Deer browsing and light availability limit post oak (Quercus stellata) sapling growth and post-fire recovery in a xeric woodland

Abstract

Historically, oaks dominated the canopies of large regions of eastern North American forests, but at many sites current recruitment is insufficient to sustain oak dominance. Intense browsing by white-tailed deer (Odocoileus virginianus) and light limitation due to expansion by fire-intolerant tree species may cause poor oak recruitment. In a xeric woodland in Kansas USA, we used a deer exclusion experiment in natural canopy gaps to quantify effects of browsing and light availability on post oak (Quercus stellata) sapling performance, meaning growth and survival. Two weeks after beginning the experiment, a prescribed fire occurred that, due to natural burn heterogeneity, affected 29 of 31 experimental canopy gaps and top-killed 78.6% of experimental saplings. This allowed us to examine post-fire recovery in a sub-set of saplings. Our hypotheses were 1) ambient deer browsing intensity reduces post oak sapling performance, 2) sapling performance increases with gap size and light availability, 3) deer browsing effects on sapling performance vary with light availability, and 4) re-growth rate of saplings that were top-killed by fire is affected by light, deer browsing and the interaction of light and browsing. After five years, deer exclusion increased sapling growth in height and aboveground biomass. Sapling height growth was positively correlated with light. Deer effects on sapling performance generally were consistent across light environments. However, there was a weak pattern toward more negative effects of browsing in high light than in low light environments for saplings that re-sprouted post-fire. Protection from deer shortened the time required for saplings to re-attain their pre-fire height from five to three years. We conclude that deer browsing reduces post oak recruitment in canopy gaps in these xeric woodlands. Further, under current browsing intensity, fire return intervals less than five years will strongly limit oak recruitment.