It has been suggested that cervid herbivores may critically determine species composition of forest vegetation through the promotion of browse tolerant and browse resistant shrubs and trees in early successional stages. The idea is that such plant species may continue to benefit from a priority effect, as they may inhibit growth of browse sensitive species through shading and possibly nutrient competition. Hence, the presence or absence of herbivory may lead to alternative equilibria in tree species composition.
We tested this idea on Anticosti Island, Québec, Canada. The island is ideal for such studies as it exhibits unusually high densities of white-tailed deer (Odocoileus virginianus). Exclosures were established in forest cutblocks shortly after all mature trees had been harvested (t0). After eight years (t1), new exclosures were established, protecting previously accessible plots from deer herbivory. We monitored vegetation composition in all three treatments until five years after establishment of the second exclosure treatment (t2).
Results/Conclusions
Despite dominance of browse resistant species in control plots after eight years (t1), there was a remarkable recovery of nearly all browse sensitive shrubs and tree seedlings after five years of protection of plots previously open to herbivores (t2). Although prolonged browsing may critically affect plant species composition in boreal forests we suggest that resilience of plant communities to herbivory may be higher than previously thought.