Invasive Deer Have Reduced Hawaii Ranchland Forage
A study links non-native ungulate populations to a significant decrease in available grazing biomass across Maui.
Updated on Sept. 27, 2026 in Botany
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University of Hawaiʻi at Mānoa researchers documented forage losses at two-thirds of surveyed ranchlands across the state. The study indicates that axis deer are a primary driver of this ecological impact, particularly on the island of Maui.
Why it matters
The presence of non-native ungulates introduced between the 1700s and 1960s is altering vegetation productivity and landscape health. These findings highlight the competitive pressure these animals place on local agricultural and native ecosystems.
Data collected from 35 sites showed that axis deer, which number roughly 47,000 on Maui, correlate with a 25% decrease in forage yield. Additionally, 70% of surveyed sites were found to contain fireweed.
The players
University of Hawaiʻi at Mānoa
A public research university leading studies on Pacific island ecology and agricultural sustainability.
U.S. Department of Agriculture
A federal executive department responsible for developing and executing laws related to farming, forestry, and food.
The details
Researchers at the University of Hawaiʻi at Mānoa utilized motion-triggered trail cameras to monitor vegetation growth across 35 sites. By comparing growth patterns at locations with and without non-native hoofed animals, the team quantified the impact of grazing pressure. The study also noted that fireweed—a toxic, invasive plant that can thrive in disturbed soil—was present at 70% of the sites surveyed.
Timeline
1700s-1960s: Non-native ungulates were introduced to Hawaiʻi.
August 2023: Wildfires occurred on Maui.
September 2026: The study was published in Rangeland Ecology & Management.
The Tech Race
This study follows the precedent of the August 2023 Maui wildfires by quantifying how ecosystem disturbances like invasive grazing affect landscape resilience. Researchers are now attempting to map the specific correlation between ungulate density and post-fire invasive plant colonization.
Local ranchers may face increased operational costs as forage availability for livestock remains suppressed by the island's 47,000 axis deer. The presence of fireweed at 70% of sites also suggests potential risks for cattle health and land management practices.
The takeaway
The study confirms that invasive axis deer populations are significantly constraining the productivity of Hawaiʻi ranchlands. Stakeholders should monitor future reports from the University of Hawaiʻi at Mānoa for further data on the spread of fireweed in these grazing environments.
Further reading
For more on plant ecosystem dynamics in the islands, explore the latest research in Botany.
Source note: This article includes information reported by Maui Now | Hawaii News | Local Maui News and Information | Hawaii News.
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