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Researchers are closer to understanding a fungus that has infected 50,000 acres of Big Island ohia forest in little more than a handful of years.
But Rapid Ohia Death is still spreading, a real solution remains elusive, and even as communities rally to do their part, they are discovering they face two enemies instead of one.
“There are two species of fungus; both are new, both have never been described before,” said James Friday, a University of Hawaii College of Tropical Agriculture and Human Resources extension forester who is at the forefront of the battle against ROD, first discovered in the Puna District in 2010.
“It’s become more complicated than we thought,” Friday told Civil Beat.
A wholesale loss of ohia forests could crash fragile island ecosystems, put watersheds at risk and deprive endangered birds of food and habitat, among other grim outcomes.
Genetic finger-printing reveals that one strain of the fungus, Ceratocystis fimbriata, originated in Latin America, the other in Asia. Too new to have names, the strains have been dubbed A and B, respectively. The first is more virulent than the latter, but both kill ohia in a matter of weeks by colonizing and clogging the tree’s vascular system.
How the two strains came together from divergent points on the globe to be part of the same outbreak is a mystery that researchers have only begun to tackle.
The fungus known as Rapid Ohia Death has been spreading for years on the Big Island, killing the iconic trees as it goes.
Scientists are also trying to figure out how the disease moves through the forest. They have found the pathogen spreads a bit like a forest fire, flashing through an area, then smoldering along and sparing neighboring trees.
Then — like a spot fire out ahead of the main blaze — it flares up somewhere else.
“It’s not an inexorable spread. It moves like an outbreak,” Friday said.
All evidence points to wounded trees being the most vulnerable to infection, with wind-damaged branches and scarred trunks creating opening where the fungus can get itself established deep within the tree.
“It’s something we’re emphasizing more because we’ve seen a bunch of cases where wounded trees are infected and the rest of the trees are not,” Friday said.
Probably spread by a combination of human activity and airborne sawdust from wood-burrowing ambrosia beetles, the fungus crept into South Kona forests a couple of years ago. Those outbreaks have since mushroomed. The disease has also hopped north through the forests above Hilo and finally into Hamakua.
Can It Be Stopped?
In this latest spot, there are signs of hope for stopping the fungus in its tracks.
Foresters are going on the offensive, cutting down stricken trees and burying them while the infected area is still small. This attempt at containment — along with guidelines that urge the public to clean vehicles, tools, machinery and boots they have used in the woods — is the best game in town at the moment.
The disease isn’t shy in announcing itself, with signature fast-moving yellowing and then browning of the entire canopy of a tree or group of trees. The key is early detection.
As the public gets a better grasp on what the disease looks like and the threat it poses, landowners, farmers, residents, hula practitioners and others have joined in the fight. Realizing what’s at stake if the fungus goes island-hopping, a network of watershed partnerships and invasive species committees has formed across the state.
Friday communicates weekly with the groups. “They’re our eyes on ground in the remote ohia forests,” he said.
“It’s not an inexorable spread. It moves like an outbreak.” — UH forester James Friday
Scientists have tested dozens of samples sent in by concerned folks from various islands, but so far tests have all come back clean. An emergency measure in 2015 by the state Department of Agriculture halted the shipment of ohia products off island. The ban, made permanent last October, seems to be working, Friday said.
The state Division of Forestry and Wildlife and the Big Island Invasive Species Committee are spearheading ongoing mapping of infected areas based on helicopter overflights.
Lisa Keith, a researcher with the U.S. Department of Agriculture, is in the midst of screening four varieties of ohia, looking for resistance to ROD. It’s too early to tell yet which trees may stand up to the fungus, she said. Banking the seeds of fungus-resistant ohia could help ensure the future of the forest, which comprises around 50 percent of the state’s watersheds.
Researchers are also experimenting with fungicidal spray.
“Certain fungicides can kill the pathogen in the lab but results have been harder to interpret for potted seedlings,” Keith said.
The Importance Of Ohia
Ohia is a keystone species. By far the single biggest player in the forest, it’s the first tree to colonize bare lava, breaking basalt down into soil and providing the shade that allows other species to grab hold. It supports fragile native bird populations and countless other denizens.
A Ohia Lehua blossoms on the Big Island. The flowers would normally be used by halau in the upcoming Merrie Monarch Fesitival but performers are taking precautions.
Cory Lum/Civil Beat
In a culture where dieties are inextricably tied to nature, celebration of the tree is foundational to some hula practices.
Last year, many of the competing halau in Hilo’s Merrie Monarch Festival observed a voluntary kapu on using ohia in their costumes. Judges allowed the performers to substitute other plant material for the signature ohia sprigs. The measure was designed to prevent performers from transporting the disease off island when they went back home.
“They improvised with whatever they could get their hands on that was still a significant part of their dance,” said Luana Kawelu, president of Merrie Monarch.
For the 2017 competition, a team of ROD experts met with halau and judges to offer the latest information and field questions. Arrangements have been made so that any halau which do decide to harvest the ohia will have a way to dispose of the greenery in an area already infected with ROD.
“The ohia is such a precious part of hula,” Kawelu said. “We know the halau will take care of the trees.”
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