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Seminar Abstract

Don McKenzie - October 29, 2002


Climatic and biophysical controls on conifer species distributions in mountains of Washington State, USA.

Don McKenzie, David W. Peterson, David L. Peterson, Peter E. Thornton

The effects of climatic change on vegetation may be particularly strong in mountains, but climatic influences are difficult to assess, because complex topography produces sharp gradients in the biophysical environment. However, with the increasing availability of climatic data at finer spatial resolution and the development of topographically sensitive hydrological models, it is becoming possible to develop quantitative models relating species distributions to climatic and biophysical variables. We quantified associations between climatic and biophysical variables and individual conifer species distributions in mountain forests at three spatial scales, using generalized linear models. We compared simple climatic variables (annual temperature, growing-degree days, annual and seasonal precipitation) to biophysical variables (soil, hydrologic, and solar radiation) derived from climatic variables. For the majority of species, we were able to fit variables representing both moisture and temperature gradients, and in all but a few cases these models identified a unimodal response of species occurrence to these gradients. In some cases the ecological/environmental niche of a species had been clearly captured by the model, whereas in others a longer gradient in the predictor variable(s) would be needed. Responses of most species were consistent across three spatial scales. By identifying the ecological niches of multiple species, we can forecast their redistribution on the landscape in response to climatic change, evaluate the predictions of simulation models, and alert managers to particularly sensitive or vulnerable ecosystems and landscapes.

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