Disease could kill most of the ‘ohi‘a forests on Hawaii’s Big Island within 20 years

Ten years ago, a mysterious new disease was found sweeping through Hawaii’s native ‘ohi‘a forests, killing off the foundation of the islands’ ecology and one of the state’s most culturally important trees.

Now, researchers are in a race against time. They say most of the vast ‘ohi‘a forests on Hawaii island will be gone in the next 20 years if what’s come to be known as Rapid ‘Ohi‘a Death — ROD — isn’t stopped.

That has teams of scientists gunning to better understand how the fungal disease works to help state and federal land managers better protect the vulnerable forests.

Recently, some promising developments have occurred. They include a novel beetle repellent to keep away the tiny bugs that help infect the ‘ohi‘a trees with the virus and a $1 million grant to study whether the chemistry makes some trees more resistant than others.

Ultimately, saving the ‘ohi‘a, a plant unique to Hawaii on which thousands of other plant and animal species depend to survive, will require more money.

In January, a multi-agency working group is set to release its latest five-year plan to fight the disease. State land officials say carrying the plan out could require as much as $8 million per year — about double the amount called for in earlier plans.

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The previous Rapid ʻOhiʻa Death Strategic Response Plan, covering 2020 to 2024, called for just over $4 million per year. The researchers and managers behind that plan included only the highest priority items, but Rob Hauff, a state protection forester with the Department of Land and Natural Resources, said actual allocations fell short by up to $1 million.

He said he hopes the state and federal leaders will fully fund the next five-year plan, adding that “it’s easy for things like this to fall off the radar.”

Climate change, meanwhile, is hastening the ‘ohi‘a die-off.

Warming conditions lead fast-growing invasive plants and weeds such as ginger and strawberry guava to choke out young ʻohiʻa trees and other native plant species on the forest floor, researchers say.

Extended drought linked to climate change further stresses the o‘hi‘a trees, and more frequent storms leave them with broken branches with exposed bark. Those factors make them more vulnerable to the disease, according to Sarah Knox, a project coordinator with the nonprofit Akaka Foundation for Tropical Forests.

“Everyone feels a pretty big sense of urgency to work on this from as many angles as we can,” Knox said. “Every approach possible is being explored.”

The Backbone Of The Forest

The ʻohiʻa is what researchers call a “keystone” tree for Hawaii, supporting scores of native plants, insects, birds and the overall ecology.

The trees are strong and durable, with papery bark and trunks that twist as they grow. Their coin-shaped leaves can be either fuzzy or smooth, and their lehua blossoms come in a variety of colors, although they’re mostly red.

When the trees fall, Knox said they spend about twice as much useful time on the ground as logs, helping to nurse along new trees and plants, as when they stood upright.

On the Big Island, they’re everywhere, growing on dry lava flows and in wet, boggy areas. Their forest canopies capture the island’s fresh water supply by catching the cloud mist as it drifts by. Their shade keeps that moisture from evaporating back into the sky. The forest ground cover can slow the water’s flow and prevent flooding.

The tree also plays an integral role in traditional Hawaiian cosmology and belief, according to Lilikala Kameʻeleihiwa, a senior professor at the University of Hawaii’s Hawai‘inuiakea School of Hawaiian Knowledge.

It’s closely linked to Pele, the Hawaiian goddess of fire and volcanoes and Ku, the Hawaiian god of primal energy and war. Hula dancers would often collect its flowers and leaves to craft lei and make offerings to Laka, the Hawaiian goddess of hula.

Hawaiians also used ‘ohi‘a wood to create the carvings that adorned their stone temples, Kame‘eleihiwa said. Those carvings made the temples a sacred place for the akua, or divine elements, to inhabit.

Halau, or Hawaiian hula groups, still gather those flowers and leaves, although researchers now advise those groups not to take them to neighboring islands to avoid spreading the disease.

ROD, caused by a fungus called ceratocystis, has been found in some forest pockets of Kauai, Oahu and Maui but has yet to explode across those islands as it has on the Big Island.

