University of Michigan
Department of Ecology and Evolutionary Biology

Richard Kobe, Chair and Professor, Department of Forestry, Michigan State University

Abstract
The composition and relative abundances of tree species in forest communities are fundamental attributes, but rarely have multiple processes causing these community-level patterns been considered together.  I will report on mechanisms that govern these community properties in wet tropical forest in Costa Rica as well as northern hardwood forest in northwestern lower Michigan. In wet tropical forest, seedling limitation does not constrain the recruitment of more common species. There also is little evidence to support that more common species are more susceptible to density dependent natural enemies. However, across species, there is strong covariance in seedling mortality responses to local conspecific density and shading, suggesting density-dependent natural enemies could exaggerate species differences in low-light seedling survival.  Nevertheless, species that survive poorly under low light and that are susceptible to density-dependence also are more growth responsive to soil nutrients (N, P, and base cations), even in the shaded understory. In Michigan northern hardwood forests, dramatic variation in species composition across glacial landforms can be explained by an interspecific trade-off between growth under high soil resources and survival under low soil resources. The species that survive well under low soil resources likely are excluded from higher fertility sites because of increasing competition for irradiance. Overall, these studies support that the multiple mechanisms governing forest community dynamics can be understood from the perspective of individual seedling / tree responses to resources and interactions with neighboring individuals.

Hosts: Inés Ibáñez and Annette Ostling

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