Experimental and Model Analysis of Large Disturbance Consequences for Forest Diversity

Duke University, Durham NC

Investigators

Abstract

9981392 Clark Understanding how forests respond to environmental change requires models that extrapolate from short-term observations to long-term dynamics. The current gap dynamic paradigm does this extrapolation under the assumption that recruitment is governed by conditions within canopy gaps 30 meters in diameter. Much empirical evidence and experimental tests of the paradigm suggest that diversity in many forests may depend on much larger canopy gaps than assumed in the models now used to forecast forest response to global change. If the underlying assumptions of the models are unrealistic, then predictions under novel environments of the future are likely misleading. In this project, a series of field experiments and model test will be conducted to test (1) gap sizes at which recruitment limitation is severe, and (2) whether maintenance of forest diversity depends on large gaps. Field studies will both test for specific life history stages at which recruitment limitation occurs and the factors responsible for limitation, while also providing parameter estimates for modeling studies. The extent to which fecundity, seed dispersal, predation in seed banks and availability of soil microbes affect recruitment in the closed forest understory and in gaps will be tested. Two modeling approaches will be used to determine the population and community consequences of experimental results. To determine the effects of demography observed in experimental and natural gaps on growth rates the PIs will use parameters in a stage structured population model. Analysis of the model will provide rate estimates implied by demography for each gap type and the contributions of each life history stage to population growth. An individual based model will be used to incorporate spatial elements, including seed dispersal and competition for light. Analysis of this model will provide estimates for the effects of gap size on forest diversity. Together, field experiments and modeling studies will allow the assessment of the contribution of disturbance to forest dynamics and thus, assessment of how forests may respond to novel environments in the future.