Rapid 'Ōhi'a Death: The Disease That's Killing Native Hawaiian Trees
Deep in the forests of Hawaii, a native tree called 'ōhi'a reigns king. The tall canopy tree dominates the island's forests, especially on the Big Island. 'Ōhi'a makes up approximately 80 percent of Hawaii's native forests and more than half of 'ōhi'a grows on Hawaii Island.Often the first plant to grow from a fresh lava flow, 'Ōhi'a is known for its resilience. That's what makes a recent discovery all the more tragic: 'ōhi'a is dying.
"This is our everything tree. It's the most wide spread, it's the foundational species for our forests. If we lose 'ōhi'a, it will transform our forests."
The disease, called Rapid 'Ōhi'a Death, was first spotted on the eastern side of the Big Island. In an area called "Ground Zero," scientists observe land that was once lush, green rain forest. It's now barren, littered with dead trees.
"Out of hundreds of trees that we're looking at, maybe two or three of the 'ōhi'a trees still have leaves on them," says J.B. Friday, an extension forester with the University of Hawaii and one of scientists in the group. "It's heartbreaking for people who knew what this forest was 10 years ago."
'Ōhi'a covers about 865,000 acres statewide. Aerial surveys taken in January show the disease has now spread to more than 34,000 acres on the Big Island, more than doubling in the past two years. Some other things the researchers noted is that the annual death rate for 'ōhi'a trees on the island is 26 percent — so if it's not contained, it could decimate the forests in less than five years.
Using a small ax, Friday begins chopping at a dying tree, revealing signs that the fungus has taken hold.
"The fungus sometimes has a fruity smell that to me smells like bananas. That tree over there that we're looking at now, that you can see is turning brown, when we went inside and chopped on that, the symptoms are right there," he says.
In 2010, Friday started getting phone calls from landowners in the area, reporting 'ōhi'a trees dying on their property.
"We took some samples and didn't get anything unusual. But by 2013 it became apparent that something was spreading rapidly."
Friday called up his colleague Flint Hughes, a research ecologist with the U.S. Department of Agriculture's Forest Service.
"This forest was really a jewel of native diversity. It was perhaps the best example of a mature, 'ōhi'a dominated forest," Hughes says.
Hughes calls 'ōhi'a critical to maintaining Hawaii's watershed. Raindrops and condensation filter through the tree's leaves, keeping the ground well saturated. It also provides habitat and food for endangered native birds.
"This is our everything tree," he says. "It's the most wide spread, it's the foundational species for our forests. If we lose 'ōhi'a, it will transform our forests."
In addition to its environmental role, 'ōhi'a is also important culturally. Its wood was used to create tools and weapons, says University of Hawaii professor, Kalena Silva. And hula dancers often adorn themselves with its blossoms.
"I think the loss of 'ōhi'a lehua would almost be like losing a member of your family. It's that important. It has that much meaning," Silva says.
Plant pathologist Lisa Keith is leading the research on Rapid 'Ōhi'a Death, she works from Pacific Basin Agricultural Research Center's laboratory. For the past year, she's been studying tree samples and performing what she calls "CSI tree autopsies."
And what she's found isn't all grim. Keith says even in the most devastated areas, some trees are surviving.
"I think it's still hopeful that we will find ones that it's not an escapee, that it actually is natural resistance," she says. "We can then bank seed or propagate and replant. And that's some of the work for the future."
A more immediate concern is stopping the spread of the disease. Recent aerial surveys show the fungus has already devastated trees in tourist destinations like Hawaii Volcanoes National Park. Rapid 'Ōhi'a Death could spread to other islands, but that depends on Hawaii's success at containing it quickly.
Copyright 2016 Hawaii Public Radio