Rapid ʻŌhiʻa Death Response
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.
Our crew performs regular aerial surveys by helicopter to gain a clearer understanding of the changing forest canopy. Using digital mobile sketch mapping technology, BIISC technicians map the forest canopy and identify suspect ROD trees from the air.
Once suspect trees are identified by helicopter, the team follows up with drone surveys to obtain accurate GPS coordinates of the area. Fieldwork transitions from the air to the ground as the crew navigates to trees of interest to collect samples. We use a standardized method developed by ROD researchers and applied statewide: first, collect wood chips with a hatchet, next, collect wood shavings using a drill, and finally, apply a pruning seal to the 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.
Rapid Response: Management
If 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 to prevent blowing of frass high on the wind. However, 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. All management decisions are made on a case-by-case basis. Currently, our team is collaborating with PBARC researchers to test the use of insecticides on felled trees to prevent beetle activity.
Collaboration is key
The ROD-EDRR team is instrumental in helping researchers gather data in the field. The team at BIISC also trains other conservation agencies and land managers in Hawaiʻi on proper early detection and rapid response methods for ROD, and have hosted multiple trainings here on Hawaiʻi Island for groups from Maui Nui and Oʻahu. Our ROD EDRR crew has also traveled to Kaua’i to train response crews in the field.