Effects of Deer Browsing on Nutrient Cycling and Regeneration Dynamics in a Carolinian Old-Growth Forest of Ontario

Old growth forests are increasingly rare but important carbon sinks which harbour rich biodiversity. Chronic browsing by the white-tailed deer (Odocoileus virginianus) is a major problem in northern temperate forests where deer numbers have increased in recent decades driven by stricter hunting rules and reduced predation necessitating local monitoring of vegetation responses. The objective of this study was to determine the effects of deer exclusion on tree regeneration dynamics and soil nutrient cycling in an old growth Carolinian forest. This was done using exclusion fencing and tip-up mounds at McMaster Forest Nature Preserve and the Sheelah Dunn Dooley Nature Sanctuary in Hamilton Ontario. Tree regeneration was surveyed from thirty 1m x 1m quadrats within exclusion plots and another thirty quadrats from deer browsed areas adjacent to the exclusion plots. Soil samples were taken from each quadrat to analyze browsing impacts on nitrate, phosphate and soil organic matter. Red oak (Quercus rubra) was planted at the top and base of tip-up mounds of varying heights and widths and monitored for deer access and browsing activity. Results show a significantly higher density of woody plants within exclosures compared to non-exclosures (p=0.0089) and twice more abundance of highly palatable species within the exclosures. However, species richness (p > 0.05) and diversity (p > 0.05) were minimally impacted by deer browsing showing a resilient old growth forest. Soil nitrate was consistently higher in the non-exclosures while phosphate was consistently higher within deer exclosures. Finally, more seedlings survived at the top of mounds than the bases showing the potential of tip-up mounds to be a natural method of deer exclusion and a critical avenue for restoring over-browsed forests.