Deer density affects ground-layer vegetation differently in conifer plantations and hardwood forests on the Boso Peninsula, Japan |
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Authors: | Maki Suzuki Tadashi Miyashita Hajime Kabaya Keiji Ochiai Masahiko Asada Takeshi Tange |
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Institution: | (1) Graduate School of Agriculture and Life Sciences, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657, Japan;(2) NPO Boso Wildlife Research Party, Sasa 1643, Kimitsu Chiba, 292-0526, Japan;(3) Natural History Museum and Institute, Chiba, Aoba 995-2, Chuo-ku Chiba, 260-8682, Japan;(4) The Tokyo University Forest in Chiba, Amatsu 770, Kamogawa Chiba, 229-5503, Japan |
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Abstract: | Deer overabundance reduces forest ground-layer vegetation and can cause cascading impacts on a forest ecosystem. To predict
these effects, we must elucidate the relationship between deer density and the status of ground-layer vegetation. This relationship
was studied in the Boso Peninsula, where the deer population density exhibits a clear geographical gradient. We examined species
richness and cover of ground-layer vegetation at several cedar plantations and hardwood forests in the Boso Peninsula. We
also examined whether deer impacts were altered by light condition, soil water content and forest type (cedar and hardwood).
Species richness of ground-layer vegetation was maximized at an intermediate level of deer density, suggesting an intermediate
disturbance effect. This phenomenon was compatible with the observation that evergreen species, which were competitive dominants,
decreased with increasing deer density, whereas less competitive deciduous species increased until herbivory was intermediate.
As deer density increased, cover of ground-layer vegetation gradually decreased, but species unpalatable to deer increased
in abundance, suggesting indirect positive effects of deer for unpalatable species. Cedar plantations tended to have greater
species richness and ground-layer cover than hardwood forests with similar deer levels. Canopy openness, an indicator of light
conditions, increased species richness of hardwood forests and ground-layer cover of cedar plantations, even under deer herbivory.
Topographic wetness index, an indicator of soil water content, significantly increased the ground-layer cover of cedar plantations
under deer herbivory. These results emphasize the importance of environmental productivity and forest type in the management
of ground-layer vegetation experiencing deer overabundance. |
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Keywords: | Deer overabundance Intermediate disturbance hypothesis Indirect positive effect |
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