rapid ohia death — Maui Invasive Species Committee (MISC)

Protecting ‘Ōhi‘a: Fencing for the Trees

Posted on July 27, 2023 by MISC

Ungulate rubbings or browsing on Haleakalā sandalwood tree are seen in Polipoli. — FOREST AND KIM STARR photo

“The fungus needs an entry point,” says Marc Hughes, a research plant pathologist with the U.S. Forest Service in Hilo. He’s talking about the disease that is decimating ‘ōhi‘a lehua in parts of Hawai‘i. An untreated scrape on a person’s skin can lead to a staph infection; a similar but more drastic result is true for ‘ōhi‘a. When some external force breaks through a tree’s bark, invading pathogens can gain access to exposed tissues, and damage or kill the tree.

Ceratocystis lukuohia and Ceratocystis huliohia are fungal pathogens that cause the disease called rapid ‘ōhi‘a death, or ROD, so named because the trees appear to die within days or weeks. Both pathogens will kill ‘ōhi‘a trees, but lukuohia is more aggressive. Once infected, the tree responds, trying to slow the disease.

“It’s like a speed race,” explains Hughes, “but the fungus is faster.”

The crowns turn yellowish, then brown. The tree looks frozen, dead leaves still attached. By the time an ‘ōhi‘a tree shows symptoms, its days are numbered. Since it was first identified in 2014, rapid ‘ōhi‘a death has killed over a million trees, mostly on Hawai‘i Island, but trees on O‘ahu and Kaua‘i have also succumbed. A single infected tree was discovered and removed in East Maui in 2019 and, to date, is the only known occurrence in Maui Nui.

Wounding is a prerequisite. Plants with intact bark don’t become infected, even when directly exposed to the fungi. How does wounding happen? Wind is one way, says Hughes, who describes Tropical Storm Iselle as a “mass wounding event.” The 2014 storm battered portions of Hawai‘i island, breaking ‘ōhi‘a branches and toppling trees. Researchers observed a spike in ‘ōhi‘a mortality after the storm and linked the spread to increased windborne spores and tree damage. Ambrosia beetles, which may burrow into trees killed by rapid ‘ōhi‘a death, also play a role. Fungus-contaminated frass — the sawdust produced when beetles bore into wood — gets picked up by wind, animals and hikers’ boots, or falls into the soil. Studies indicate a strong tie between the presence of ungulates, such as pigs, cattle and goats, and rapid ‘ōhi‘a death. The large numbers of axis deer on Maui, Molokai and Lāna‘i likely mean ‘ōhi‘a trees in Maui Nui could be especially vulnerable if rapid ‘ōhi‘a death were to become established here.

The study on Hawai‘i island found that unfenced areas, where ungulates were present, had two to 69 times more evidence of rapid ‘ōhi‘a death-impacted ‘ōhi‘a than neighboring, fenced areas that were ungulate-free. Researchers are also looking into the relationship between ungulates and the presence of the fungi in soil samples. Initial results indicate a similar link: the presence of ungulates means a higher likelihood the destructive fungus will be detected. Flint Hughes, a research ecologist also with the U.S. Forest Service (and unrelated to Marc), thinks pigs may spread the fungus through ‘ōhi‘a roots when they dig up the ground searching for food.

While the potential scale of impacts to ‘ōhi‘a might seem overwhelming, there is hope. In 2022, students on Oahu helped convinced the Legislature to designate ‘ōhi‘a lehua as the Hawai‘i State Endemic Tree, honoring its importance to the ‘āina and Hawaiian culture. Protecting forests through fencing, ungulate removal and ongoing maintenance, is a straightforward strategy, and one that watershed partnerships across the state are already working to implement.

This strategy has public support. A recent survey conducted for the Coordinating Group on Alien Pest Species found that 89 percent of respondents know about ‘ōhi‘a and 80 percent had heard of rapid ‘ōhi‘a death. An impressive 93 percent supported fencing of high-value forests and removing ungulates to protect ‘ōhi‘a from rapid ‘ōhi‘a death. Support may also be coming from federal coffers. This March, the Hawai‘i congressional delegation announced efforts to secure $55 million over a 10-year period for rapid ‘ōhi‘a death-related research and management.

