A general synthesis of how patterns of constraint and system scaling vary among ecosystems within different environmental regimes will be developed through mathematical modeling. The search will be organized around three objectives: (1) To synthesize existing data from a spectrum of ecosystems as represented by various LTER sites, in particular, the gradient of sites across the North American continent that includes the deciduous forest on the east through the Konza LTER site in the tall.grass prairie to the Central Plains LTER site in the short.grass prairie. This work will focus on the role of key environmental drivers (insolation, temperature, moisture, nutrients, and disturbance regimes) in structuring specific ecosystems. (2) To implement an integrated set of computerized simulators which are sufficiently general that they may be applied across this gradient. (3) To test model.generated hypotheses and predictions against independent data representing ecosystems that were not involved in the model development. The ecosystem.level phenomena of interest in this research imply spatial scales as typically connoted by the term"landscape" or larger, and decadal to centennial time scales. The emphasis on transitions between ecosystem types implies anextension to spatial scales that are at least regional, andultimately continental, in extent. Four models, which are already developed and well documented, will serve as the starting point for this research: (1) the CENTURY model of carbon and nutrient dynamics; (2) the MAGIC model of soil and water chemistry; (3) the FORET model of forest dynamics; and (4) the STEPPE model of succession in semiarid grasslands. A principal task in the research will be the development of appropriate interfaces between these models in the context of simulating the pattern in the continental scale gradient. The significance of this research is that it will help us to develop a modeling base in support of comparative ecosystem analysis among sites in the LTER network and the development of ecosystem theory. The research will also address the issue of how measurements made at small scales in space and time can be extrapolated. Both the development of theory and an understanding of issues of scale are essential to the development of sustainable management regimes for the Earth's ecosystems. Drs. Shugart, and Lauenroth are leaders in the field of ecological modeling. The institutional support available to them is superior.
