Pine trees may help contain, kill bush on Big Island

By Kevin Dayton
Advertiser Big Island Bureau

Conservationists are planting pine trees on Mauna Kea in an attempt to create a living "corral" to isolate and contain thousands of acres of gorse on the mountain.

The prickly gorse bush, which is classified by the state as a noxious plant, has taken over about 5,000 acres of Hawaiian Home Lands on Mauna Kea, and is creeping down toward Hilo along the Wailuku River and other stream channels, said Mike Robinson, forestry and natural resources agent for the state Department of Hawaiian Home Lands.

Parker Ranch, which leased those Hawaiian Home Lands until earlier this year, has tried aerial and ground herbicide spraying as well as burning to control the bushes.

Scientists even released a fungus at Humu'ula on Mauna Kea's southern slope that they hoped would attack the gorse and help kill it off, but the fungus died instead.

The latest effort to stop the advance of gorse involves planting sugi pine trees, a thick variety of pine that casts so dark a shadow that few plants can survive under it.

Gorse needs light, and a test planting of pine trees in Olinda, Maui, effectively halted new growth of gorse, Robinson said.

Experts hope the trees will create a natural perimeter that walls off the areas of Humu'ula that are most thick with gorse. State officials can then use other means to attack scattered patches of the plant elsewhere on the mountain.

"Hopefully we wake up in about 15 or 20 years and we have this nice perimeter planting of sugi pine that's shading out the gorse, and there's no gorse outside the corral of sugi," Robinson said.

Once the gorse is contained, Hawaiian Homes can focus on eradicating the gorse inside the pine perimeter, Robinson said. The thickest areas of gorse infestation today are between the Pu'u O'o area and the Hakalau Forest National Wildlife Refuge, he said.

Gorse plants have bright green thorns and yellow clusters of flowers when they are young. Older plants grow brown, and form thickets up to 15 feet high.

The sugi project involves planting about 320 acres of pine in a strip about 250 feet wide that will extend around 5,000 acres to 6,000 acres on the mountain. That works out to about 140,000 sugi seedlings.

So far Hawaiian Homes has spent about $20,000 on site preparation and tree planting, and has planted about 30 acres of trees, Robinson said. He predicted the department will plant another 50 acres a year over the next seven years until the perimeter is complete.

At the same time, Parker Ranch is spending about $100,000 a year testing other methods of gorse control and eradication ranging from spraying and burning to unleashing moss and spiders to try to kill gorse, said Brandi Beaudet, land resources and facilities manager for Parker Ranch.

Gorse is native to Europe, and was at times used as a living fence because the thick and thorny bushes could effectively contain animals. It arrived in Hawai'i in the 1920s, possibly imported accidentally in feed or in the wool of sheep imported from New Zealand, Robinson said.

Robinson, a longtime advocate of various forestry industries on the Big Island, said an important side benefit of the sugi pine project is that the wood is useful for woodworking. Sugi has a pleasant smell, and was traditionally been used to build temples in Japan, he said.

Reach Kevin Dayton at kdayton@honoluluadvertiser.com or (808) 935-3916.