Title:  The Influence of Deer and Horse Herbivory on a Mid-Atlantic Barrier Island Ecosystem
Author(s): Mark Sturm – NPS Assateague Island National Seashore
Year: 2007
Abstract: Abstract: White-tailed deer (Odocoileus virginianus), sika deer (Cervus nippon) and feral horses (Equus caballus) inhabit Assateague Island, a 37 mile long undeveloped barrier island located along the Atlantic coast of Maryland and Virginia. The effects of these ungulate populations on Assateague’s terrestrial habitats are profound. Between 2003 -2005, island shrub and maritime forest communities were subjected to an exclosure experiment where treatments included exposure to horse and deer herbivory, exposure to deer herbivory - rest from horse herbivory and rest from all ungulate herbivory. Overall herbivory was found to be reducing plant species diversity and altering plant community composition. In response to deer herbivory Acer rubrum (saplings), Cirsium spp., Eupatorium hyssopifolium, Solidago sempervirens, Lechea maritima, Vitis rotundifolia, Rubus spp. and Carex spp. exhibited significantly lower abundances (á = 0.05) while Scirpus pungens significantly increased in abundance. Additionally, in response to deer herbivory the average height of Myrica spp. And Dichanthelium acuminatum significantly increased while that of Solidago sempervires significantly decreased. Other monitoring has revealed that deer and horse herbivory combined is reducing the survival and reproductive success of Amaranthus pumilus, a species that is federally listed as threatened. These plant taxa, along with others that exhibited responses specific to horse herbivory, are under consideration as indicator species that will be used during the development of an adaptive management program. This program will monitor the effects of each ungulate population and provide essential information for developing management strategies for these populations as well as the barrier island ecosystem.

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