The Battle to Slow Rapid ʻŌhiʻa Death in Hawaiʻi
Rapid ‘Ōhi‘a Death and healthy ‘ōhi‘a trees: Side by side, Rapid ‘Ōhi‘a Death has decimated ‘ōhi‘a forests across Hawai‘i Island since 2010. In 2020, this location along Stainback Highway in Hilo suffered over 75% mortality. Dead trees in foreground sit near healthy trees. The ROD resistance program is collecting cuttings from healthy trees like these to test and see if could be used to breed resistant stock for outplanting. (Photo courtesy of J. B. Friday)
Amy Androff, Pacific Southwest Research Station
Cheryl Laughlin, Pacific Southwest Regional Office
Note: With February as National Invasive Species Month in Hawaiʻi, the Forest Service explores the partnership with native Hawaiians to curb one of the deadliest tree fungi on the island.
The names of many plant pathogens appear almost manageable at first glance — like white pine blister rust or brown spot needle blight. They take their time in taking over a tree, giving us more time to fight back. But in 2015, when Rapid ʻŌhiʻa Death was first formally reported on the island of Hawaiʻi, scientists didn’t mince words in the naming.
From the outset, landowners were noticing their trees rapidly declining. “People were telling us the tree went from healthy to yellow to brown in two weeks, and two weeks later, it’s losing its leaves,” shared J. B. Friday, Extension Forester at the University of Hawaiʻi, in the documentary Saving ʻŌhiʻa.
Scientists found two different fungi causing Rapid ʻŌhiʻa Death, and Hawaiian cultural practitioners helped name them — Ceratocystis lukuohia and Ceratocystis huliohia. By the time brown leaves appear on the tree, it’s already too late. The Ceratocystis has worked its way into the core of the tree to start replicating and blocking the tree’s ability to take up water.
It takes multiple infections of C. huliohia before the tree dies. With the other fungus, C. lukuohia, it’s only a short time before the tree succumbs to the damage. So far, this more destructive fungus has been found on two of Hawaiʻi’s islands.
Currently, the best theory on how the fungi spread from tree to tree has been linked to boring beetles. As a beetle chomps into a tree infected with Rapid ʻŌhiʻa Death, it pushes out frass — or the sawdust and woody droppings produced from colonizing a tree. Mixed in that frass are Rapid ʻŌhiʻa Death spores. And there they wait for the wind, animals, humans or water to carry them to the next tree. When the fungus lands on a tree wound, it restarts its deadly journey into another tree’s core.
How young ‘ōhi‘a trees should look — a healthy flush of bright new leaves that regenerated after Rapid ‘Ōhi‘a Death (ROD) killed the entire stand of overstory about 10 years prior. ROD does not seem to be affecting young seedlings here in Pahoa, Hawaiʻi, 2021. (Photo courtesy of J. B. Friday)
“Playing out an average mortality rate of 10% per year, you’re going to see 100% mortality in a given ʻŌhiʻa stand in less than 20 years,” Flint Hughes, Research Ecologist with the Pacific Southwest Research Station in Hilo, Hawaiʻi.
To better understand why losing the ʻōhiʻa forests would be so devastating, it’s important to know the ʻōhiʻa tree is a keystone species on the Hawaiian Islands. A keystone species is a plant, animal, or microorganism a whole ecosystem depends on. The loss of a such an important species would rapidly and fundamentally change the overall structure of an ecosystem. In a short period of time, this environment would unravel and become unrecognizable as the beloved destination it is today.
The importance of saving the ʻōhiʻa tree is apparent by looking out on any of the islands’ landscapes. It grows in dry areas, as one of the first plants to sprout on bare lava rock, and as the largest trees in the mossy rain forest. The tree makes up 80% of native forests and plays a major role in the local culture and economy.
From the outset, the people of Hawaiʻi quickly mobilized to prevent the spread of the fungi to protect the forest, from passing laws to shifting Hawaiian cultural gathering practices. Many even forego gathering cuttings and collecting the bright flowers for celebrations, for fear of spreading the disease.
Lessons Learned for All Tree Diseases
Because of Rapid ʻŌhiʻa Death’s devastating swiftness and the ecological and cultural vitality of the islands at risk, there was no time to lose. Just months after ROD’s discovery, researchers and locals mobilized to prioritize, diagnose, and mitigate the effects of this invasive disease. Extension and outreach teams held hundreds of community meetings and developed a website with information and educational materials.
A quarantine was put into action. Infected materials were prevented from being transported between the islands. Land managers, USDA Forest Service Institute of Pacific Islands Forestry researchers, USDA Agricultural Research Service (USDA ARS), and scientists from University of Hawaiʻi Cooperative Extension Service messaged the public to contain the disease.
Frass, or the sawdust produced by ambrosia beetles, after they bore into the wood of dead trees. This ‘ōhi‘a tree in Kalopa State Park, Hawaiʻi, was killed by Ceratocystis lukuohia, a fungus causing the tree disease Rapid ‘Ōhi‘a Death. When the frass is blown by the wind, it can spread the disease. (Photo courtesy of J. B. Friday)
This united messaging was a crucial tool that allowed researchers and land managers to drop everything, to pivot and prioritize efforts to addressing the new pathogen. For example, Lisa Keith, USDA ARS Research Plant Pathologist, was able to track down the fungus and quickly develop tests to diagnose Rapid ʻŌhiʻa Death within a few months.
But it’s not just researchers and land managers doing all the heavy lifting. Community outreach was critical. Effective bridges were built with the Hawaiian community and with kumu hula (hula teachers), who shared messaging about how to adjust forest gathering practices to prevent spread of the disease.
Today, there is a sustained effort, connection and collaboration among many partners across Hawaiʻi. This network works to slow the damaging effects of Rapid ʻŌhiʻa Death through regular meetings. They share updates and new strategies around research, outreach and monitoring. Plus, a statewide working group meets with subgroups for science and outreach.
“Every group stepped up to address the threat,” shared Flint Hughes, Pacific Southwest Research Station ecologist.
Want to learn more about how Hawai’i is combatting this invasive species?
Check out some of these publications:
- High-resolution mapping of Hawaiian Metrosideros forest mortality using laser-guided imaging spectroscopy | US Forest Service Research and Development (usda.gov)
- Early detection of a tree pathogen using airborne remote sensing | US Forest Service Research and Development (usda.gov)
- Evolving threat of Rapid ‘Ōhi‘a Death (ROD) to Hawai‘i's native ecosystems and rare plant species
- Framework for establishing a Rapid ʻŌhiʻa Death resistance program
- Spatial patterns of ‘ōhi‘a mortality associated with Rapid ‘Ōhi‘a Death and ungulate presence
- Rapid ʻŌhiʻa Death Strategic Response Plan 2020-2024