Scale-Dependent Browsing Patterns on Canada Yew (Taxus canadensis) by White-Tailed Deer (Odocoileus virginianus)

Steve K Windels,David J Flaspohler

doi:10.1155/2013/276583

Steve K Windels, David J Flaspohler

Open Access

https://doi.org/10.1155/2013/276583

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Abstract

Canada yew (Taxus canadensis) is a clonal shrub that forms discrete patches and was formerly an important component of forest understories in much of northeastern North America. Following Euro-American settlement, Canada yew has been extirpated or reduced in abundance throughout much of its former range, particularly in the USA; winter browsing by white-tailed deer (Odocoileus virginianus) has been implicated as responsible for much of its decline. Little is known about the factors affecting deer browsing intensity on Canada yew. We examined factors related to browsing intensity on Canada yew across three spatial scales in 29 forest stands in Michigan, USA. Browsing intensity on stems was related principally to two factors acting simultaneously across multiple spatial scales. Browsing intensity was negatively related to amount of Canada yew at the scale of the forest stand and negatively related to distance from the edge of Canada yew patches, effectively creating refugia from browsing. The browsing patterns we observed suggest that yew exists in two alternate stable states: (1) as loose aggregations of small stems or (2) large, dense patches of large stems. The implications of changes in deer density or snow cover to the probability of local persistence of Canada yew are discussed.

Highlights

It is well accepted that large mammalian herbivores make foraging decisions based on interactions with resources across several spatial scales [1,2,3]
Canada yew has been extirpated or its abundance significantly reduced from most of its range in the US Several factors are often implicated in this decline, including the conversion of mid-to-late-successional mesic forest habitats to agriculture and short-rotation forestry and intense slash fires following the logging of primary forests
Results from our study suggest that intensity of deer browsing on Canada yew in the Lake Superior Watershed was affected by two factors operating independently at two spatial scales relevant to white-tailed deer

Summary

Introduction

It is well accepted that large mammalian herbivores make foraging decisions based on interactions with resources across several spatial scales [1,2,3]. Opportunities to better understand spatially dependent browsing patterns by ungulates emerge with Canada yew (Taxus canadensis), a declining species that is sensitive to browsing. Canada yew has been extirpated or its abundance significantly reduced from most of its range in the US Several factors are often implicated in this decline, including the conversion of mid-to-late-successional mesic forest habitats to agriculture and short-rotation forestry and intense slash fires following the logging of primary forests. Canada yew is considered one of the most highly preferred winter forage items for white-tailed deer (Odocoileus virginianus) [11, 12]; erupting populations of deer following the large-scale disturbances of the late 1800s and early 1900s are often implicated in the decline of yew [8, 11, 13, 14]. White-tailed deer densities are currently at least 2–4 times greater in the Great Lakes states than at the time of European settlement [15], and high deer abundance continues to remain one of the primary

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