Changes in Ecosystems
USGCRP Fiscal Years 2004-2005 Accomplishments

USGCRP
Program Elements

Atmospheric Composition

Ecosystems

Global Carbon Cycle

Decision-Support Resources Development and Related Research on Human Contributions and Responses

Climate Variability and Change

The Global
Water Cycle

Observing and Monitoring the Climate System

Communications

International Research and Cooperation

The following are selected highlights of recent research supported by CCSP participating agencies (as reported in the fiscal year 2006 edition of the annual report, Our Changing Planet).

EIWG-Sponsored Workshop on Priority Setting for Ecosystems Research in CCSP

The EIWG sponsored a workshop, held in February 2004 in Silver Spring, Maryland, that brought together a diverse group of 70 scientists from U.S. universities, research centers and institutes, and Federal agency research programs in a "think tank" atmosphere for 3 days. The specific objective was to identify and articulate priorities and approaches for research under Chapter 8 of the CCSP Strategic Plan . Although the EIWG organized and funded it, the workshop was run by a steering committee from the science community. The workshop report is due in the winter of 2006 and will be available on the CCSP Web site.

Convergence in Ecosystem Water Balance over Continental Scales [9]

Water availability limits plant growth and production in almost all terrestrial ecosystems, but biomes differ substantially in sensitivity of aboveground plant growth, or aboveground net primary production (NPP). A recent synthesis building on over 10 years of productivity data from 14 sites in North America showed that rainfall-use efficiency decreased across biomes as mean annual precipitation increased. However, during the driest years at each site, there was convergence to a common maximum value typical of arid ecosystems. In years when water was most limiting, deserts, grasslands, and forests all exhibited the same rate of biomass production per unit rainfall, despite differences in physiognomy and site-level differences in efficiency. Incorporating this information into ecosystem models will improve forecasts of future ecosystem behavior in the face of climate change.

Global Patterns in Human Appropriation of Net Primary Production [10]

Biophysical models were used in conjunction with data from the United Nations Food and Agriculture Organization to estimate the annual amount of Earth's terrestrial NPP or plant growth that humans require for food, fiber, and fuel using the same modeling architecture as satellite-supported NPP measurements. The amount of Earth's NPP required to support human activities is an aggregate measure of human impacts on the biosphere and an indicator of societal vulnerability to climate change. The amount of human-appropriated NPP (HANPP) for each country was calculated on a per capita basis for products consumed and then projected onto a global map of population to create a spatially explicit map of NPP-carbon "demand" (see Figure 20). The HANPP map was compared to a map of "supply" derived from Advanced Very High-Resolution Radiometer data from satellites. It was found that humans consume 20% of Earth's total NPP on land, with regional balances ranging from 6% consumed in South America to over 70% consumed in Europe and Asia, and local balances ranging from near 0% (central Australia) to over 30,000% for major urban areas (e.g., New York City). The uneven distribution of NPP supply and demand indicates the degree to which countries rely on NPP "imports" and suggests options for slowing future growth in NPP demand.

Ocean Photosynthesis from Space [1]

The rate of photosynthesis for a given area is determined by its biomass of living plant material, the plants' growth rates, and the availability of sunlight. Until now, quantifying photosynthetic rates over large ocean areas has been difficult, if not impossible, because growth rates could not be characterized from space. The path to solving this problem is to use ocean color data analysis – specifically the application of partial wave analysis – that permits estimates of both the carbon biomass of ocean plants and their growth rates. This development will make it possible to use satellite remote sensing to improve estimates of ocean photosynthesis and detect changes over time.

Warming Interactions with Soil Carbon and Nitrogen in the Arctic Tundra [12]

Research results from the Arctic tundra in Alaska demonstrated how warming and consequent release of nutrients from increasingly decomposing soil organic matter will feed back positively and lead to increasing carbon losses from tundra soils. Data from a 20-year fertilization experiment showed that increased nutrient availability caused a net ecosystem loss of almost 2,000 gC m -2 (a 21% reduction over the 20-year period), even though annual aboveground plant production doubled, because of losses of carbon and nitrogen from deep soil layers. The results suggest that projected releases of soil nutrients associated with high-latitude warming may further amplify carbon release from soils, causing a net loss of ecosystem carbon and a positive feedback to climate warming.

