| Canada yew (Taxus canadensis Marsh.) is an evergreen shrub native to forests of northeastern North America. Anecdotal accounts suggest that before Euro-American settlement Canada yew was a common plant across its range in many forest types. However, confusion persists about the historic role of Canada yew in eastern forests and other aspects of its autecology. Here, I synthesized available information on the ecology and management of Canada yew, with particular focus on its historic range and abundance and the impacts of browsing mammals. Several unique life history traits, including high shade tolerance and a dense clonal growth form, allowed it to become locally abundant or dominant in 5-20% of mainland forest stands in the northern parts of its range, and to reach extreme understory dominance on ungulate-free islands in the Great Lakes and coastal Canada. The species' range has declined significantly from its historic maximum as a result of a combination of several factors, including fire, intensive forest management, and clearing of land for agriculture and other development. Browsing by wild cervids, however, appears to be the most common and ubiquitous cause of its decline across its range. Canada yew appears incompatible with white-tailed deer (Odocoileus virginianus) and moose (Alces alces) except at low levels of animal abundance or in regions where sufficient snowfall protects stems. Increasing white-tailed deer populations and reduced snowfall as a result of climate change in eastern North America threaten to extirpate this species from additional parts of its range in the next century. Commercial harvest for this species for paclitaxel and other anti-cancer pharmaceuticals is another emerging threat. |
