The interacting effects of deer browsing and wind disturbance on forest regeneration
Krueger, Lisa Marie
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This dissertation explores the relationship between deer herbivory and wind disturbance in forest dynamics. Both herbivory and wind disturbances have individually been shown to dramatically alter the structure and composition of forest communities, but the interaction of these two factors has rarely been examined. Natural disturbances are common in most forests, and strong effects of large mammal browsing are a global phenomenon, so increasing our understanding of the interaction of these two factors is essential. I surveyed a wind-damaged old growth Pennsylvania forest to determine if Tsuga canadensis (hemlock) seedlings were protected by deer when growing on or near tip-up mounds, pits or downed tree trunks. The results showed that mounds continue to act as refugia from browsing 18 years after disturbance, but having multiple surrounding microsites did not reduce browsing levels. I also documented the community-level consequences of the interaction of deer herbivory with two important disturbance legacies; windthrow woody debris and recalcitrant herb understories. This study demonstrated that woody debris abundances had very little effect on deer browsing, whereas fern abundances had strong effects on the structure and composition of the herb and woody communities. Next, I examined how deer herbivory affected the relationship between seedling growth, survival and light availability. Deer browsing altered the species growth hierarchy and negated or weakened the positive relationship between growth and light availability for several species. Finally, I examined variation in seedling growth and browse presence/absence as it relates to light availability and the neighboring woody community. This experiment revealed that the woody community surrounding an individual seedling excluded from deer did not affect the focal plant’s growth rate whereas light availability had a significant effect on plant growth for four species. Furthermore, when deer were present, this study demonstrated no change in browsing frequency or intensity in relation to neighboring communities. I believe this research fills in much needed gaps in our knowledge of how deer browsing can influence forest community dynamics following wind disturbance. These studies will enhance our understanding of gap dynamics and subsequently help guide management decisions in wind disturbed forests.