In 2010, residents in Puna began reporting an alarming observation: across the community, large swaths of ʻōhiʻa trees were dying. Within days to weeks a seemingly healthy tree would brown and die. The cause was at first unknown, and the phenomena came to be known as Rapid ʻŌhiʻa Death (ROD). Hundreds of samples were taken from trees and analyzed, and scientists in Hawaiʻi worked closely with specialists around the world to zero in on the culprit. By 2015, they had narrowed the identification down to Ceratocystis fungus, and by 2018 found that it was not one but two species of Ceratocystis fungi that caused ROD. Both were new to science, having never been found before, and were given Hawaiian names: C. lukuohia (causes systemic tree death, very aggressive) and C. huliohia (causes a canker disease, less virulent).
ʻŌhiʻa serves as a keystone species of Hawaiian forests, maintaining healthy watersheds and providing habitat for native flora and fauna. For those trying to preserve the remaining habitat and the functions of our life-supporting ecosystems, a potential loss of ohia meant profound negative impacts. A large working group consisting of dozens of individuals from agencies, universities, and non-profits came together to learn more about ROD and how to respond to it. As part of the working group, BIISC formed a rapid ʻōhiʻa death early detection/rapid response (EDRR) team to actively monitor and manage the spread of ROD in high priority areas on Hawaiʻi Island (Hāmākua, Kohala, and North Kohala), finding new detections of ROD and providing feedback to scientists on management efforts. Bill Buckley, BIISC’s Forest Response Coordinator, leads a crew of six ROD-EDRR technicians.
“Our crew performs quarterly aerial surveys by helicopter-two island-wide surveys and two surveys in North Hawaiʻi – to gain a clearer understanding of the changing forest canopy,” says Buckley. Using digital mobile sketch mapping technology, BIISC technicians map the forest canopy and identify suspect ROD trees from the air. As of October 2018, nearly 135,000 acres of ʻōhiʻa forest on Hawai‘i island showed some signs of the disease.
Once suspect trees are identified by helicopter, the team follows up with drone surveys to obtain accurate GPS coordinates of the area. Field work transitions from the air to the ground as the crew navigates to trees of interest to collect samples. ROD technician Kristen Hofer, who has been with the team since its formation, explains, “We use a standardized method developed by ROD researchers, that is used on other islands as well. First, collect wood chips with a hatchet, next, collect wood shavings using a drill, and finally, apply a pruning seal to collection site. The seal doesn’t prevent insects from attacking, but it does prevent the fungus from sporulating from the wound.” The samples are then submitted to Dr. Lisa Keithʻs USDA-PBARC lab in Hilo for DNA analysis. “If we are camping in a remote area and need to make sampling and management decisions quickly, we use our lab-in-a-suitcase technology, which gives us results in just a few hours,” says Hofer.
Rapid Response: Management
Once a tree has tested positive for ROD, our team can begin to make informed management decisions. Researchers have recently confirmed that ambrosia beetles play a role in the spread of rapid ʻōhiʻa death. These tiny beetles, attracted to dead and dying trees, burrow into infected wood and produce frass (tiny amounts of sawdust) that are laden with fungal spores and then carried in the wind or in soil. In order to reduce beetle activity and the amount of frass produced in the environment, the crew may cut infected trees down and cover them with tarps. However, this decision must be carefully considered. If felling a tree has the potential to damage living ʻōhiʻa nearby, it may be better to leave the tree standing than to risk wounding healthy trees and providing a possible entry point for ROD. Applying an insecticide to prevent beetle activity in wood piles or standing dead trees is another potential option that is currently being investigated.
The ROD-EDRR team at BIISC also trains other conservation agencies and land managers in Hawaiʻi on proper early detection and rapid response methods for ROD. To date, we have hosted multiple trainings here on Hawaiʻi Island for groups from Maui Nui and Oʻahu and we have also traveled to Kaua’i to train crews.