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Frederique Truchon

McGill University
Examining the impact of white-tailed deer (Odocoileus virginianus) browsing on white trillium (Trillium grandiflorum) in a protected old-growth forest.

Frédérique Truchon, Julia Nordlund, Virginie Millien

White-tailed deer (Odocoileus virginianus) populations have been on the rise across the majority of north-eastern America. Factors such as global changes in climate and decreased predation have facilitated their survival in areas at the northern end of their range, including in the Monteregian Hills region bordering Montreal. Once they establish or increase in abundance in an area, white-tailed deer can act as a keystone herbivore and have lasting effects on forest vegetation. To measure the impact of white-tailed deer browsing, 32 exclosures were set up at the Gault Nature Reserve on Mont Saint-Hilaire in 2006. We visited the exclosures and the associated control plots over the years to measure the abundance and size of white trillium (Trillium grandiflorum) – a spring-flowering plant often used as an indicator of deer browsing pressure. We found that the number and size of trillium were greater in exclosures than in areas subjected to browsing. Furthermore, our results show a decrease in the number of trillium over time, which suggests long-term impacts of white-tailed deer on the forest understory. We will expand on these results by getting density estimates and occurrence data on a fine geographical scale to examine the spatial use and impacts of the Gault Nature Reserve white-tailed deer population.