9411972 Tilman The Cedar Creek Natural History Area is important because of its location on the climatically and edaphically controlled boundary between prairie and forest. This "tension zone" between forest and prairies is highly sensitive to climatic variation and strongly impacted by edaphic factors, especially soil nitrogen availability fire frequency and by herbivores and predators. The dominant vegetation of the region, oak savanna, itself has unusually high species richness because its flora and fauna include both prairies and forest species. It is the diversity and dynamics of these ecosystems that form the focus of their research. Three major questions guide their research: (1) What factors, interactions and positive and negative feedback effects control the species composition and species dynamics of our successional grasslands and native savanna ecosystems? (2) What forces determine how many species can persist on various trophic levels within our ecosystems, i.e., what controls biodiversity? (3) What are the impacts of species composition and biodiversity on the functioning of these ecosystems? Succession and biodiversity are tightly linked. They are interested in succession because it is the process of ecosystem assembly. Disturbances often cause the local loss of species. The factors that drive the successional processes, are thus the processes that control and maintain diversity. They have performed numerous long-term experiments that have provided insights into the impacts of biodiversity on the stability and functioning of these ecosystems. They will continue to seek the underlying mechanisms that cause broad scale patterns in ecosystem composition, diversity, and productivity in their successional grasslands and prairie openings, and will expand their efforts in oak savannas. Their ongoing studies will further quantify the effects of biodiversity on ecosystem resistance to and resilience from climatic variability. Their new biodiversity e xperiment should provide some of the first direct field evidence of the effects of species and functional diversity on numerous aspects of population and ecosystem stability and functioning.
