Effects of climate-driven species change on forest carbon and nitrogen cycling

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Most studies of the effects of climate change on forests have focused on the direct effects of predicted changes in temperature and precipitation. However, it is clear that in addition to the direct effects of climate on the functioning of forest ecosystems, there will also be indirect effects caused by climate-driven changes in tree species composition. As the climate warms, the ranges of North American tree species will gradually shift northward. At any given location, this will produce a change in tree species, favoring those species adapted to warmer climates. Because tree species are unique in many different ways, the change in species composition will alter the functioning of the forest ecosystem. This species change is not included in most computer models that predict the effects of climate change on forests. This study will fill that gap by linking two separate computer models with a statistical model that predicts how the ranges of tree species will shift as the climate changes, and a simulation model that predicts the effects of the species change on key aspects of forest function such as productivity, carbon storage, and nitrogen cycling. The linked models will be used to forecast the effects of climate change on forest functioning for several realistic scenarios of climate change over the next century. This initial effort is focused on the Northeastern U.S., but the approach and the models are potentially applicable to forests throughout the country, and even throughout the world, if sufficient information is available about the characteristics of the most important tree species. This project is a collaborative effort involving the Cary Institute of Ecosystem Studies and the USDA Forest Service.This research will have significant impacts on the scientific community studying climate change by focusing attention on the important, but often ignored, issue of how changes in tree species composition will affect the functioning and resillience of forests. In addition, this is clearly a policy-relevant question that is important for issues of forest growth, biodiversity, carbon sequestration, and retention of air pollution-derived nitrogen in forested watersheds in the Northeast. The principal investigators from the Cary Institute and the Forest Service will make the results of this research available and accessible to policy makers, natural resource managers, and the general public. The results of the study, including the technical details of the model results, will be available on web sites that will be maintained and supported by project staff. The models developed in this project will be useful for analysis of other important issues of global change, including tree species change caused by introductions of non-native insect pests and pathogens and by invasions of non-native plants. This project will also support educational opportunities for one postdoctoral associate and two undergraduate students.