A deadly fungus threatens the native ʻōhiʻa tree and the future of the Hawaiian forest.
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"What replaces 'ohi'a that die, at least in Puna, is invasive weeds -- and that's the end of the native forest. "
Forester, University of Hawaii College of Tropical Agriculture
By Jan Tenbruggencate
The iconic ʻōhiʻa tree is under siege on Hawai‘i Island from a mysterious fungal attack that kills big trees and small, weak and strong, on new lava and old soil.
Foresters, pathologists, land managers and government agencies are doing all they can to stop or at least slow its spread. But so far, there has been no breakthrough in efforts to contain it. In the five years since it was first reported in Puna, the disease has killed more than 100,000 trees on Hawai‘i Island and affected 55,000 acres. Foresters say it poses a mortal threat to the Hawaiian forest.
“We are very, very concerned about this disease and its impact on our native forest,” said Flint Hughes, research ecologist with the U.S. Forest Service’s Institute of Pacific Islands Forestry.
“It’s a huge threat. What replaces ʻōhiʻa that die, at least in Puna, is invasive weeds — and that could be the end of the native forest,” added J.B. Friday, a forester with the University of Hawaii’s College of Tropical Agriculture and Human Resources.
Mother of the Hawaiian Forest
ʻŌhiʻa is considered the mother of the Hawaiian forest and carries immense significance in Hawaiian culture. Half of the native trees on the Big Island are ʻōhiʻa. Native birds live in them and feed on them. Tree snails graze on their leaves. Mosses find space between their surface roots. Their canopy protects the innumerable smaller trees and native shrubs, creating the watershed that feeds our perennial streams and recharges groundwater.
“The word ʻohi means to gather,” said Sam ʻOhu Gon, the Conservancy’s Hawai‘i senior scientist and cultural advisor. “The ability of ʻōhiʻa to gather water from passing clouds and deliver it into the ground is one of the most important ecosystem services it provides for all of us.”
Scientists have classified the disease as a type of wilt and named it rapid ʻōhiʻa death. It is characterized by a sudden yellowing and browning of the leaves on entire branch systems or the whole tree.
The culprit is a previously unknown form of the fungus, Ceratocystis fimbriata. The strain probably arrived from outside Hawaiʻi, said Lisa Keith, a research plant pathologist with the USDA Agricultural Research Service.
The fungus appears to kill trees by blocking the vessels that carry water up the tree. An infected ʻōhiʻa will have black streaks in its normally pink wood. It’s not yet clear how the fungus gets into the tree. A wound, like a broken branch, a recent pruning or even an insect borehole, may be involved.
“Right now, there is no known way to save a tree once it’s infected,” said Friday.
Establishing a Quarantine
To prevent spread to new trees, forests and islands, foresters are emphasizing biosecurity. A key is sanitation: Don’t move wood, soil or any ʻōhiʻa trees or plant parts. Use alcohol or bleach to clean any boots, chain saws, cars and other tools and heavy equipment used in any forested area.
The State Department of Agriculture recently established a quarantine to prevent the disease from spreading to other islands. Any interisland movement of ʻōhiʻa wood, plants or plant parts from Hawai‘i Island requires a permit from the department. As of February, the quarantine also includes soil.
Meanwhile, researchers are trying to determine whether some strains of ʻōhiʻa may be resistant:
“The way it’s manifesting, it doesn’t wipe out all the trees in a single area. It doesn’t hit every single tree,” said Trae Menard, the Conservancy’s Hawaiʻi director of forest conservation.
As scientists learn more, they are quickly sharing best practices.
“We need to do everything we can to prevent the spread of this disease and save the native forest,” said Keith.