Effects of Nitrogen Deposition on Water Quality and Carbon Sequestration [16]

Human effects on the natural cycling of nitrogen have caused significant alterations of land productivity, freshwater quality, and marine ecosystems. Nitrogen compounds generated by human activities are transported by the atmosphere and deposited onto ecosystems. Healthy forests remove much of the deposited nitrogen, storing it in plant tissues. In the Chesapeake Bay watershed, for example, forests retain 88% of deposited nitrogen, allowing only about 1 kg ha -1 yr -1 to leach into aquatic ecosystems (see Figure 21). As the level of deposition rises, the percentage of nitrogen retained declines and the amount of nitrogen released into downstream ecosystems increases. Nitrogen deposition will increase productivity in terrestrial ecosystems that are nitrogen deficient. Net carbon uptake by forests of the mid-Atlantic region could increase by 25% from nitrogen deposition; however, this rate of increase may be reduced by ground-level ozone pollution, which is damaging to many plant species.

Ecosystem Warming Facility Constructed and Operational

An ecosystem warming experimental facility was constructed in a boreal forest in northern Manitoba, Canada, and began operation during FY 2004. The facility exposes trees and soils to temperatures 5°C above ambient to examine potential effects of warming on northern forests. Preliminary (FY 2004) data show acclimation of soil respiration to warming such that the rate of respiration (CO₂ release) following warming was about the same as the rate prior to warming, indicating a nearly complete acclimation to warming in the belowground component of the ecosystem. This result, if corroborated by continued data collection in FY 2005 and beyond, has important implications for understanding a potential positive feedback on global warming caused by increased soil respiration in northern ecosystems (i.e., such a positive feedback might not occur in all ecosystems). In the warmed plots, tree growth began earlier in the spring and the growth of understory plants was greatly increased. Such changes in plant growth and its seasonal timing are important to the energy balance of northern ecosystems as the climate warms, and could result in a positive feedback to warming. Early results indicate greater carbon gains in the warmed plots relative to the ambient plots. For more information on this facility, see the Department of Energy's Program for Ecosystem Research.

Elevated Carbon Dioxide Effects on a Florida Ecosystem [8]

A study of a Florida scrub oak forest ecosystem suggested for the first time that the abundance of a trace element influenced the response of vegetation to elevated CO₂ . The response of a nitrogen-fixing plant to elevated CO₂ declined over a 7-year period. The decline was strongly correlated to a decline in molybdenum, an element required for producing a key enzyme that affects nitrogen uptake by plants. The work illustrates that plant responses to elevated CO₂ may be highly species-specific. It also raises the possibility that the expected increase in plant growth due to elevated CO₂ could be limited by the availability of nitrogen.

Effects of Climate Change on Eastern U.S. Bird Species [14]

An atlas was produced that documents the current and potential future distribution of 150 common bird species in the eastern United States in relation to climate and vegetation distributions. Distribution data for individual species were derived from the Breeding Bird Survey from 1981 to 1990. Models were developed that related distributions of individual bird species to environmental variables (tree species abundance, climate variables, and elevation variables). Two scenarios of global climate change were then used to project potential changes in the distributions of the bird species. Depending on the global climate model used, as many as 78 bird species are projected to decrease by at least 25%, while as many as 33 species are projected to increase in abundance by at least 25% due to climate and habitat changes (see Figure 22 for an example).

