Invasive deer and goats cause major forage loss on Hawaii ranchlands, study finds

A new scientific assessment, the first to quantify the impact of wild ungulates on Hawaiʻi’s rangelands, reports that forage loss has occurred at roughly two‑thirds of the sites surveyed. The study, which examined grazing pressure from axis deer, mouflon sheep, feral goats, feral pigs and other introduced ungulates, identified axis deer as the predominant factor driving vegetation decline on ranches across Hawaiʻi Island and Maui. Researchers conducted systematic vegetation sampling and animal‑track surveys across a representative cross‑section of private and public grazing lands, documenting a consistent reduction in native grass and shrub cover where deer populations were highest.

The findings underscore growing concerns among ranchers and land managers about the sustainability of livestock production and ecosystem health in the islands’ upland pastures. Officials from the Hawaiʻi Department of Agriculture noted that the data provide a baseline for targeted management interventions, such as controlled hunts and fencing, aimed at mitigating deer‑induced degradation. As the study highlights the scale of ungulate‑related forage loss, it may shape future policy and conservation strategies intended to balance agricultural use with the preservation of native habitats.