In closing comments during a 2022 presentation, Flint Hughes offered a reminder: “We tend to think of ‘ōhi‘a as forests. Every ‘ōhi‘a tree is an important individual. Some of these trees are 300 or 400 years old. We should respect that and them, and do what we can to protect them.”

To learn more about how to support efforts to protect ‘ōhi‘a, visit www.rapidohia death.org.

* Teya Penniman is the interim manager with the Maui Invasive Species Committee. She has 30 years’ experience in natural resource management and advanced degrees in law and management. “Kia’i Moku, Guarding the Island” is written by the Maui Invasive Species Committee to provide information on protecting the island from invasive plants and animals that threaten our islands’ environment, economy and quality of life.

UPDATE November 2023: Learn more about the correlation between tree damage and Rapid Ohia Death in the interactive storymap from the ROD Working Group

This article was originally published in the Maui News on April 8, 2023 as part of the Kia‘i Moku Column from the Maui Invasive Species Committee.

ʻŌhiʻa’s genetic diversity may contribute to disease resistance

Posted on November 23, 2020 by Lissa Strohecker

The natural genetic variation in ʻōhiʻa may translate to some resistance to Rapid ʻŌhiʻa Death. To both preserve the genetic diversity present in ʻōhiʻa and test for disease resistance, there are seed banks established throughout Hawaiʻi. — Masako Cordray photo

ʻŌhiʻa is both a pioneer – the first to grow on new lava– and a protector—hosting and sustaining birds, insects, and plants throughout Hawaiʻi. ʻŌhiʻa is at home in nearly every terrestrial ecosystem in the islands, from the wettest rainforests to the leeward slopes of dryland forests. Its flowers range from cool yellow to fiery red. Leaves can be small, curled and fuzzy, and snuggled together along the stem, or stretched, shiny and drooping. The tree may crawl, bonsai-like on mountain tops, or assume a stately, spreading pose above the rainforest. The plant’s scientific name, Metrosideros polymorpha, only begins to reflect the “many morphs” of ʻōhiʻa. ʻŌhiʻa exhibits so much variation that taxonomists have classified the tree into different species and varieties, seven of which occur on Maui.

While ʻōhiʻa is amazingly adaptable, the reliance of so much native biota on its existence exposes a vulnerability. Without ʻōhiʻa, our forests – dryland to mesic to the rainforest – and the species within them are in peril. Rapid ʻŌhiʻa Death, the fungal disease that has killed ʻōhiʻa across 135,000 acres of Hawaiʻi Island, and counting, makes this abundantly clear. The discovery of this pathogen on Kauaʻi in 2018 further underscores the risk, even though it is not yet known from the other islands.

“The goal is to preserve the genetic diversity of ʻōhiʻa naturally present in the landscape,” says Dr. Marian Chau.

Ripe ʻōhiʻa seeds being grown on the Hawaiian Islands for the preservation of the native species. —

One source of hope is that ʻōhiʻa’s high degree of genetic diversity could contain the key to disease resistance. Across the state, foresters and conservation groups are partnering on a project to collect and store seeds in ʻōhiʻa seed banks. “The goal is to preserve the genetic diversity of ʻōhiʻa naturally present in the landscape,” says Dr. Marian Chau, seed lab manager at Lyon Arboretum on Oʻahu. “The seeds can be used for current research on potential genetic resistance to Rapid ʻŌhiʻa Death, and for future restoration.” ʻŌhiʻa produces plentiful seed that can be stored for up to 18 years. To preserve and represent this variation, the seed collection campaign has a lofty goal of obtaining seeds from 10,000 different trees of fourteen different species.

