Deer Eat Away 24% of Hawaiʻi's Ranchland Forage

Invasive deer and goats are causing significant forage losses on Hawaiʻi's ranchlands, with axis deer being the primary driver of decline. A study by the University of Hawaiʻi at Mānoa's College of Tropical Agriculture and Human Resources found that forage losses were detected at two-thirds of sites surveyed.

The study, which surveyed 35 sites, found that axis deer were detected at 95% of surveyed sites on Maui. There are roughly 47,000 deer ranging across a third of Maui at elevations up to 2,150 meters (7,050 feet). Sites dominated by axis deer produced about 24% less forage on average than ungulate-free sites.

Non-native ungulates, including axis deer, were largely introduced to Hawaiʻi between the 1700s and 1960s. The study's findings provide the first evidence that grazing by wild ungulates, particularly invasive axis deer, is reducing forage at Hawaiʻi's working cattle ranches.

## Why it matters The significant forage losses caused by invasive deer and goats have important implications for Hawaiʻi's ranchlands. The study's lead researcher noted that the losses are significant, and the findings match what ranchers have been reporting for years. The presence of invasive species, including fireweed, which was found at nearly 70% of sites, further exacerbates the issue.

The study was published in Rangeland Ecology & Management and provides valuable insights into the impact of invasive species on Hawaiʻi's rangelands. The research was led by the University of Hawaiʻi at Mānoa's College of Tropical Agriculture and Human Resilience (CTAHR), and the findings have important implications for the management of Hawaiʻi's ranchlands.