External Professor

My areas of research include causes and consequences of climate change with an emphasis on the study of climate-ecosystem feedback processes, theoretical ecology with an emphasis on elucidating relationships between community structure and functional integrity of ecosystems, causes and consequences of declining biodiversity, biogeochemical processes and their disruption, and the role of ecological integrity in human society.

Current Projects

The major project now underway is a study of ecosystem responses to climate change. At the Rocky Mountain Biological Laboratory in Colorado, my students and I are artificially warming a large area of a subalpine meadow with overhead electric heaters. We monitor changes in soil microclimate, vegetation phenology and community composition,arthropod diversity, carbon dioxide and methane exchange with the atmosphere, nitrogen cycling, and nutrient status of the soils and plants. Results to date indicate that a level of warming comparable to that expected from a doubling of atmospheric carbon dioxide exerts profound effects on soils and vegetation, and that these ecosystem effects will ultimately feed back on the climate. For example, the rate of carbon dioxide released from the system under the warming suggests that a significant positive feedback exists between montane ecosystems and the climate, with warming triggering an increase in this greenhouse gas. Observed warming-induced shifts in dominant vegetation from forbs to shrubs will likely also alter surface albedo and therefore the climate.

We have also begun an expansion of this project to the landscape scale, by creating a set of ecosystem manipulations along an elevational gradient in the Rockies. This will allow us both to generalize the insights derived from our original site to a larger area and to explore the relation between ecosystem response to natural climate variation along an elevational gradient with response to a manipulated climate at sites along the gradient. Because researchers elsewhere are attempting to derive information about ecological and biogeochemical response to climate warming by studying variation along natural gradients, our work provides a needed reality check on this surrogate procedure.

With a combination of modeling and field studies , we are also searching for useful "fingerprints" of climate change; indicators that will help determine if observed decadal trends in air temperature truly reflect a global warming phenomenon expected from buildup of atmospheric greenhouse gases. Potential candidates for such fingerprints are observed global trends in both seasonal phase and daytime versus nighttime values of air temperature. The field component of this work derives from our detailed 5 year data base on soil moisture and temperature responses to enhanced downward infrared radiation. The modeling work utilizes a one-dimensional energy balance model that has proven useful in understanding microclimate responses in our experimental plots.

In theoretical ecology, I have been studying the conse-quences for nutrient cycling of simultaneous mutualism and competition between plants and other organisms, and elucidation of microbial "strategies" of nitrogen allocation. My current interest is in the evolutionary implications of the plant-microbe relationship. I am also investigating implications of the species-area power-law relationship in ecology. Using the concept of self similarity, we have derived an endemics-area relationship, which improves our ability to estimate species loss under habitat destruction, a relationship between spatial turnover of species and the species-area exponent, which allows estimation of that exponent at large spatial scales, and a new probability distribution describing the spatial abundance distribution of species.