{"id":240911,"date":"2026-09-21T09:00:43","date_gmt":"2026-09-21T19:00:43","guid":{"rendered":"https:\/\/www.hawaii.edu\/news\/?p=240911"},"modified":"2026-09-21T09:51:48","modified_gmt":"2026-09-21T19:51:48","slug":"invasive-deer-ranchlands","status":"publish","type":"post","link":"https:\/\/www.hawaii.edu\/news\/2026\/09\/21\/invasive-deer-ranchlands\/","title":{"rendered":"Invasive deer, goats are eating away Hawaiʻi\u2019s ranchlands"},"content":{"rendered":"Reading time: <\/span> 2<\/span> minutes<\/span><\/span>
\"sheep\"
(Photo credit: Melissa Price)<\/figcaption><\/figure>\n

The first study to measure wild ungulate (axis deer, mouflon sheep, goats, pigs, etc.) grazing on Hawaiʻi<\/span> rangelands finds forage losses at two-thirds of sites surveyed, with axis deer the clearest driver of decline across ranches on Hawaiʻi<\/span> Island and Maui.<\/p>\n

Led by researchers at the University of Hawaiʻi<\/span> at Mānoa\u2019s<\/span> College of Tropical Agriculture and Human Resilience (CTAHR<\/abbr>), the research provides the first evidence that grazing by wild ungulates, particularly invasive axis deer, is reducing the forage at Hawaiʻi’s<\/span> working cattle ranches. Published in Rangeland Ecology & Management<\/em>, the study documented forage losses at 66% of 35 sites surveyed<\/a>.<\/p>\n

“This is the first study to actually measure how much forage wild ungulates are removing from working ranchlands in Hawaiʻi,<\/span> and the losses are significant,” said Professor Melissa Price, corresponding author and researcher at CTAHR<\/abbr>\u2019s Department of Natural Resources and Environmental Management (NREM<\/abbr>).<\/p>\n

Measuring forage loss<\/h2>\n
\"deer\"
(Photo credit: Melissa Price)<\/figcaption><\/figure>\n

Non-native ungulates were largely introduced between the 1700s and 1960s. On Maui, axis deer were detected at 95% of surveyed sites, with roughly 47,000 deer ranging across a third of the island at elevations up to 2,150 meters.<\/p>\n

“Axis deer came out as the biggest driver of declining rangeland condition, which matches what ranchers have been telling us for years,” said CTAHR<\/abbr> Extension agent Mark Thorne, a study co-author and rangeland specialist.<\/p>\n

The team compared vegetation growth with and without ungulates using motion-triggered trail cameras alongside fenced exclusion plots. Sites dominated by axis deer produced about 24% less forage on average than ungulate-free sites. Feral goats showed similar impacts. However, wild pigs and mouflon sheep frequented higher-elevation areas with generally faster forage production, illustrating how species-specific habits complicate land management.<\/p>\n

Slow recovery<\/h2>\n
\"cattle\"
(Photo credit: Melissa Price)<\/figcaption><\/figure>\n

Several Maui sites sat within areas burned by the August 2023 wildfires. Researchers warned that overgrazed rangelands recover more slowly after fire and stay vulnerable to fire-prone weeds such as fireweed, found at nearly 70% of sites.<\/p>\n

“We’ve had to shrink our herds some years because there just isn’t enough grass left once the deer get to it,” said Greg Friel, a Maui island cattle rancher and co-author on the study. “It’s good to finally see numbers behind something ranching families here have been living with for a long time.”<\/p>\n

The study was funded by the United States Department of Agriculture (USDA<\/abbr>) Western Sustainable Agriculture Research and Education (SARE<\/abbr>) program and led by Lauren Katayama, who recently earned a master\u2019s degree from NREM<\/abbr>.<\/p>\n","protected":false},"excerpt":{"rendered":"

Hawaiʻi<\/span> rangelands finds forage losses at two-thirds of sites surveyed, with axis deer the clearest driver of decline across ranches on Hawaiʻi<\/span> Island and Maui.<\/p>\n","protected":false},"author":16,"featured_media":240920,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[30],"tags":[222,212,665,899,1363,1314,544,1600,158,73,9],"class_list":["post-240911","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-research","tag-agriculture","tag-college-of-tropical-agriculture-and-human-resilience","tag-conservation","tag-ecology","tag-manoa-research","tag-manoa-sustainability","tag-natural-resources-and-environmental-management","tag-public-impact-research","tag-publication","tag-sustainability","tag-uh-manoa","entry","has-media"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t