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Ungulate Browsing Maintains Shrub Diversity in the Absence of Episodic Disturbance in Seasonally-Arid Conifer Forest



This is the publisher’s final pdf. The article was published by the Public Library of Science and is in the public domain.Ungulates exert a strong influence on the composition and diversity of vegetation communities. However, little is known\ud about how ungulate browsing pressure interacts with episodic disturbances such as fire and stand thinning. We assessed\ud shrub responses to variable browsing pressure by cattle and elk in fuels treated (mechanical removal of fuels followed by\ud prescribed burning) and non-fuels treated forest sites in northeastern Oregon, US. Seven treatment paddocks were\ud established at each site; three with cattle exclusion and low, moderate and high elk browsing pressure, three with elk\ud exclusion and low, moderate and high cattle browsing pressure, and one with both cattle and elk exclusion. The height,\ud cover and number of stems of each shrub species were recorded at multiple plots within each paddock at the time of\ud establishment and six years later. Changes in shrub species composition over the six year period were explored using\ud multivariate analyses. Generalized Linear Mixed Models were used to determine the effect of browsing pressure on the\ud change in shrub diversity and evenness. Vegetation composition in un-browsed paddocks changed more strongly and in\ud different trajectories than in browsed paddocks at sites that were not fuels treated. In fuels treated sites, changes in\ud composition were minimal for un-browsed paddocks. Shrub diversity and evenness decreased strongly in un-browsed\ud paddocks relative to paddocks with low, moderate and high browsing pressure at non-fuels treated sites, but not at fuels\ud treated sites. These results suggest that in the combined absence of fire, mechanical thinning and ungulate browsing, shrub\ud diversity is reduced due to increased dominance by certain shrub species which are otherwise suppressed by ungulates\ud and/or fuels removal. Accordingly, ungulate browsing, even at low intensities, can be used to suppress dominant shrub\ud species and maintain diversity in the absence of episodic disturbance events

Publisher: Public Library of Science
Year: 2014
DOI identifier: 10.1371/journal.pone.0086288
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Provided by: ScholarsArchive@OSU
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