Each island is divided into seed zones and collectors record the zone where they harvest seeds. If there is no representation from a particular zone, Chau and her colleagues reach out to those working in the area. The Laukahi Hawaiʻi Plant Conservation Network, a voluntary alliance focused on protecting Hawaiʻi’s rare plant species, created the seed zones and manages the data.

Throughout Hawaiʻi, partnerships have been made to collect wild-grown ohia seeds. There are currently more than four million seeds in the collection — Laukahi Network photo

With support from the Hawaiʻi Tourism Authority, Chau has traveled across the state offering free training on how to properly collect ʻōhiʻa seeds. Her workshops cover identifying the variety; determining if seeds are ripe; cleaning and packaging ʻōhiʻa for storage; and recording and submitting collection data. The trainings are empowering community participants to help stop the devastation of Rapid ʻŌhiʻa Death. The workshops are open to the public, but only naturally-occurring ʻōhiʻa are candidates for seed banking, not landscape-planted trees. To collect seeds from ʻōhiʻa in the wild, landowner permission and necessary permits for state or federal land are required.

To guard against inadvertent destruction (e.g., from a tropical storm), the seedbanks are scattered throughout the state, with redundant banks in different locations. Hawaiʻi Island seeds are stored on that island due to concerns about the accidental spread of the disease.

You can find more information about seed banking efforts online at http://laukahi.org/ohia/ including ʻōhiʻa identification information, seed collection guidelines, data collection, and needs. Learn more about Lyon Arboretum’s Seed Conservation Laboratory at manoa.hawaii.edu/lyon/research/hrpp/. Stay up to date on Rapid ʻŌhiʻa Death at rapdiohiadeath.org and through the Rapid ʻŌhiʻa Death Facebook Page.

Lissa Strohecker is the public relations and education specialist for the Maui Invasive Species Committee. She holds a biological sciences degree from Montana State University. Kia’i Moku, “Guarding the Island,” is prepared by the Maui Invasive Species Committee to provide information on protecting the island from invasive plants and animals that can threaten the island’s environment, economy, and quality of life.

This article was originally published in the Maui News on June 9th, 2019 as part of the Kia‘i Moku Column from the Maui Invasive Species Committee.

Drones help field crews find invasive species

Posted on November 22, 2017 by Lissa Strohecker

Would you rather walk across this lava field to look for invasive plants or search by air? Drones are increasing the efficiency of invasive species field crews on Hawaiʻi Island. Photo by T. Sullivan, BIISC.

Your mission: find a few invasive silk oak trees scattered across a 35,000-acre ancient cinder cone that resembles a bundt cake. Dead-ends and backtracking are the norm as you navigate up and down and across the slope, trying to locate and reach the trees.

Such is the task facing the crews of the Big Island Invasive Species Committee (BIISC) as they endeavor to control silk oak trees on the slopes of Puʻu Waʻawaʻa (literally translated to “many furrowed”) near Kona. They now have help from a set of eyes in the sky.

Using a drone, or unmanned aerial vehicle (UAV), the crews can find the best path across the landscape, saving time and allowing them to more efficiently do what they do best: get rid of invasive plants.

“It works best on a large landscape,” explains Timo Sullivan, BIISC’s early detection and remote sensing specialist. “You can trade 8 hours of hiking for 2 hours of controlling,” he says. Sullivan’s work with BIISC began a few years ago when they were exploring ways to identify invasive Australian tree ferns hidden within vast eucalyptus plantations. Today, the drone is almost a part of the field crew, scouting out the best route or even finding plants the crew is searching for.

Timo Sullivan uses drones to help the field crews from the Big Island Invasive Species Committee find invasive plants. Photo courtesy T. Sullivan, BIISC.

“It works best with species you can see above the canopy” he says. BIISC relies on UAVs to help survey for rapid ʻōhiʻa death, a fungal disease affecting ʻōhiʻa trees on Hawaiʻi Island. The main symptom: the leaves turn brown almost overnight, as though frozen in place. “It’s surprisingly hard to tell if a tree in the canopy is dead when you are on the ground,“ says Sullivan.

