Vegetation and Feral Horse (Equus caballus) Dynamics of Shackleford Banks, North Carolina: A Comparative Analysis

Abstract

Shackleford Banks, North Carolina is a barrier island with a population of feral horses that are currently monitored by the National Park Service (NPS). The horse population has been maintained at a carrying capacity below 130 individuals to avoid problems with overgrazing on the island. Since the initial implementation of the management guidelines, the conditions of the island have changed and the forest landscape has increased. To understand how the progressions of the forest into the dune habitats and the emergence of forest in the swale habitats have affected horse behavior, I studied the vegetation and horses on Shackleford Banks. In the study, I measured characteristics of the vegetation on the island including the vegetation species, vegetation height, and vegetative state (green or brown). For the horse portion of the research, I followed 11 harems on the island examining horse behavior and acquiring coordinate locations for construction of the horses’ home ranges. Since 1962, there has been a 14% increase in the amount of forest habitat and approximately 20% of the former swale area is now characterized by forest habitat. As a result, the amount of swale landscape has decreased and the remaining swales are more densely surrounded than those in the past. Additionally, the abundance of Spartina patens, a species in the horses’ diets, is decreasing in the swales. The appearance of Eremochloa ophiuroides (centipede grass) in the swales is not able to nutritionally compensate for the loss in S. patens. In response, the current population of horses utilized the swales less often and decreased their grazing behavior in the more dense areas. By grazing in the dune and marsh habitats, the horses avoided the closed areas and seemed to be able to compensate for loss in nutritional content by grazing on protein-rich vegetation in the marshes and dunes.