Print PageBrowsing by mammalian herbivores like white-tailed deer is known to dramatically alter species composition in the forest understory, but it is not known how long effects of deer density persist after overabundant populations decrease to more sustainable levels. We investigated this question using data from a 30-year study wherein deer density was manipulated experimentally for the first 10 yr (1979-1990) in northwest Pennsylvania. Ten-year average deer density ranged from 3.6 to 28.0 deer/km2 in 16 experimental stands across four study sites. Enclosures were removed in 1990 and plots have experienced roughly equivalent, ambient deer densities since then. In summer 2010, we sampled understory vegetation in 12-20 1-m2 quadrats per stand. We estimated percent cover of major plant taxa (ferns, grasses, forbs, etc.) and counted number of morphospecies per plot.
Results/Conclusions
Deer density during stand initiation (1979-1990) has lasting impacts on the forest understory in 30-yr-old forests (2010). Increasing deer density caused significant (P = <0.05) long-term legacies in the form of increased percent cover of ferns, decreased percent cover of seedlings/saplings and of forbs, and decreased plant species richness in the understory. Though similar effects have been reported in shorter-term studies and in long-term exclosure studies, these are the first such results for a long-term experiment where deer density was manipulated across a critical range of densities. Because white-tailed deer are overabundant across much of their range, these results provide critical insight into how long the legacy of these overabundant populations can persist even after populations are reduced.
