In 2012, Robert Hauff and other researchers noticed something unusual about the ohia trees they were studying in Puna. The canopy of the trees seemed to be dying back at an alarming rate. Residents had also been reporting similar observations in the area.
It would be several more years until scientists were able to identify and put a name to the cause: Rapid Ohia Death, a disease caused by a type of fungus that infects the trees via open wounds. It inhibits the trees’ ability to circulate water, leading to their death over the course of just months.
Now, over a decade later, Hauff, who is the state protection forester with the Department of Land and Natural Resources, said efforts are ongoing to better understand and address ROD. While it has also been detected in different forms on other islands, it is most prevalent on the Big Island where it is estimated to have killed over 1 million ohia trees and counting.
“We are continuing to see areas highly impacted by Rapid Ohia Death, a couple of areas that come to mind are Laupahoehoe and Ka‘u,” Hauff said. “The amount of tree mortality that we see there with our monitoring is really heartbreaking to see some of our nicest ohia forests in the state being impacted in this way.”
DLNR, in partnership with other agencies and organizations, recently published a new ROD strategic response plan, which provides an overview of what has been learned about the disease, current tools to manage it, and areas in need of additional research to be able to better protect the trees.
Endemic to Hawaii, meaning they are not naturally found anywhere else on Earth, ohia trees are essential to Hawaiian ecosystems, Hauff said.
“It’s a big concern for our forests on Hawaii Island. It’s the backbone of our native forests, habitat for our endangered forest birds,” he said, adding that the trees also play a role in maintaining healthy watersheds and are culturally important to Native Hawaiians.
Ryan Perroy is a professor at the University of Hawaii at Hilo who is also the director of the university’s spatial data analysis research lab and has been studying ROD using drones and satellite imagery.
“What my group has been focused on is trying to map out the mortality,” he said. “Early on, we were trying to be able to identify new outbreaks, and that’s certainly also still an important thing. And then once there is mortality happening, we’re trying to characterize, basically, the spatio-temporal trends.”
The lab recently has received a $2.25 million grant from the National Oceanic and Atmospheric Administration to help fund this work through 2028.
“We’ve learned a lot so far, and then I think we’ve got some management tools under our belt that we didn’t before, but there are still some unanswered questions,” he said. “So, as part of that, trying to understand those additional questions, that’s where some of these federal funds have come in.”
Among the discoveries that researchers like Perroy have contributed to is the role that animals, specifically hoofed ungulates like pigs, play in spreading ROD. He said his lab has been able to use its imagery to compare ohia forests where these animals were present with fenced areas where they were not, and noticed a dramatic difference.
“Where the animals are there, or if the animals break into a fence line where they hadn’t been before, you see much higher mortality,” he said.
While he said more research needs to be done, the higher mortality is likely due, at least in part, to the animals wounding the trees and opening them up to infection from ROD.
J.B. Friday, extension forester for the University of Hawaii at Manoa, has also been studying ROD since the early days of its detection on the island. In addition to identifying the cause of the disease and better understanding how it spreads, he said another helpful discovery is that some trees seem to be resistant to the fungus.
“I think we definitely can say there is resistance to ROD in the natural ohia populations,” he said. “What we don’t know — and it’s going to be a few years more before we start finding out — is if it can be inherited. If a mother tree is resistant, do the seedlings, the seeds taken from that tree grow into resistant trees too, or not? Some things get passed down more than others. We have to do that kind of work still, but there’s resistance out there that we can work with, so that’s encouraging.”
The state recently awarded $82,999 to the Hilo-based nonprofit Akaka Foundation for Tropical Forests to continue work on developing disease-resistant ohia.
In addition to ungulates, beetles — specifically invasive ambrosia beetles — have also been found to facilitate the spread of ROD, according to Kylle Roy, a forest entomologist with the U.S. Forest Service. When these beetles burrow into infected ohia trees, they release a sawdust-like substance, called frass, containing the ROD fungus that can then be spread to other trees.
In response, she has been working on deploying a beetle repellent that recently hit the market in Hawaii. Called Specialized Pheromone and Lure Application Technology Verbenone, or SPLAT Verb for short, it is essentially a biodegradable paste that can be applied to trees and deter beetles from burrowing there.
She said it is especially valuable in preventing a ROD outbreak in the early stages.
“When you have a new ROD outbreak, you can treat a ROD tree and then also treat healthy trees around it to prevent the spread of ROD from the ROD tree to the healthy trees,” she said.
Roy was also involved in the development of the ROD strategic response plan and, while she is excited about the potential of SPLAT Verb to stem the spread of ROD, she agrees with other researchers that more tools and resources are needed, especially when it comes to detecting the presence of the fungus.
“There’s really a need for early detection, because by the time we can see that a tree has ROD, it’s too late to try to treat it with a fungicide or something,” she said.
She plans to keep working on the issue along with other researchers like Hauff, Perroy and Friday from around the island, as well as the state, nation and globe who share the common goal of protecting ohia forests.
“The vision is for just healthy, functioning forests and honeycreepers singing, just like the way it should be,” said Perroy, the UH Hilo researcher. “That’s really what we’re all trying to get to.”
Email Grace Inez Adams at grace.adams@hawaiitribune-herald.com.
