Environmental scientists publish online maps showing cattle, pigs spread Rapid ʻŌhiʻa Death

The maps stem from research first released in 2021 led by UH Hilo environmental scientist Ryan Perroy, director of the Spatial Data Analysis and Visualization research laboratory based at the university.


By Susan Enright.

A team of researchers from the University of Hawai‘i at Hilo and UH Mānoa are leading the charge on a statewide collaborative project to explore the relationship between hooved animals and the spread of Rapid ‘Ōhi‘a Death (ROD).

Map shows far greater ROD damage outside fenced areas.
Newly published online maps show a greater spread of ‘ōhi‘a die off in unfenced areas hooved animals can access.

From data produced during a collaborative study involving university, community, county, state and federal experts, maps of hard hit districts on Hawai‘i Island were recently released online that show the destructive role animals such as cattle and pigs can play in infecting ‘ōhi‘a trees with the fatal fungus, Ceratocystis lukuohia, that causes ROD.

Experts say ‘ōhi‘a make up 80 percent of Hawai‘i’s remaining native forests. Preventing or reducing damage from ROD and hooved animals is critical for protecting watersheds and only source of fresh water in Hawai‘i.

According to UH researchers, the animals damage healthy trees by digging up roots and stripping off bark. The damage makes the tree more susceptible to infection by the fungal spores carried in soil or the wind.

The researchers say fencing can help prevent the spread of the disease.

Ryan Perroy pictured
Ryan Perroy

The newly published maps stem from research first released in 2021 led by UH Hilo geographer Ryan Perroy, a professor of geography and environmental science and director of the Spatial Data Analysis and Visualization research laboratory, which is based at the university and plays a large part in the studies.

Perroy’s team revealed significant differences in areas on Hawai‘i Island with and without ungulates (hooved animals), suggesting that ungulate exclusion is an effective management tool to lessen the impacts of ROD in forested areas in Hawai‘i.

About the just-released online maps, Perroy says, “ROD continues to kill trees and negatively impact our native forests, and it’s important to make sure the public is aware of this ongoing issue. Publicly-accessible maps, like the ones produced as a result of this collaboration, are valuable for getting that message out and visualizing the differences measures like fencing and ungulate removal can have on forest health.”

Feral pig stands against a fence line.
Hooved animals rub against or strip bark wounding the tree allowing deadly fungus to infect ‘ōhi‘a.

Perroy credits Brian Tucker, a ROD data specialist at UH Mānoa Pacific Cooperative Studies Unit through the university’s Research Corporation, with pushing the story map project forward to online publication. Story mapping is a technique that can help the public visualize and understand complex scientific data.

Tucker says the surveying and monitoring of ʻōhiʻa forests remains one of his agency’s top priorities.

“These observations help guide our research projects, forest management practices and public outreach,” says Tucker. “We noticed a trend where the forests have less mortality due to ROD when protected from feral animals, especially cattle and pigs. We love our forests and it gives us hope because there are tools available for meaningful action to minimize the most devastating effects of ROD.”

The data

Spatial data was collected using remote-sensing technology, high-resolution satellite, and helicopter imagery obtained from January 2019 through January 2023. In 2022, a new aerial device designed by Perroy’s research team was used to collect larger ‘ōhi‘a branches to test for Rapid ‘Ōhi‘a Death in Hawai‘i’s forests and led to a higher rate of successful diagnostic testing.

The data from the four-year study shows a greater spread of ‘ōhi‘a die off in unfenced areas that hooved animals can access and significantly lower ‘ōhi‘a mortality in forest areas where hooved animals are blocked out by fencing.

Naiʻa Odachi pictured
Nai‘a Odachi

Analysis of the remote-sensing and high-resolution satellite imagery occurred collaboratively with researchers at the UH Hilo Spatial Data Analysis and Visualization laboratory, with UH Hilo student geospatial analyst Nai‘a Odachi performing much of the work. The lab specializes in geospatial technology, which is integral in obtaining aerial imagery to detect ‘ōhi‘a mortality at an individual tree level.

“Remote sensing using aerial and high-resolution satellite imagery has allowed researchers to expand monitoring capabilities on Hawai‘i Island,” says Odachi, who is pursuing a master of arts in tropical conservation biology and environmental science at UH Hilo. “This imagery is used to identify individual dying ‘ōhi‘a trees and can be used to direct field crews for sampling and ultimately lab analysis to confirm ROD infection.”

At the 2023 Hawai‘i Conservation Conference held in June, Odachi presented ROD investigations she conducted at UH Hilo’s Spatial Data Analysis and Visualization laboratory and won the Outstanding Graduate Student Oral Presentation Award.

Statewide problem, statewide collaboration on the research

‘Ōhi‘a mortality has been observed in every district on Hawai‘i Island, with some areas showing very high rates of mortality. In October 2022, high-resolution satellite imagery analysis of two equally sized areas across the fenced boundary of Hawai‘i Volcanoes National Park showed 99 percent of the 3,398 suspected trees impacted by ROD were in the unfenced area.

Map shows far greater ROD damage outside fenced areas.
Newly published online maps show a greater spread of ‘ōhi‘a die off in unfenced areas that hooved animals can access.

Outbreaks with significant ROD mortality were also reported on Kaua‘i.

This study is a statewide collaborative project. The UH researchers teamed with the Department of Land and Natural Resources (DLNR), Department of Hawaiian Homelands, The Nature Conservancy, National Park Service, and U.S. Fish and Wildlife Service to assess data from forested areas within Hāmākua to Ka‘ū on Hawai‘i Island. The project is funded by the DLNR and the U.S. Department of Agriculture Forest Service.

This collaborative research is geared toward building upon effective management strategies already in place to help protect Hawai‘i’s remaining ‘ōhi‘a, and increase native forest regeneration and restoration.

Read more at UH System News.

Related stories

Environmental scientists show link between rapid ‘ōhi‘a death mortality levels and hoofed mammals

UH Hilo’s Nai‘a Odachi wins Outstanding Graduate Student Oral Presentation at Hawai‘i Conservation Conference

Researchers design more effective aerial device to collect Rapid ‘Ōhi‘a Death samples


Susan Enright is a public information specialist for the Office of the Chancellor and editor of UH Hilo Stories. She received her bachelor of arts in English and certificate in women’s studies from UH Hilo.