Scientists uncover surprising findings in Big Island forest, 27 years after clear-cut

In 1985, a biopower company cut down and wood-chipped 900 acres of the 2,500-acre Ki’ula Forest, located in the eastern most portion of Hawaiʻi Island.

Pacific Southwest Research Station ecologist Flint Hughes and Conservation Biology Institute scientist Dennis Grossman recently published their findings on how the forest fared, 27 years after the clear-cut.

“I see this event as a tragedy, because of the destruction of part of the Ki’ula Forest. At the same time, it’s a story of hope for recovery, particularly for native ōhiʻa, a keystone species in Hawaiʻi,” Hughes said.

Ki’ula’s name, which means red flowering, comes from the 200-to-400-year-old crushed
lava rock where the forest mostly grows. About 1,300 feet in elevation, the forest provides a diverse native understory and habitat for birds, bats and other wildlife.

“Ki’ula is the best example of some of the last remaining lowland wet forest in Hawaiʻi. Throughout the Ki’ula Forest, it’s common to see 100-foot-high ʻōhiʻas,” Hughes said.

Hughes, Grossman and other scientists expected it would take a long time for the forest to recover, and ʻōhiʻa trees to regrow. Measuring the density or biomass of trees, researchers set up forest monitoring plots in three distinct sections – 11 in the clear-cut area, four in the mature forest; not clear-cut, and seven plots in clear-cut stands with invasive albizia. What they found surprised them.

In the clear-cut stands, they discovered a high density of ʻōhiʻa trees. Although smaller in stature than those in the uncut area, ōhiʻa trees dominated the landscape – with some larger trees measuring 20-25 centimeters in diameter. Also surprising to the researchers was finding a lot of native kōpiko and very little invasive strawberry guava. A member of the coffee family, kōpiko is endemic to Hawaiʻi.

Bordering the clear-cut, the mature forest fared the best with the densest number of ʻōhiʻa trees. In contrast, clear-cut stands inundated with invasive albizia were in the worst shape, with few ʻohiʻa trees making a comeback.

“We were surprised to see that after 27 years of secondary succession at these sites, we got more than half of the biomass back and that’s all in ʻōhiʻa. That’s a respectable rate of accumulation,” Hughes said.

Hughes concluded that ōhiʻa grew quickly, because of a combination of rich soil and the dispersal of seeds from the surrounding, mature forest. The studies also reinforced the need to remove invasive albizia, which prevents ʻōhiʻa from flourishing.

“These studies show ʻōhiʻa is resilient and can regrow quickly. Planting ʻōhiʻa in agricultural plantations can also help conserve this species, while providing habitat for wildlife that depend upon it,” Hughes said.