Patch type influences on regeneration in a western Pennsylvania, USA, catastrophic windthrow

Abstract

We investigated the influence of differing patch types on the germination, growth, and survival of two species of tree seedlings in a catastrophic, old‐growth forest windthrow. We documented environmental conditions, and experimentally introduced seeds, transplanted seedlings, and manipulated litter and herbivore access to determine the effects of patch types during initial forest regrowth. Among patch types defined by substrate condition and exposure, we found significant differential influence of patch type on germination of seeds of a common colonizer, Betulaalleghaniensis. Patch types that provided exposed mineral soil allowed greater germination than other patch types, regardless of light availability. Germination of Acerrubrum varied among patch types in a fashion similar to that of B. alleghaniensis, although differences among patch types were not significant. Litter can also be the basis of patch classification. Both type and amount of litter significantly influenced emergence of seedlings, with broad‐leaf litter (in amounts typical of intact forest) producing greater inhibition of emergence than amounts of conifer needles typical of intact forest. Survival and performance of fenced and unfenced Acerrubrum seedlings transplanted into different patch types reflected influences of both herbivory and competition with existing vegetation. Survival was lowest where the Acer seedlings were most apparent to mammalian herbivores. Growth of Acer seedlings was greater when they were protected from herbivory and free of competition from surrounding vegetation. These findings demonstrate that patch types offer different suitability as regeneration microsites during early tree life history stages. Because these patch types are common and easy to recognize, the differences in species’ responses may be sufficiently general to apply in other disturbances of this type. If general species responses to patch types can be combined with knowledge of propagule abundance and patch abundance, it could provide a basis for improved understanding of post‐disturbance regeneration, via patch influences.