Effects of white-tailed deer on Tsuga canadensis regeneration: evidence of microsites as refugia from browsing

Both herbivory and windthrow disturbances have individually been shown to dramatically alter the structure and composition of forest communities; however, the interaction of these two factors has scarcely been examined. Windthrow disturbance creates microsites such as fallen logs and treefall mounds and pits that may hinder movement and limit visibility of large mammals, thereby reducing the impact of browsing by white-tailed deer. In an old growth Pennsylvania forest that was severely wind-damaged in 1985, a previous study based on sampling in 1994 demonstrated reduced browsing and greater Tsuga canadensis (L.) Carr seedling density on treefall mounds (Long et al., 1998). In this study we surveyed mounds to see if they continue to be effective browsing refugia 9 y later. We also determined whether other types of microsites and nearby microsites provide protection from browsing and tested for an associational density refuge, whereby seedlings of a preferred species are less browsed when surrounded by a high density of saplings. Tsuga canadensis seedlings occurred more frequently on microsites, particularly logs and mounds, whereas randomly selected points occurred most frequently off microsites. Tsuga canadensis seedlings that established off microsites were more heavily browsed than seedlings on mounds or logs. Seedling heights were greatest on mounds and shortest on logs. Although growing on a microsite acted as refugia from browsing, having multiple surrounding microsites did not. Additionally, seedling browse damage was not decreased by having multiple nearby saplings, suggesting no associational defense. Nevertheless, certain microsites continue to provide refugia from browsing 18 y after disturbance and, thereby, enhance regeneration of Tsuga canadensis.