ASSESSMENT OF THE EFFECTS OF FERAL HORSES, SIKA DEER AND WHITE-TAILED DEER
ON
ASSATEAGUE ISLAND'S
FOREST AND SHRUB HABITATS

Assateague Island National Seashore
Final Report
May 2007

By
Mark Sturm
Ecologist
Division of Resource Management

Assateague Island National Seashore
7206 National Seashore Lane
Berlin, MD 21811
(410) 641-1443

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Abstract

Native white-tailed deer (Odocoileus virginianus) and non-native sika deer (Cervus nippon) inhabit Assateague Island National Seashore (ASIS) along with feral horses (Equus caballus). During the fall of 2002 four forest and four shrub study sites were established in order to monitor the impacts of deer and horse herbivory within these< habitats. Each study site included three treatments: a horse and deer exclosure (Total), a horse only exclosure (Partial) and a Control treatment where both deer and horses were allowed to forage. Between 2003 and 2005 pin-contact, cover-board and deer browse data were collected at each study site. Additionally, both deer populations were estimated each winter (2003-2006), post hunting season, using distance-sampling. During this research, existing levels of ungulate herbivory were shown to significantly reduce species richness, evenness and diversity in maritime forest habitats as well as to alter the vegetative community composition in both habitats. In addition, many plant taxa responded significantly to project treatments through changes in their abundance or mean height. These responses were frequently directly attributable to either deer or horse herbivory, or the combined affect of both groups. This information will be used in conjunction with that provided by other ongoing research, investigating deer movements and habitat utilization, to develop monitoring protocols designed to reflect the status and trends of ASIS deer populations, as well as to quantify the vegetative effects of existing levels of herbivory. Ultimately, these vegetation monitoring protocols will form part of an adaptive management program that will help ASIS make informed decisions regarding the management of Assateague Island’s terrestrial flora and fauna communities.

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