Impact of white-tailed deer on northern white cedar recruitment beyond the browsing vulnerability zone: A broad-scale study

Abstract

By selectively feeding on the new vegetation from forest regeneration, cervids influence the abundance of understory species. This can lead to recruitment failure for the consumed species. The impact of cervids on regeneration is generally studied at fine scales, making it difficult to generalize about the species distribution scale for co-occurring cervid and tree species. This is especially problematic for species such as northern white cedar (Thuja occidentalis L.), which is susceptible to browsing and has been declining throughout much of its range. In our study, we aimed to determine the effect of the spatio-temporal variations in white-tailed deer (Odocoileus virginianus Zimmerman) abundance on northern white cedar recruitment over a broad spatial scale. We combined distinct forest and wildlife monitoring databases for two Canadian provinces, Québec and New Brunswick. We also surveyed cedar regeneration and deer browsing pressure in a subset of plots located in Québec. In both provinces, we detected a negative effect of deer abundance and deeryard proximity on the recruitment of cedar saplings. In Québec, local deer browsing pressure also had a negative effect on cedar seedling abundance. As deer browsing pressure can vary considerably over a short distance, we recommend the inclusion of browsing indicators in national forest surveys to precisely assess the impact of browsing on regeneration and recruitment. This would allow managers to identify areas that are highly vulnerable to browsing and adapt forest management accordingly to reduce browsing-induced regeneration failures.