Collaborative Research: Influences of Geology and Tree Species Composition on the Response of Forest Nutrient Dynamics to an Exotic Pest

During the last century forests in the eastern U.S. have been subject to a continuing series of invasions by exotic pests and pathogens. While we know much about the biology and the mode of action of many of the pests, there has been little research on the ecosystem-level consequences of these invasions. Because these pests and pathogens usually target specific tree species, their long-term effect is often a change is species composition of the forest, which can lead to changes in productivity, carbon and nitrogen sequestration, and nutrient cycling. This project will examine the response of northeastern U.S. forests to the beech bark disease (BBD), an introduced disease complex involving a scale insect and a pathogenic fungus. The BBD has killed or reduced the vigor of American beech trees throughout the Northeast. Our observations and previous studies suggest that in some places beech can maintain its dominance in the forest despite the disease, while in other places it is being replaced by competitors, especially sugar maple. A shift in forest species composition could engender numerous changes in forest function, including carbon storage and nitrogen retention, largely caused by the differences in litter quality between species. Sugar maple, in particular has unique qualities of carbon and nitrogen cycling. Because sugar maples compete better on soils of moderate to high base status, and the base status is largely determined by the underlying geology of the forest, the principal hypotheses in this project are that (1) geologic substrate will strongly influence the response of the tree community to BBD, and (2) the changes in tree community composition will have a significant effect on the carbon and nitrogen dynamics of the forest ecosystem. We will test these hypotheses using a combination of field surveys and intensive plot studies in the Catskill Mountains of New York and the White Mountains of New Hampshire. We will extrapolate our knowledge to longer time frames by developing a simulation model of the effects of species change on carbon and nitrogen dynamics. We will also use a field experiment to help us understand how species and Ca availability interact in regulating litter decomposition. This research is a collaborative effort of investigators at the Institute of Ecosystem Studies, the University of Kentucky, and the University of Illinois.