Wild ungulate impacts on ranchlands and across managed landscapes in the Hawaiian islands

Abstract

Invasive wild ungulates pose significant ecological and economic challenges worldwide, particularly in island ecosystems where the absence of large predators exacerbates their impacts. Across the Hawaiian Islands, wild ungulates such as axis deer (Axis axis), mouflon sheep (Ovis musimon), feral goats (Capra hircus), and wild pigs (Sus scrofa) contribute to overgrazing, habitat degradation, and impacts to agricultural production. While their effects on native ecosystems are well-documented, less is known about their influence on forage availability in ranchlands and how their distribution aligns with land management designations. This thesis examined the relationship between wild ungulate abundance, forage availability, and land-use classifications across the Hawaiian Islands. We investigated how wild ungulate presence affects forage loss and plant community composition using game cameras, exclusion cages, and vegetation surveys. Results indicate that while elevation is the primary driver of forage availability, wild ungulate detections were associated with reduced vegetation biomass at many sites, consistent with rancher concerns regarding overgrazing by wild ungulates. We analyzed predicted wild ungulate abundance across Priority Conservation Areas, Priority Hunting Areas, and Other Areas. Findings suggested that on the islands of Hawaiʻi and Maui, wild pigs and mouflon sheep are more abundant in conservation lands, while axis deer are more prevalent in agricultural and private lands, highlighting key areas for management intervention. These findings provide insights into the ecological impacts of wild ungulates on ranchlands and conservation areas, emphasizing the need for targeted, landscape-scale management strategies for invasive wild ungulates that achieve biodiversity conservation and sustainable agriculture goals.