Large swaths of the Eastern Deciduous Forest biome are suffering declines in biodiversity, particularly within species-rich understory layers. There is compelling evidence that these losses are caused in part by modification of historic disturbance regimes (e.g., extensive logging). In addition, the extirpation of apex predators and lax game management have led to widespread over-browsing, reducing biodiversity region-wide. However, the impact of over-browsing is likely dependent upon both natural and anthropogenic disturbances. How these major processes interact and drive forest regeneration is poorly known yet fundamental to understanding forest dynamics and diversity maintenance. Here we experimentally evaluate how a common anthropogenic disturbance (salvage logging), deer browsing, and a dense understory of plant competitors regulate forest reorganization following a large-scale blowdown in a mature hardwood forest. In 2012, a tornado created four large blowdowns (3-6 ha) in western Pennsylvania. We randomly selected half of each blowdown to be salvage logged and left the other half as unsalvaged controls. Nested within each half, we constructed eight deer exclosures and established eight control plots. We also removed understory competing vegetation in half of these plots. Five years after the tornado (summer 2017), we resurveyed the understory community in all 64 experimental plots.
Results/Conclusions
Salvage logging had the strongest impact on forest regeneration and created communities that were moderately distinct from unsalvaged areas. Specifically, indicator species analyses show that control plots were associated with Smilax tamnoides, Acer pensylvanicum, and Carya seedlings, whereas salvaged plots were associated with Polygonum virginianum, Rubus, and Crataegus. Salvage logging had negligible effects on species richness and species diversity, and our preliminary analyses suggest that deer browsing and the removal of understory competitors had only moderate impacts on forest regeneration. Overall, salvaging created habitats that contrasted sharply with unsalvaged areas and likely promoted species coexistence at larger spatial scales. Our results for understory layers match those published by Royo et al. (2016) in Ecology for patterns of woody species regeneration.