In the past decade, the disease has killed between 1 and 2 million trees in Hawaii, according to Flint Hughes, a Hilo-based research ecologist with the U.S. Forest Service.

Overall, Hawaii has some 300 million ʻohiʻa remaining, but Hughes and others said ROD disproportionately affects the limited pool of 17 million large, more mature trees that predominantly make up the forests. Hughes said the infected forest plots that are being watched tend to lose about 10% of their trees per year.

“That’s why it’s so dire,” he said.

There’s some disagreement among the Hawaiian halau and broader community over what collection practices remain acceptable given the threat, and wildlife officials are trying to draft clearer guidelines, according Kylle Roy, a forest entomologist with the U.S. Fish and Wildlife Service.

Roy and other researchers have recently been studying precisely how the disease spreads at higher forest elevations. “People want to blame one thing for spreading ROD, but different things can happen at different places,” she said.

Roy has been developing a wax-like repellent that, when applied to an ʻohiʻa tree’s trunk, could trick the ambrosia beetles into staying away. It would release pheromones that make the beetles think the tree is already dead, she said, and not worth boring into.

Trying to stop Rapid ʻOhiʻa Death is personal to Roy as a Native Hawaiian.

“It’s so clear on the Big Island how important it is. It is the native forest and everything depends on it,” she said. “I decided, once I was really in it, that I’m dedicating my life to saving ‘ohi‘a.”

Roy’s repellent would need state approval, which it could gain later this year for widespread use under what’s called a Special Local Need registration, according to Greg Takeshima, the state Department of Agriculture’s Acting Plant Industry Administrator.

If the state approves it, the repellent could be applied in the ‘ohi‘a forests even as it awaits final approval from the Environmental Protection Agency, Takeshima added. If the EPA raises any concerns then crews would have to stop until those issues are resolved.

Trekking Through The Forest Floor

During a recent field survey of ʻohiʻa trees in Hawaii Volcanoes National Park, the difference between healthy forest areas and those afflicted by disease and rampant pig activity was stark.

“If you look up, you can see the sky,” Roy said, pointing up at dead canopy branches whose leaves previously helped block some of the light streaming through. Few of the native hapu‘u ferns that grow on the ʻohiʻa trees or the matte uluhe ferns that form much of the forest ground remained. Without underbrush, it was easy to walk through the area.

However, in a nearby healthy section protected by fencing, thick fern covering made it difficult to move through the area.

Many of the damaged and dying ʻohiʻa areas in the national park are overrun with invasive plants. Stacey Torigoe, a National Park Service ecologist, works to slow the influx of those and other weeds using what are known as “bio-control” measures.

They include introducing special insects that feed solely on the strawberry guava, causing those plants to produce galls, or abnormal growths on their surface. The galls then slow the spread of the strawberry guava across the forest floor.

Keeping that understory as clear of invasive plants as possible is just as key to the effort as curbing the disease so that new trees and native species can flourish there.

Search For The Strongest Trees

Other researchers are trying to figure out what makes some trees more resilient than others — and to find those answers fast.

Tree scientists at Purdue University and the University of Wisconsin recently got a $1.1 million grant from the National Science Foundation and the U.S. Department of Agriculture to study ‘ohi‘a trees’ chemical defenses and what makes some more susceptible.

The research project focuses on carbohydrates as the building blocks of those chemical defenses, said said Morgan Furze, an assistant professor at Purdue’s tropical hardwood tree improvement and regeneration center.

She and others will examine whether trees genetically capable of storing more carbohydrates can better fend off the disease when it strikes.

Often in the past decade, aerial footage taken of infected forest patches has shown a few live trees in a sea of dead ones claimed by the disease.

“Perhaps if the tree stores more carb reserves, it’s better able to defend itself against the pathogens,” Furze said.

The findings could help forest managers pinpoint when the trees are at their most vulnerable to the disease and when it makes the most sense for crews to spray them with fungicide.

