My research is directed towards understanding the role of human disturbance on the structure and function of terrestrial ecosystems. Over the past several decades we have come to realize that there are very few places unaffected by human disturbance, and therefore ecological research needs to consider the potential role that past and present human influence has had on the patterns and processes that we study. The disturbances that I am interested in are not just the obvious ones, e.g. cutting trees or plowing soil, but also the more subtle influences, e.g. air pollution or changes in harvesting technologies. I study these human influences by looking at their impacts on nutrient cycles, plant community composition and ecosystem productivity. Such ecosystem level research is best accomplished in the frame work of broad long-term interdisciplinary research sites. As a result of my strong interest in such sites I have been actively involved in helping to establish an international long-term ecological research network.

My recent research has three major emphases: levels of historical disturbance at major ecological research sites in North and Central America with a continuing focus on the Hubbard Brook Experimental Forest; effects of disturbance (regional air pollution, wind and cutting) on a subtropical forest in Taiwan, and effects of climate change on ecosystem structure. The larger survey work has clearly demonstrated that even well established long-term research sites, i.e. Hubbard Brook Experimental Forest, Luquillo Experimental Forest and Jasper Ridge Biological Preserve, have complex disturbance histories that influence current biological processes. We are currently working to develop a more complete picture of these influences. In our research in Taiwan we have shown that at least 20-40% of the N and S in precipitation reaching a remote forest is derived off-island. Therefore, any effort to mitigate local air pollution sources will be of limited impact. Future work will focus more heavily on ecosystem impacts. My climate change work is currently focusing on looking at how we might be able to identify local impacts of climate change as well as the early signals of those changes.

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