By Seana Walsh, Conservation Biologist and Dustin Wolkis, Seed Bank and Laboratory Manager
Ohia is the Hawaiian name for species in the genus Metrosideros. Ohia are the most abundant, ecologically important, and culturally significant plants in Hawaii. As a foundation species, forming the largest portion of the canopy in native wet and mesic forests, they provide food and shelter for many native animals, including our native forest birds and insects. Further, Ohia facilitate soil development, provide habitat for seedling establishment, and aid in replenishing our aquifers. Ohia are also culturally significant and prominent in many moolelo (stories), mele (songs), oli (chants), and are one of the kino lau (physical manifestations) for several Hawaiian deities.
In 2013, Hawaii Island residents became concerned when they began observing seemingly healthy ohia trees dying within a matter of weeks. This phenomenon was termed Rapid Ohia Death (ROD). Researchers have now identified that ROD is caused by two recently described species of Ceratocystis fungi previously unknown to science, C. lukuohia (“destroyer of ohia”) and C. huliohia (“changes the natural state of ohia”). Although trees can be infected with either fungal species for long periods of time, nutrient and water transport is eventually blocked. Once a tree shows symptoms of infection by C. lukuohia, all leaves turn brown and the tree is dead within weeks. Infection by C. huliohia is more localized, potentially affecting only parts of the tree.
ROD has affected over 75,000 acres of native ohia forest on Hawaii Island. In May of 2018, C. huliohia, the less aggressive of the two fungal pathogens, was confirmed on Kauai. When Ohia disappears from the landscape, habitat for other native plants and animals vanishes; non-native, invasive plant species, such as strawberry guava (Psidium cattleyanum), replace native forests.
To mitigate the spread of ROD throughout the archipelago, the State of Hawaii has implemented a quarantine that prohibits the transport of untreated Ohia wood from Hawaii Island. A committee of experts have formulated a ROD Strategic Response Plan which includes a statewide effort to collect and bank Ohia seeds from seed zones throughout Hawaii.
Seed zones are areas within which plant materials can be transferred with higher likelihood of survival in their new location. These zones are a crucial tool used to guide plant collections and reintroductions.
NTBG staff and the Kauai Island Botanist of the Hawaii State Department of Land and Natural Resources, Division of Forestry and Wildlife (DLNR, DOFAW) worked together to create seed zones for Kauai.
Based on climate and vegetation data, along with local knowledge of the environment, 10 unique zones were identified. Seed zones have helped guide landscape restoration projects across the continental United States. However, this approach to guide transfer of seeds has not been applied on Kauai, where the highly eroded island contains many different microclimates across relatively short distances. Although the impetus for creating seed zones was to guide current seed collections, banking, and future reintroductions with the potential for ROD to spread to Kauai, they have relevance for all native plant species occurring across the island.
In the winter of 2017, NTBG was awarded a grant from the Hawaiʻi Tourism Authority to help mitigate the potential for ROD to impact Kauai. Components of the grant-funded project, in which many NTBG staff are involved, include outreach and education through workshops, our visitor program, and social media and marketing.
This grant has supported coordinated efforts to collect, bank, and reciprocate seeds with Hawaii Seed Bank Partnership organizations of all four Metrosideros taxa from each of the 10 seed zones on Kauai. Throughout 2018, NTBG staff, interns, and volunteers embarked on approximately 30 collecting trips, half of which require helicopter flights to otherwise inaccessible locations. Collections were made from single individuals as well as from several individuals within a single population.
Individual plants were tagged using a “Population Reference Code” system standardized in the State of Hawaii. This unique plant ID system will ensure consistency and streamline future monitoring. Specifically, it will allow researchers, conservation biologists, and land managers to link individuals found to have ROD resistance or other measures of high fitness, back to the mother tree from which the seeds came.
The collecting goal for 2018 was from approximately 1,300 individual trees encompassing all four taxa spanning each seed zone in which they occur, totaling over six million seeds. A small portion of these seeds was sent to NTBG’s Conservation and Horticulture Center Nursery for immediate propagation for outreach, ex situ (“off-site”; outside their natural habitat) collections in our gardens, and in situ (“on-site”; in their natural habitat) restoration.
Most seeds were banked, as they are desiccation and freeze-tolerant and can, therefore, be stored using conventional methods (as opposed to seeds of species which are sensitive to desiccation and/or subfreezing temperatures, which require special storage conditions). After desiccation seeds are hermetically sealed and stored at -80°C.
Initial viability was determined for collections entering the NTBG Seed Bank and Laboratory, and viability of stored seeds will continue to be assessed at designated intervals throughout the lifetime of the collection. These data contribute to our understanding of seed longevity for each collection, and when taken as a whole, increases our knowledge at the species level. To mitigate against disaster striking any one storage facility, one-third of banked seeds are stored in the NTBG Seed Bank and Laboratory; one-third are stored on island at the Kauai DLNR, DOFAW Seed Bank; and one-third are stored off island on O‘ahu at the Harold L. Lyon Arboretum, Seed Conservation Laboratory.
These seeds will provide geographically and genetically appropriate plant material for restoration, testing for resistance to the disease, and other current and future research. This work is only possible by a coordinated effort between many NTBG staff, interns, and volunteers, as well as partner organizations working on all aspects of the project. By undertaking this project we are doing our part to perpetuate Ohia on Kauai.
You can help prevent the spread of Rapid Ohia Death by not moving Ohia wood; not transporting Ohia inter-island; sanitizing tools, gear, apparel and other equipment, and pressure washing vehicles before and after working in Ohia forests. For more information on ROD, visit rapidohiadeath.org.
 Foundation species are locally abundant, regionally common, and create conditions required by many other species.