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 some of the USGCRP's major accomplishments related to Biology and Biogeochemistry of Ecosystems during Fiscal Year 2000:

Research has documented significant changes in the growth and development of Ponderosa and Jeffrey pine in response to elevated ozone exposure and elevated nitrogen deposition. Above-ground biomass increases, while root biomass decreases with exposure to ozone and nitrogen, raising important questions about predisposing trees to drought-induced mortality and other stressors. The interaction of ozone and nitrogen pollution has significant implications for the storage of carbon in soils, forest-floor litter, and woody biomass.

A new assessment of fire risk from climate change uses results from Mapped Atmospheric-Plant-Soil System (MAPSS) vegetation distribution model simulations for seven future climate scenarios. The dynamic simulations indicate that climate change could lead to increased fire frequency over much of the western United States and, under scenarios that project the greatest warming, over many eastern U.S. forests.

Research results suggest that increasing atmospheric CO₂ levels could stimulate the growth of rangeland plant species because of the direct CO₂ fertilization effect and indirectly by reducing water stress by virtue of increased water-use efficiency of plants at elevated CO₂ levels. In rangelands where undesirable species such as mesquite occur or are introduced, however, elevated CO₂ also could cause a deleterious effect on rangeland plant species composition by increasing the growth and establishment of such species.