Typically, he arrives at a field site a few hours before the crew and spends an hour flying the drone, followed by an hour viewing the footage on the laptop. Then the crew can head straight to the plants on the ground. It’s possible for Sullivan to cover 40 acres in an hour. This is a big shift from the past efforts where crews spent all day hiking to find maybe 10 plants. “It’s been a huge morale booster,” he says. “Crews feel more successful when they can actually remove plants rather than search for them all day.”

The drone BIISC uses is nothing fancy, just a consumer model with a GoPro attached to record what’s seen. The footage can be reviewed on the spot or later. Instead of three sets of tired eyes scanning from a helicopter, the footage can be shared with many, including researchers looking at native plants or other aspects of the landscape. A manager can see what the crew faces, as well as document change over time.

The technology has limitations though: searching for plants under the canopy is still a task for ground crews, and the drone has to remain in the line of sight of the operator. Surveying in Kīpahulu valley while sitting miles away in Makwao is currently not possible.

Miconia (circled in red) has large leaves with a distinctive leaf pattern. Researchers at the University of Hawaiʻi are looking at ways to train computers to analyze drone footage to find miconia. Photo courtesy of T. Sullivan, BIISC.

Researchers are investigating ways to take drone usage to the next level. Roberto Rodriguez, a PhD student at the University of Hawaiʻi-Manoa is helping to determine the ideal speed at which to review footage. Heʻs researching computer programs that analyze the footage. “Miconia is a nice initial plant to work with,” he says. “The large leaf size and distinct vein pattern is something a computer could identify.” They researcher can then take what they learn and modify it for other species.

Ground crews can’t hang up their boots entirely. They can’t get ahead of an invasive species’ seeding cycle until they remove every young plant before it goes to seed—and small understory plants typically aren’t visible from the air. Drones are just another tool. There may come a day when crew each has its own drone, enabling workers to easily glance at a gulch or a steep, inaccessible cliff to make sure no invasive plants remain.

To learn more about research and drone usage for conservation in Hawaiʻi check out http://spatial.uhh.hawaii.edu/index.htm.

This article was originally published in the Maui News on April 9th, 2017 as part of the Kia‘i Moku Column from the Maui Invasive Species Committee.

Rapid ʻŌhiʻa Death – a new threat to our watersheds

Posted on May 19, 2015 by Lissa Strohecker

This ohia tree shows one of the characteristic symptoms of Rapid ʻŌhiʻa Death – the tree looks frozen or burnt, leaves still in place. Photo by J.B. Friday
This ʻōhiʻa tree shows one of the characteristic symptoms of Rapid Ohia Death – the tree looks frozen or burnt, leaves still in place. Photo by J.B. Friday

Five years ago, people living in the Puna district on Hawaiʻi Island started seeing native ʻōhiʻatrees in their yards dying. First, the leaves on a single limb or the whole tree would start to yellow and brown. Within days or weeks, the tree would be dead. “Trees look burnt or frozen,” explains Dr. Flint Hughes, a research ecologist with the USDA-Forest Service. He’s one of several scientists investigating the cause of Rapid ʻŌhiʻa Death, an apt description for a disease causing ʻōhiʻa to die so fast they don’t have time to drop their leaves.

Symptoms can appear in a single branch or the entire canopy of a tree. Pruning the affected brance will not save the tree since the Ceratocytis fungus is already established in throughout the tree. Photo by J. B. Friday

The disease spreads across landscapes nearly as fast. In 2012, it had killed ʻōhiʻa across about 1000 hectares (nearly 2500 acres). By last summer, it covered 6000 hectares. Healthy trees, young trees, old trees–it doesn’t matter—once symptoms appear, the tree will be dead within weeks.

A disease this virulent is potentially catastrophic for native species and watersheds. ʻōhiʻa are a keystone species for a Hawaiian rainforest. Like the uppermost stone in an arch, ʻōhiʻa is critical to the structure and function of the forest, both as refuge for native birds and other species, and as an effective way to transform what falls as rain into what comes out of the tap.

