There is hope for reestablishment of native and climate-friendly ʻōhiʻa trees, study says

Federal and university researchers released a new study that provides “encouragement and guidance” for land managers to reestablish native ʻōhiʻa trees wiped out by a fungal disease or impacted by volcanic activity and wild fires. 

In the academic paper, Aboveground carbon accumulation by second-growth forests after deforestation in Hawai‘i published by the Ecological Society of America, researchers studied how carbon accumulates after lava flows, fire, disease and other disturbances in the native ʻōhiʻa compared to invasive species Albizia and strawberry guava.

The authors write the opportunity to understand and document aboveground forest carbon accumulation presented itself in the mid-1980s when portions of an intact, mature native lowland rainforest in the Puna District of Hawai‘i Island were cut to the ground and bulldozed. 

“These actions created extensive areas of exposed, highly disturbed lava fields across most of the clearcut region,” the study said.

Subsequent long-term monitoring of secondary tree succession showed widespread recruitment and growth of native ʻōhiʻa seedlings and also invasive strawberry guava, which is considered a profound threat to native Hawaiian forests. It has displaced native species across hundreds of thousands of acres.

Ecological succession is the process of change in a species structure of an ecological community over time. 

One of the researchers’ primary questions: “After several decades of succession since disturbance, to what degree have second-growth forests in clearcut areas accumulated carbon mass relative to adjacent, intact, mature primary forests?”  

More broadly the scientists wanted to learn the extent to which Hawai‘i’s dominant native tree, ʻōhiʻa, will be a viable candidate for reforestation efforts in the wake of stand-level kill-off induced by the fungal disease, Rapid ʻŌhiʻa Death, and how ʻōhiʻa dominated forests may help combat climate change by increasing forest carbon capture across the Hawaiian Archipelago. 

The lead author of the study, USDA-Forest Service research ecologist Flint Hughes, explained the surprising and heartening result: “Not only are mature ʻōhiʻa forests capable of storing as much carbon in their living biomass as big tropical rainforests elsewhere in the world, second-growth ʻōhiʻa forests recovering from disturbances, such as clearcutting, grow every bit as fast as highly productive second-growth forests in Latin America, Asia or Africa”.  

However, Hughes cautioned that the rapid carbon accumulation of second growth ʻōhiʻa forests only occurred where invasive, non-native trees like strawberry guava and Albizia were not present.

“Given those results, it’s clear that non-native weed management is essential to the reestablishment and continued health of our ʻōhiʻa forests,” he said.  

The recent study confirmed previous studies that showed ʻōhiʻa stands could replace themselves quickly, if non-native plant invasions don’t disrupt their establishment and development. 

On Hawai‘i Island, there are an estimated 290 million mature ʻōhiʻa. Collectively, they are an order of magnitude more numerous than any other native tree species. 

David Smith, Administrator for the DLNR Division of Forestry and Wildlife (DOFAW) said: “This is invaluable information in helping guide us to make restoration and recovery decisions for ʻōhiʻa-dominated forests that have seen the devastating impacts of the fungal disease. It supports our long-held notion that native species are best for various reasons, not the least of which being valuable in capturing carbon from the atmosphere, as we investigate and consider all tools to combat climate change.” 

The study was conducted by researchers with the Institute of Pacific Islands Forestry, US Forest Service Pacific Southwest Research Station, California Strategic Growth Council, University of Hawai‘i at Mānoa and Brigham Young University.