Seeds lessen impact of forest burn
By Jan TenBruggencate
Advertiser Science Writer
VOLCANO, Hawai'i — The spread of alien grasses has made the 'ohi'a forests on the Kilauea volcano more susceptible to fire, and is hurting native ecosystems.
National Park Service photo
Forests once dense with native plants, birds and insects are being converted to tracts of weedy trees and grassland where species found only in Hawai'i are on the decline.
Sierra Club volunteers spread mamane and 'a'ali'i seeds in August 2000, a month after a 1,000-acre fire at the Mauna Loa Strip Road in Volcano. The native plants resist fire and may help prevent takeover by introduced species.
National Park Service biologists have begun trying to use a special class of native plants to fight the trend, identifying species that are most resistant to fire and planting them in hundreds of pockets within burned zones.
The results are becoming apparent. Among the alien grasses grow the shiny yellow-green leaves of 'a'ali'i, the frosted green saplings of koa, the compound leaves of the mamane tree, and the low, viney 'ulei.
"These species are present in 'ohi'a woodlands, but are perhaps not as prevalent as they once were," said Hawai'i Volcanoes National Park biologist Rhonda Loh.
It is hard to lessen the impact of alien grasses. Clumping species such as broomsedge and beardgrass spread readily, provide dry tinder and bounce back quickly after a fire, often far faster than native species.
"They create a continuous fuel bed of fine fuels that can dry out quickly," Loh said.
"Before, fire was not a very frequent occurrence in the 'ohi'a woodlands. Until the 1960s, the average size of fires was about a half-acre. Now fires can be as much as 1,000 acres, and some are bigger," Loh said.
Before humans arrived, volcano country had little fuel on the ground, so regular lava flows seldom created large burns. As a result, Hawaiian plants did not adapt to regular burning.
Since 1993, the park service has been conducting test burns and studying regeneration of native species, either through resprouting or from seeds that survive the burns.
They found two dominant 'ohi'a woodland species — the big 'ohi'a trees and pukiawe shrub — are sensitive to fire and don't readily come back afterward. But some plants respond fairly well, such as koa, mamane and 'iliahi (sandalwood) trees and the shrubs 'a'ali'i, 'ohelo and 'ulei, along with an upland 'akia.
A June 30, 2000, wildfire that burned more than 1,000 acres gave park staff a chance to put their research to work.
The fire ignited in an area saddling the Mauna Loa Strip Road where brooms-edge infested the 'ohi'a woodland. The researchers diverted plants that were to go to other plantings and collected seeds. With the help of Sierra Club and other volunteers, they began planting native fire-tolerant species and broadcasting seeds.
The idea was to get a population of native fire-tolerant species in place on the blackened burn site so they could begin spreading. The researchers established planting sites at 800 locations in the burn area, each with two to 60 plants.
The mix of plants may not closely match the regions' original communities, but does include many of the original species.
"We're trying to preserve our natural areas as much as possible," Loh said.
The theory assumes that after a fire, more than the fire-resistant alien grasses will come back. Ultimately, the fire-resistant plants may help convert the area from one that readily burns to one that doesn't, opening the door to replant plants that are not tolerant of fire.