Last year, Hughes and his colleagues began to research what was happening. They knew it was a new phenomenon and not related to any previously known problems in ʻōhiʻa, such as ʻōhiʻa dieback or ʻōhiʻa rust. Within six months they had isolated the pathogen causing Rapid ʻŌhiʻa Death. The disease is caused by a fungus, Ceratocytis fimbriata. It gets into the sapwood of ʻōhiʻa, stopping the tree’s ability to transport water and sugars. “The fungus essentially strangles the tree,” says Hughes.

The ceratocytis fungus responsible for killing ohia accross 15,000 acres on Hawaii Island can be seen as a dark staining in the sapwood. Photo by J.B. Friday

Isolating the cause of Rapid ʻŌhiʻa Death, also called Ceratocytis wilt of ʻōhiʻa, is the first step. Ceratocytis has been present in Hawaiʻi for decades. In the Islands, it’s known only as a pathogen on sweet potato and taro, never before attacking ʻōhiʻa. In other parts of the world, Ceratocytis infects sycamore, eucalyptus, mango, coffee, cacao, citrus, poplar, fig, and rubber trees.

Researchers have yet to determine the origin of this recent outbreak—more than likely a new, more virulent strain of Ceratocytis was introduced but it is possible the existing strain jumped to ʻōhiʻa.

One of the researchers’ top priorities is determining how the disease is spreading. Other places

The Ceratocytis fungus spreads throughout the sapwood or vascular system of the ohia, eventually strangling the tree. The dark staining in this cross-section of an ohia is a symptom of infection by the Ceratocytis fungus. Photo by J.B. Friday

in the world, insects and contaminated equipment are vectors for spreading Ceratocytis, and that could be the case in Hawaiʻi. Until that’s determined, Hughes urges people not to move ʻōhiʻa—logs or seedlings. The fungus can survive in dead logs for a year or more. He suggests that it’s even possible that Ceratocytis spores may land on plants growing near ʻōhiʻa and movement of those plants may spread the disease

On Hawaiʻi Island some of the nicest stands of low-elevation ʻōhiʻa are gone, but researchers are not giving up. “One of the hopes is that we’ll see some genetic resistance in ʻōhiʻa, or there may be environmental constraints,” says Hughes. On Hawaiʻi Island, Ceratocytis has been found as high as about 1,400’ elevation in Mountain View, but that may reflect the relatively recent introduction rather than the full extent of its potential range.

Fungal spores of Ceratocytis on a dead log. The fungus can survive in dead logs for a year or more, and the disease can infect the plants for 2-3 months before symptoms appear. Help stop the spread by not moving ohia-logs or seedlings. Photo by J.B.Friday

They do know that the fungus can be present for months before any symptoms appear. During pathogenicity testing, ʻōhiʻa trees showed symptoms two or three months after inoculation. Pruning a symptomatic branch will not necessarily protect the tree as the fungus may have already spread throughout the tree and possibly to nearby trees.

Researchers have much to learn about Ceratocytis wilt on ʻōhiʻa. For now, they encourage people to clean boots and equipment after working on infested trees and caution against interisland movement of ʻōhiʻa logs and seedlings. Rapid ʻŌhiʻa Death is only known to occur on Hawaiʻi Island. If you are on Maui or elsewhere in the Islands and see symptoms: leaves quickly turning yellow or brown, dead trees looking burnt or frozen with leaves still in place, or tell-tale brown streaking on the dead wood, contact Hughes by phone, 808-854-2617, or e-mail fhughes@fs.fed.us Learn more online at http://www2.ctahr.hawaii.edu/forestry/disease/ohia_wilt.html

Originally published in the Maui News, May 10th, 2015 as part of the Kia‘i Moku Column from the Maui Invasive Species Committee.

Protecting ‘Ōhi‘a: Fencing for the Trees

ʻŌhiʻa’s genetic diversity may contribute to disease resistance

Drones help field crews find invasive species

Rapid ʻŌhiʻa Death – a new threat to our watersheds

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