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 2002:

Longer Growing Season Observed:

Data from the AVHRR satellite spanning two decades have confirmed that the growing season in the Northern Hemisphere above 40 degrees north latitude is getting longer, with spring ar riving earlier and fall somewhat later. Researchers using ground-based temperature records in tandem with satellite vegetation data found a tight linkage between changes in the growing season length of northern vegetation and year-to-year changes in temperature. The temperature component of this analysis came from the Global Historical Climate Network, which uses data from several thousand meteorological stations around the world. The satellite imagery was used to construct Normalized Difference Vegetation Indices (NDVIs), which serve as surrogates for plant growth. The findings indicated an increase since 1982 in the Eurasian growing season of nearly 18 days, while that in the U.S. increased by 12 days. Further research is needed to document fully the carbon cycle aspects of increased growing season length. However, the findings could potentially indicate enhanced carbon uptake in parts of the Northern Hemisphere.

Extensive Coral Bleaching Documented:

Reefs provide protection from erosion to coastlines and sand for beaches as well as harboring a tremendous diversity of animal and plant species. In 1998, extensive worldwide tropical reef coral bleaching was documented. The bleaching was triggered by high water temperatures related to the 1997-98 El Niño event. Coral bleaching occurs when coral colonies expel their symbiotic algae (zooxanthellae) under physiological stress, most commonly associated with high temperature and high input of solar radiation. Corals may recover from short periods of bleaching, but extended periods can be lethal. For example, the 1998 thermal anomaly lasted for about three months in Belize and induced mass mortality of corals throughout an area of 375 km2 in the south central lagoon of the Belizean Barrier Reef. Corals on the main outer barrier reef experienced some bleaching but mortality was minor compared to the catastrophic damage in the lagoon. The composition of the corals in extracted cores indicated that the magnitude of mass mortality during 1998 had not occurred in this area for at least 3,000 years. This record is a reason for concern that increased climatic variability and change (manifested most intensely during periods of warm variations) is leading to the degradation of coral reef ecosystems.

New Estimates of Insect Diversity:

The largest existing data set of tropical insects collected from identified plant species in the field was developed. The data set includes 75,000 records of 1,100 insect species hosted by 62 plant species. Analysis of the host specificity of these tropical herbivores showed that most leaf-chewing insects feed on several plant species, contrary to popular conceptions of high host specificity among tropical insects. The observation that these insect species apparently specialize on plant genera, rather than plant species or families, is of practical importance in understanding the impact of selective logging, range changes induced by climatic change, invasive species, and biological control. The observation also reduces estimates of global arthropod (insects and relatives) diversity from 31 million, based on plant species numbers, to 4-6 million arthropod species. This figure for arthropod diversity agrees with estimates based on taxonomic collections, reconciling an order of magnitude discrepancy between extrapolations of global arthropod diversity based on ecological samples of tropical plant communities and those based on sampling of regional faunas.

Model Evaluation and Improvement:

A rigorous evaluation of nine terrestrial ecosystem models was completed with the support of DOE, NASA, NSF, and the government of Canada. Models were compared to three years of field data collected on ecosystem water use, net primary production, gross primary production, net ecosystem production, and soil respiration in a boreal spruce forest. In this most extensive comparison of forest ecosystem models with independent field data conducted to date, it was discovered that more complex models tended to provide more accurate predictions of short-term (i.e., daily) water and carbon dioxide exchange rates, but not more accurate monthly and annual predictions. Several model improvements resulted from this work. This type of evaluation is required to understand the extent of remaining uncertainties and limitations of models used to predict the effects of global and regional environmental changes on the structure and functioning of terrestrial ecosystems.

Wetlands Sensitive to Global Change:

Results of several research studies have shown that both aquatic and marine wetlands are sensitive to increased sea level, higher frequency of wildfires, increased atmospheric CO2 concentration, and other factors. For example, a three-year study indicated that marsh burning temporarily increased plant root volume, thus increasing sediment elevation. Additional research evaluating effects of global and regional rates of sea-level rise and subsidence on coastal wetlands showed that some wetlands are able to "keep up" with sea-level rise by accumulating elevation through the production of roots and rhizomes, while other wetlands require inputs of mineral sediments via overland flow of sediment-laden water. In other research, species-specific differences in growth and productivity of coastal marsh plants in response to elevated CO2 observed in greenhouse experiments indicated potential changes in coastal marsh vegetation dominance in an elevated CO2 environment.