Climatic Variability, Ecosystem Dynamics, and Disturbance in Mountain Protected Areas [2, 3, 4, 5, 7, 17, 18]

Northwestern mountain ecosystems play an important role in shaping the economies and landscape development of the region and provide services such as water purification and storage, and recreational opportunities. A project was initiated to quantify how the hydrological and ecological aspects of these ecosystems respond to climatic variability and large-scale landscape disturbance by examining past responses and projecting possible future outcomes of ongoing climatic change. The research project, Climate-Landscape Interactions on a Mountain Ecosystem Transect (CLIMET), was carried out across a transect of mountain systems along gradients of maritime to continental climate and decreasing landscape fragmentation (Olympic National Park, North Cascades National Park, and Glacier National Park) (Fagre and Peterson, 2002). The project has provided information on glacial decline, alpine forest changes, and ecological responses to climate variability (Fagre et al ., 2003). For example, an analysis of digital aerial photography and historical data documents that the number of glaciers in Glacier National Park has dropped from an estimated 150 in 1850 to 27 present today. The largest glaciers are, on average, only 28% of their previous size (see Figure 23). Future glacial recessions and vegetation distributions were projected using a geospatial modeling approach. Projections indicate that the largest glaciers will be gone in the northern Rocky Mountains by the year 2030 if current rates of warming continue (Hall and Fagre, 2003). The loss of glaciers in mountain watersheds will change the timing and amount of stream discharge and affect aquatic organisms dependent on cold waters.

Data are becoming available on the response of mountain ecosystems to climatic variability, particularly to multi-decadal trends in moisture. One such long-term pattern is the Pacific Decadal Oscillation (PDO), a period of above- or below-average sea surface temperatures in the Pacific Ocean that influences climate in the northwest part of North America. Mountain snowpacks in Glacier National Park track the PDO very closely and show regular 20- to 30-year periods of greater and lesser snow cover (Selkowitz et al ., 2002). These patterns explain glacier fluctuations and periods of increased tree growth in the northern Rocky Mountains (Pederson et al ., 2004). The frequency and size of forest fires in the Pacific Northwest also show a clear response to the PDO (Hessl et al ., 2003). Analysis of tree ring widths from drought-sensitive trees indicates that such multi-decadal oscillations have had an influence on these mountain environments for the past 500 years or more (Gedalof et al ., 2005). Such results suggest that it may be possible to forecast general mountain ecosystem responses to continuing climatic oscillations.

Sensitivity of Forests in Northern California to Climate and Fire Regime Variation [19, 21]

Often, fire appears to serve as a catalyst for change during periods of rapid climate change. Time-series analyses show that vegetation associations with large, long-lived species (conifers) appear to lag in response to climate variations until major fires (as seen in charcoal influx to sediments) reset the stage and encourage major vegetation reorganization. This provides evidence of the potential influence of catastrophic fire on the reorganization of ecosystems under periods of rapid climate variation and could have major implications for habitat and forestry.

Leaf Pores: An Important Link among Increasing Greenhouse Gases, the Water Cycle, and Rising Temperatures [13, 15]

Carbon dioxide and ozone (O₃), both greenhouse gases, directly affect plant physiological processes, including photosynthesis. These gases affect the opening and closing of microscopic pores (stomata) on plant leaves that regulate movement of water from the soil, through the plant, and into the atmosphere. Water vapor escaping through these pores cools the leaves and is important in the global water cycle. The number of stomata per unit of leaf area in grassland plant species in the southern United States was measured after the plants had been exposed for 4 years to a continuous CO₂ gradient spanning pre-industrial to near-double ambient concentrations. At higher CO₂ levels, stomatal density was greater for two species, decreased for one species, and unchanged for four species. In another field experiment using FACE technology, soybean plants were grown in the field at CO₂ and O₃ concentrations projected for the mid-21 st century to explore how these changes in atmospheric composition might affect a nationally important agroecosystem. This work has provided the first field-scale evidence that rising CO₂ and O₃ concentrations decrease the loss of water vapor through the stomata and have the potential to substantially reduce summer moisture supply to the atmosphere (at the same time conserving soil moisture) and cause a warming of vegetated surfaces that will raise surface temperatures independently of greenhouse warming.

