The Currituck National Wildlife Refuge (CNWR) in North Carolina is inhabited by feral horses (Equus caballus), feral pigs (Sus scrofa), and white-tailed deer (Odocoileus virginianus). The impact of these species on the vegetation of CNWR is unknown. To assess impact, we created two replicate exclosure plots within maritime forests, brackish marshes, and maritime grasslands. An electric fence divided each habitat into two sections: including or excluding horses. On each side of the electric fence within each habitat, we sampled three different 5 × 5 m plots (i.e., 36 plots). The first was a fenced exclosure 3 m high, the second a fenced exclosure raised 1 m above the ground and extended to 3 m, and the third, a control, was not fenced. Within plots, we created two 1 m transects, and randomly selected and tagged grasses, forbs, shrubs, and trees. We measured the distances from base to tip of herbs and from branching point to terminal bud in shrubs. We used a linear model to analyze plant growth rate. We used a length ratio adjusted by the number of days as the response variable. Out of 1,105 tagged plants, we detected 87 disturbances; 80 where horses were present and 7 where horses were excluded. Overall, horses were responsible for 84% of disturbances. Most disturbances occurred in brackish marshes on Schoenoplectus pungens. We detected a significant effect of exclosure treatment on plant growth rate where horses were present (p = 0.035), but not where they were excluded (p = 0.32).
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Vol. 79 • No. 1