significant sensitivity of regional weather, and therefore
climate, to land-use change (Chase et al. In Press; Pielke et
al. In Press).
Evidence of Hydrological Changes
Paleo-clima te records contained in lake sediments provide
evidence that biological and geomorphological processes in
USDA Forest Service Proceedings RMRS-P-12. 1999
high elevations of the Rocky Mountains have been very
responsive to climatic variability in the past 12,000 years.
Evidence of changes caused by temperature variability and
shifts in the amount and seasonality of precipitation are
found in debris flow frequency and movement of vegetation
up and down an elevation gradient (Menounos 1994, Reasoner
1996).
Ecosystemlhydrology models suggest that land cover and
climate change influence different parts of the Rocky
Mountains and plains in complex ways, depending on loca tion,
climate, and topography (Lammers et al. 1997). Land cover
change exerted stronger controls on plant productivity and
water fluxes to the atmosphere than temperature changes in
low-elevation foothills and grasslands. In contrast,
temperature was a more important influence on water
fluxes and plant productivity in high-elevation coniferous
forests and tundra. In high-elevation watersheds, cooling or
warming had a great influence on the timing of snowmelt
(Baron et al. 1997a, 1998, In Press). More importantly, the
long-term data set from Loch Vale watershed (Baron et al. In
Press), shows a steady increase in nitrogen deposition (3 to
4 kg/ha/yr N) from air pollution, which along with climate
change, has enormous potential to affect stream biota,
native plant species, and water quality (Baron et al. 1997b).
Proposed Future Research
Now that baseline climate, hydrology, and vegetation data
are available, future research is designed to evaluate multiple
stresses, including rapid environmental change, that affect
the management of key natural resources and processes in
Rocky Mountain National Park and the region (Figure 3).
Our interdisciplinary approach to ecosystem science will
address high priority issues such as: (1) providing better
climate change scenarios to land managers to assess the
''vulnerabilities'' of ecosystems to rapid environmental
change; (2) assessing how climate change influences air
quality values (visibility and pollution) in Class I airsheds
(e.g., Rocky Mountain National Park); (3) quantifying
climate change and nitrogen deposition effects on water
quantity and delivery, water quality, and aquatic diversity;
(4) developing GIS-based disturbance history maps (fire
and insect outbreaks) to aid the Park's Fire Management
Program; and (5) determining how climate change,
vegetation management practices, and disturbance affect
key wildlife habitat (e.g., aspen) and the spread of exotic
plant species (Figure 3).
Our proposed synthesis involves partnerships with several
USGS Global Change Research Programs (Glacier, Olympic,
Sequoia, Central Grasslands), other U.S. Geological Survey
research and monitoring programs, Long-Term Ecological
Research Sites, and many Bureau of Land Management,
National Park System, and U.S. Fish and Wildlife Service
management units to assess regional patterns of climate
change, exotic plant invasions, air pollution, and disturbance
effects. The ongoing synthesis of these studies is assessing
the interaction between land-use change, regional
vegetation distribution, mesoscale climate, and hydrology
(Stohlgren et al. 1998b).
7
Phase II: Resolving High Priority
Resource Management Issues
I • -
Phase I: Developing Basic
Understanding of the Ecosystem
Air Pollution
Transport &
Effects on
Air Quality
•I
Assessing
"Vulnerabilities"
of Key Resources
• to Rapid
Environmental
. . .I--:-i Change
•
Invasion of
Exotic Plant
Species
Nitrogen
Effects on
Water Quality/
Stream Biota
Effects of
Effects of
Grazing and
. .. -____~ Other ManAltered
Disturbance
agement
Regimes
Practices
Figure 3.-Schematic diagram of Phase I (1991-1998) and Phase II (1999-2003) of the global
change research program in the Colorado Rockies Biogeographical Area.
Challenges of Future Global
Change Research in Nature
Reserves in the U.S.
There are several positive aspects of the global change
research programs in na ture reserves in the U. S. The various
agencies involved have expressed a long-term commitment
to the programs, many of which have maintained funding
since 1991. The research is based on scientific peer-review of
proposals, and periodic program reviews. Continued funding
is contingent on the quality and relevancy of the science,
meeting the needs ofland managers, scientific productivity,
and public outreach. In fact, all projects in the USGS Biological
Resources Division's Global Change Research Program are
currently re-competing for funding, so Figure 2 may look
different in the near future.
There are, however, many ways in which the global change
programs can be improved. Greater efforts must be made to
standardize many of the methods used to increase the
comparability of data, not only among the Department ofthe
Interior programs, but with other agencies and research
programs (e.g., LTER sites, U.S. Department of Agriculture
Forest Health Monitoring). Also, a greatly expanded network
of global change research and long-term monitoring sites is
needed to assess multiple stresses at local, regional, and
national scales. Despite strong individual research projects,
many ecosystems in the U.S. are not now being closely
monitored in consistent ways. Thus, it is difficult to assess
cumulative effects or regional impacts of forest distribution
changes, altered disturbance regimes, altered hydrological
regimes, habitat loss, or the invasion of exotic species.
Certainly, much work lies ahead. An additional positive
step in global change research in the U.S. is the current
Congressionally mandated "National Assessment of Global
8
Change," under which agency and academic scientists are
working closely with regional stakeholders (e.g., from
agriculture, energy industry, ranching, recreation) to
strengthen existing efforts. The report to Congress is due
January 1, 2000, but the process has already led to better
understanding and communication among scientists,
stakeholders, and the public.
Conclusion ------------------------------Just as better coordination is needed among U.S. global
change research programs, better coordination of
international research and monitoring could be mutually
beneficial. Our challenges in North America (and the world)
are to: (1) determine which species, habitats, and ecosystem
processes are most sensitive to rapid environmental change
and multiple stresses; (2) monitor ecosystem change in
consistent and comparable ways; and (3) coordinate
mitigation strategies and efforts. Sharing expertise, data,
models, and model program designs is the first step. Creating
an expanded network of monitoring sites with comparable
data collection remains our most significant challenge.
Acknowledgments
Many colleagues contributed to the ideas and examples
presented in this paper. Jill Baron, Roger Pie Ike Sr., Dan
Binkley, Tim Kittel, Tom Veblen, Bill Baker, and Tom Chase
are co-investigators in the Colorado Rockies Global Change
Research Program, and they continue to educate me. Funding
for this research is provided by the U.S. Geological Survey
with logistical support provided by the Midcontinent
Ecological Science Center (USGS) and the Natural Resource
Ecology Laboratory at Colorado State University. Michelle
USDA Forest Service Proceedings RMRS-P-12. 1999
Lee, April Owen, and Geneva Chong provided helpful
comments to an earlier version ofthe manuscript. To all I am
grateful.
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