U.S. Marine Resource Managers Seek Guidance from Climate Scientists on Impacts of Regime Shifts [11]

Mounting evidence indicates that decadal climate changes in ocean productivity must be considered in assessments of fish stocks. In 1998, marine resource managers perceived a climate regime shift in the North Pacific. This shift resulted in cooler ocean conditions within the California Current System and Gulf of Alaska, but warmer surface waters in the central North Pacific. These changes apparently led to increased biological productivity within much of the California Current System and Gulf of Alaska (e.g., increased abundance of plankton and recruitment of many commercial fish stocks including Pacific salmon species, Pacific hake, and groundfish in the California Current System, and Pacific salmon species, shrimp, pollock, Pacific cod, and sablefish in the Gulf of Alaska), but decreased productivity in the Central North Pacific (e.g., northward shift in the low chlorophyll surface waters and decreased survival of monk seal pups in the northern atolls of the northwestern Hawaiian Islands). In response to this, the U.S. National Marine Fisheries Service requested advice from the North Pacific Marine Science Association on the potential effects of climate change on fish stocks in the North Pacific. An ad hoc group of U.S. and international scientists was formed, confirmed that the North Pacific entered a new climate state in 1998, and detailed the associated changes. The group advised agencies to develop management policies with explicit decision rules and subsequent actions to be taken when there are preliminary indications that a regime shift has occurred. Existing indicators, such as temperature and primary production, make it possible to detect shifts soon after they occur, but due to limited understanding of the mechanisms that lead to regime shifts, it is not possible to reliably predict how long any new state will last. The report included four recommendations for incorporating regime shift concepts into fishery management activities: accept the regime concept for marine ecosystems; develop and maintain a comprehensive observational program to monitor changes; develop climate indices to aid ecosystem monitoring efforts; and make use of fish stock assessments to evaluate the vulnerability of ecosystems to various future regime scenarios.

New Long-Term Ecological Research Network Sites in Coastal Areas

The addition of the Moorea Coral Reef and the California Current Ecosystem to the Long-Term Ecological Research (LTER) Network has expanded the number of LTER sites to 26. These two new sites significantly augment the LTER Network, which had previously included only one marine site in the Antarctic, and ensure that high biodiversity and productivity ecosystems in most of the world's major biomes are represented in the network. Understanding gained from the site on the island of Moorea in the South Pacific will enable more accurate projections of how coral reef ecosystems respond to environmental change, whether human-induced or from natural cycles. The California Current System sustains active fisheries for a variety of finfish and shellfish, modulates weather patterns and the hydrologic cycle of much of the western United States, and plays a vital role in the economy of myriad coastal communities. Research will focus on how the influences of El Niño, the PDO, and multi-decadal warming trends affect these systems. The LTER program continues to have a major network-wide focus on climate change impacts on ecosystems.

Coral Reef Watch: Satellite Input [6, 20]

The number of reported coral reef bleaching events was minimal before the ENSO events of 1998 and 2002. During these events, significant coral mortality occurred throughout western Pacific and Caribbean coral reefs, bringing to light one likely correlation between anomalous temperatures and ecosystem response (Urban et al ., 2000). Since then, scientists have been developing an understanding of the potential causes and links leading to significant coral bleaching events. The Coral Reef Watch Program uses land- and satellite-based instruments and in situ tools for near-real-time and long-term monitoring, modeling, and reporting of physical environmental conditions of coral reef ecosystems. Biological, physical, and environmental data critical to coral reef ecosystems are continuously received, input into Coral Reef Watch, and provided to Reefbase, a global information system. These data are used to help design future marine protected areas, coral reef parks and refuges, and research areas (Heron and Skirving, 2004). Linking ecosystem models with current and past climate data will enable scientists to understand the relationship between climate parameters and coral ecosystem response. These efforts will provide tools that managers and stakeholders can use in the field to conserve corals. It is important to continue the acquisition of Landsat-like satellite data for these purposes.

Creation of the National Ecological Observatory Network

Work was initiated with the American Institute for Biological Sciences to set up a National Ecological Observatory Network (NEON) Design Consortium and Project Office. This consortium will develop a blueprint for the network and a plan for its implementation. NEON will be the first national observation system designed to answer ecological questions at regional and continental scales. Data from the network will help to develop a predictive understanding of the relationship between environmental change and biological processes. Focus areas for NEON include the impact of climate change on forests and agriculture, the emergence and spread of infectious diseases, the causes and consequences of invasive species, and the forecasting of biological change. For more information, see www.neoninc.org.