Our long-term studies at Cedar Creek, which were begun in 1982 with the funding of our LTER proposal by the National Science Foundation, are focused on six major issues and questions. These six foci explore topics of fundamental scientific interest and of relevance to human-driven global environmental change, especially the impacts of elevated nitrogen deposition, of increased concentrations of atmospheric carbon dioxide, and of the loss of biodiversity on ecosystem functioning. In addition, we have performed other shorter-term related studies. These studies are supported by grants from the National Science Foundation, Department of Energy, the Andrew Mellon Foundation, and other sources. The Cedar Creek LTER combines long-term experimentation and observation to examine the controls of successional dynamics and spatial patterning in ecosystems at the prairie-forest boundary. The LTER project has established more than 1100 permanent, long-term experimental plots as well as 2300 permanent observational plots distributed across a chronosequence of 22 old fields. Our studies focus on hypotheses concerning the direct, indirect and feedback effects of various species and ecosystem elements on each other. Although we study whole ecosystem processes, a major goal of our project is to understand the underlying mechanisms that control these processes. Work focuses on:
Our studies of the mechanisms of plant competition, done by David Tilman and David Wedin, use results from over 900 plots in a long-term experimental garden in which we are growing many major grassland species in monocultures and in various pairwise combinations. These plots were established on an experimental soil nitrogen gradient. We routinely monitor soil nitrate and ammonium concentrations, as well as plant biomass and allocation patterns, in these plots. Our studies of soil carbon and nitrogen dynamics, which involve David Grigal, John Pastor, Don Zak, Peter Homann, David Tilman, David Wedin and Jean-Alex Molina, include work on litter decomposition, species-specific litter feedback effects, N mineralization, nitrification and leaching, N fixation, microbial and mycorrhizal biomass, and dissolved organic carbon dynamics. Studies of primary productivity and the controls of plant community involve Scott Wilson, Martha Phillips, Richard Inouye, Mark Davis, Nancy Huntly, Tania Vincent and Mark McGinley. This research includes nutrient addition experiments in uplands and wetlands, water table manipulations in wetlands, detailed studies of the nutrient and light dependence of growth of major plant species, studies of the role of soil heterogeneity and of plant colonization, growth and competition in patchy habitat. Herbivory research, led by Nancy Huntly, Richard Inouye, Mark Ritchie, John Pastor, and David Tilman, includes long-term observations on the population dynamics of the major herbivores (small mammals, deer, and grasshoppers), selective removal of herbivore guilds, deer exclosure experiments, gopher exclosure experiments, comparisons of fenced and unfenced nitrogen gradients, studies of the impact of herbivores on carbon and nitrogen dynamics and cycling, and studies of replicated monoculture and competition plots in our experimental garden that either do or do not have one or more grasshopper species. Our studies of disturbance, coordinated by Scott Wilson, David Tilman, Eville Gorham, John Tester, and Richard Inouye, consist of comparisons of disturbed and undisturbed plots that receive different rates of nitrogen addition, our 29-year running set of prescribed burns in oak savanna, a 6-year running set of prescribed burns in an old field, manipulations of depth to water table (as a mimic of effects of climatic change), and observations on the pattern and frequency of disturbances in old fields, savanna, forest, and wetlands. We are also working on analytical and simulation models of various ecosystem attributes. These models, which address processes occurring on a range of spatial and temporal scales, are being developed and tested under the direction of David Tilman, John Pastor, and others.