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 2001:

 Field studies with controlled, elevated CO₂ levels indicated that growth stimulation of a few invasive plant species in the arid U.S. Southwest was stronger than growth stimulation in native species.  In a separate controlled-environment experiment, increased atmospheric CO₂ improved seedling survival of five species of woody plants during drought, with the beneficial effects greatest and most consistent for the two species considered the most drought-tolerant. These findings indicate that responses to rising atmospheric CO₂ are species-specific, which could result in shifts in the species composition of plant communities.

In an ozone (O₃) sensitive wheat variety grown in the absence of ozone stress, elevated CO₂ did not enhance yield compared to yield at ambient CO₂.  On the other hand, yield was enhanced by elevated CO₂, compared to yield at ambient CO₂, when the wheat was grown at elevated ozone concentrations.  The latter occurred because elevated CO₂ prevented the suppression of yield by O₃, and the yield was effectively the same as if there was no O₃ stress.  In another experiment, stimulation of tree growth resulting from elevated CO₂ was fully negated by elevated ozone. These findings highlight the uncertainties in projecting crop and forest productivity as CO₂ and climate change, because energy production from fossil fuel combustion causes an increase in both tropospheric CO₂ and ozone, and at comparable relative rates.

After eight years of experimental manipulation of precipitation received by a forest, growth of existing large trees was mostly unaffected by annual and summer precipitation increases, or by decreases of as much as 30 percent.  However, seedling and sapling mortality and nutrient cycling were affected. The discovery that large trees were relatively insensitive to chronic changes in precipitation may require revisions of many models used to predict effects of climatic change on forests.

Synthesis of results from the Boreal Ecosystem-Atmosphere Study (BOREAS) and other research programs in North American boreal and Arctic ecosystems have demonstrated that high-latitude ecosystems play a major role in the climate system. Average temperature and precipitation in these regions have increased, but changes in soil moisture remain uncertain.