Changes in Ecosystems
USGCRP Fiscal Year 2003 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

Ocean primary production decreased since the early 1980s:

Satellite and in situ chlorophyll records show that global ocean primary production has declined more than 6% since the early 1980s. Almost 70% of this decline occurred in the high latitudes. The North Atlantic and North Pacific Oceans experienced increases in sea surface temperature of 0.7 and 0.4ºC, respectively, over the time period of the study. However, decreases in primary production in the Antarctic basin were not associated with significant warming. Satellite data were blended with in situ data and used as inputs to a model that computed seasonal ocean primary productivity. The reduction in primary production may represent a reduced sink of carbon via the photosynthetic pathway in the high-latitude oceans. It is not clear whether the changes observed are part of a long-term trend or if they might be related to decadal-scale climate variations, such as the Pacific Decadal Variability or North Atlantic Oscillation/Northern Annular Mode. (See Figure 22)

Climate regime shifts in marine ecosystems:

Climate regime shifts on multidecadal timescales affect the productivity of marine and terrestrial systems, thus it is critical to be able to recognize and predict regime shifts to manage ecosystems. Research has produced a new understanding of the impact of regime shifts on ecosystem productivity and structure. In the North Pacific Ocean, the Pacific Decadal Variability changed from warm to cool phase in 1998 and was accompanied by immediate increases in plankton productivity and species composition, and significant increases in numbers of Pacific Northwest salmon and other commercially important fishes. In the North Atlantic Ocean, changes in quantities of zooplankton and fishes were observed, particularly in the Gulf of Maine, associated with a reversal in the North Atlantic Oscillation/Northern Annular Mode. Based on these new findings, indicators of ecological change are being developed for fisheries management and policymakers.

Observed impacts of climate change on plant and animal species:

Analyses based on a large number of studies of plants and animals across a wide range of natural systems worldwide have found that many species have shifted their geographic ranges or changed temperature-sensitive behaviors — such as migration, flowering, or egg-laying — in ways consistent with reacting to global warming. However, causal attribution of recent biological trends to climate change is complicated because non-climatic influences dominate local, short-term biological changes. Any underlying signal from climate change is likely to be revealed by analyses that seek systematic trends, over time and across many diverse species and geographic regions that are consistent with what would be predicted by scientific understanding of the physiological tolerances of species to temperature. "Meta-analyses" provide a way to re-analyze and combine results from various studies to determine whether there are underlying consistent shifts.

One such re-analysis, based on observations made in studies of more than 1,700 species, documented significant range shifts averaging 6.1 km per decade towards the poles (or meters per decade upward in altitude) over timescales ranging from 16 to 132 years. The re-analysis found mean advancement of spring events by 2.3 days per decade, over timescales ranging from 17 to 1,000 years. A total of 279 species showed temporal and spatial responses that may be associated with 20th century climate trends. Another re-analysis based on observations made in 143 studies revealed a consistent temperature-related shift, or 'fingerprint', in species ranging from molluscs to mammals and from grasses to trees. More than 80% of the species that showed changes were shifting in the direction expected on the basis of known physiological constraints of species. The balance of evidence from these studies suggests that impacts of global warming are discernible in animal and plant populations.

Natural resource management to offset greenhouse gas emissions:

To help meet the need for identifying how terrestrial ecosystems can be managed to mitigate and adapt to climate change, optimize carbon sequestration and reduce greenhouse gas emissions, a symposium was held to examine natural resource management opportunities for sequestering atmospheric CO₂ and reducing greenhouse gas emissions across multiple biomes. The scope of the symposium included forest, agriculture, range, boreal, desert, grassland, and wetland systems. Information presented included management options for increased storage of terrestrial carbon; monitoring information on current terrestrial carbon stocks; new and innovative technologies and methodologies for measuring and monitoring greenhouse gases in terrestrial ecosystems; economic projections for alternative carbon sequestration and emissions reduction practices in different terrestrial ecosystems; and policy implications of scientific carbon research findings.

Some results presented indicate that nitrous oxide (N ₂O) mitigation in cropping systems can be achieved with little or modest yield penalties by better adjusting nitrogen fertilizer additions to crop nitrogen needs. Other presentations described how, on fertile forest sites, or after fertilizer application, carbon sequestration in moderately long-lived carbon pools may be sustainably enhanced.

Effects of climate change on experimental forests:

Precipitation amounts and atmospheric composition affected experimental forests in separate field experiments. Full analysis of the first eight years of an experimental manipulation of precipitation on a deciduous forest ecosystem in Tennessee revealed that changes in precipitation amount affected nutrient cycling and mortality of young trees, but had little influence on large-tree wood or fine root growth, or on litter decomposition. In general, the forest was resilient to altered precipitation amount, but long-term changes in forest species composition could result from changes in hydrology. In another field experiment (in Wisconsin), the postulated stimulation of trembling aspen growth by several years of elevated atmospheric CO₂ concentration (related to fossil fuel use) was approximately offset by a concomitant increase in tropospheric ozone (O₃) concentration (also related to fossil fuel use). These ongoing experiments and related activities are supplying policymakers with empirical data needed to evaluate the potential effects of global change on important ecosystems.

Farmers and ranchers can expect increased atmospheric carbon dioxide to be a mixed blessing:

Increased growth and yield are well-known responses of crops to CO₂ enrichment. However, recent research shows that increased CO₂ also can have undesirable effects in agricultural systems. When plots of shortgrass prairie in northeastern Colorado were exposed to twice-ambient CO₂ levels in open-top chambers, the forage produced had less nitrogen and was less digestable than forage produced in ambient-level CO₂. In another experiment, increased CO₂ stimulated the growth of five of the most important species of invasive weeds, more than any other plant species yet studied. This suggests that some weeds could become bigger problems as CO₂ increases. In other studies, at twice the ambient CO₂ level, white clover leaf area consumed by an insect pest (the Western flower thrips) was approximately 90% greater than leaf area consumed in ambient CO₂. Although enriched atmospheric CO₂ could provide some benefits to plants, farmers and ranchers may face some surprises in managing agricultural systems to sustain both yield and quality as CO₂ levels continue to increase.

Interagency Ecosystem Model-Data Comparison:

A multi-agency effort to evaluate 13 stand-level forest ecosystems models, which varied in spatial, mechanistic, and temporal complexity, was carried out with the use of independent field data. The field data were obtained from eastern Tennessee over an 8-year period using a wide range of methods. No single model consistently performed the best at all time steps or for all variables considered. Inter-model comparisons showed good agreement for water cycle fluxes but considerable disagreement among models for predicted carbon fluxes. The mean of all model outputs was nearly always the best fit to the observations. Models missing key forest components or processes, such as roots or modeled soil water content, were unable to provide accurate predictions of ecosystem responses to short-term drought. Models using hourly time steps, detailed mechanistic processes, and having a realistic spatial representation of the forest ecosystem provided better predictions of observed data. Predictive ability of all models deteriorated under drought conditions, indicating that further research is needed to evaluate and improve ecosystem model performance under unusual conditions, such as drought, that are a common focus of environmental change discussions.