B.S., A.M., Stanford University, 1972
Ph.D., Duke University, 1976
I am most interested in plant growth and nutrition, and in the role of plants in ecosystem element cycles. For many years I have focused my research on Alaskan tundra ecosystems, where low temperatures, low light intensities, low nutrient availability, and a short growing season all interact to limit plant growth. In this work we have compared and evaluated the relative importance of these limiting factors in different kinds of tundra, in different plant growth forms, and over a range of time and space scales. My current focus is on a series of long-term, whole-ecosystem experiments at Toolik Lake, Alaska. In these experiments we have been able to follow responses of the vegetation to treatments such as fertilizer addition, artificial shading, and increased air temperature for as long as 15 years. The results of these experiments are of general importance because they have shown how initial responses to a change of environment are often not sustained in the long-term, due mainly to changes in competitive interactions among species in the tundra community. Tundra ecosystems, with their low species diversity, small plant stature, and relatively fine-grained spatial heterogeniety are excellent model systems for the study of interaction between the physical, chemical, and biotic components of the environment in regulating plant growth and abundance. A second major component of my research is in the regulation of terrestrial carbon accumulation and exchanges of carbon with the atmosphere. Much of this work involves the use of computer simulation models, working at a range of scales from an experimental plot in Alaska to whole continents to the entire globe. More recently, Ed Rastetter and I have carried this work further, into the development of theoretical models of the interaction of multiple limiting factors in control of terrestrial stocks of soil and plant organic matter.