The three-year project complements a separate effort to collect ʻohi‘a cuttings and seeds from the forest, then use them to grow new trees in a nursery to determine which are genetically the most resistant to the fungus.

That effort by the Rapid ʻOhiʻa Death Resistance Program is a decades-long project because it requires growing trees big enough to seed, according to J.B. Friday, an extension forester for the University of Hawaii.

“Morgan’s research would be a big shortcut to that process of testing everything,” Friday said. “If you could go in the field and take some sort of measurement to know what’s resistant, that would really speed things up.”

With the disease threatening to annihilate Hawaii’s ʻohiʻa forests in the next two decades, he said, that shortcut could be critical.

Still, he added, the best option is to protect all the ʻohiʻa trees, regardless of their resiliency, to the extent that’s possible.

“It’s much more important to protect our forests than to replant them when they’re dead,” Friday said. “Having resistant ‘ohi‘a, it’s an important tool. But we should also be trying to protect our healthy forest.”

Protecting Fenceless Forests

One thing abundantly clear to Knox and other forest managers is that installing fences across the Big Island’s ‘ohi‘a forests would almost entirely stamp out Rapid ʻOhi‘a Death. The barriers keep out the pigs, goats and other invasive hoofed animals that can spread the fungus spores from tree to tree.

But installing fences across all 800,000 or so acres of forests — then maintaining them in that rugged terrain — simply isn’t feasible.

“Fences are wonderful; they’re also expensive,” Torigoe said.

The park service has about 170 miles of fencing across the Big Island’s Volcanoes National Park to keep out those hoofed animals, according to NPS spokesperson Jessica Ferracane. Maintaining and inspecting the fences is a huge job.

Since much of the national park’s nearly 72,000 acres of ʻohi‘a forest remain exposed to the pigs, researchers must continue to study the complex ways the disease spreads.

They know that pigs contribute to the spread by rubbing against the trees and wounding them, plus they further spread the disease when they dig and kick up dirt near infected trees that’s can be filled with the deadly fungal spores.

How the beetles, the pigs, the warming climate and the trees themselves all work together to spread ROD in different forest climates remains somewhat of a mystery, one the scientists are working to solve.

“We have kind of a good understanding of the important framework. Now we’re working out, where do factors differ across landscapes that affect tree mortality?” Hughes said. “And nailing those things down is very important for managers.”

Knox, for example, is trying to better understand what prompts the wild pigs to choose one tree to repeatedly rub against versus another. What attracts that pig to that tree?

Her team uses cameras installed in the forest to spy on the animals. They are investigating whether it would make sense to develop what she called “rub hubs” for the pigs — artificial posts that mimic the trunks.

Knox is also looking at which tree wounds are most effective at spreading the disease: those on the trunks or those on the wooden roots just under the ground. She said those findings could help crews more efficiently protect the forest.

“We’re adding to our tools as quickly as we can get them,” Knox said. “Managers only have so much manpower, time. You don’t want to send them down the wrong path.”

Some field surveys this summer suggested the trees’ fine roots even deeper in the ground may be vulnerable to infection. Researchers stress that’s far from conclusive but a major concern because of the hoofed animals, also known as ungulates.

If that’s the case, “boy, ungulates can quickly do a number on a forest because they’re wounding fine roots all the time,” Hughes said.

In Hawaiian tradition, Pele takes the ʻohiʻa trees on as her physical form, and all Hawaiian ancestry lives on in them, according to Kame’eleihiwa.

“Every time a tree dies it’s like one of our family dies, it’s really heartbreaking to us,” she said.

“It is a special, sacred tree. There’s a spirit of Ku — the spirit of energy that comes from the earth to the sky,” she added. The trees, she said, “become a sacred house for those elements to live in.”

“It would be wonderful if the scientists could learn how to stop the disease,” Kame‘eleihiwa said.

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This story was originally published by Honolulu Civil Beat and distributed through a partnership with The Associated Press.