Conservationists and small timber harvesters have replanted koa on thousands of acres on the Big Island and Maui, increasingly fencing out the cattle, pigs and goats that forage on koa bark and seedlings.

They hope replanting the slow-growing trees can help restore the feeding and nesting grounds of endangered native forest birds and quench demand for valuable koa timber, with a scarcity and a lustrous grain that rank it among the world's most expensive woods. A tree can take 40 years to mature.

"Koa is a key species in the ecology of the Hawaiian forests," said Craig Elevitch, co-author of the book "Growing Koa." "It's also one of the most important trees to human culture and economy in Hawai'i."

Koa trees are slowly recovering on the slopes of Mauna Kea at the Hakalau Forest National Wildlife Refuge, which was set aside specifically for forest birds.

Since the refuge opened in 1985, volunteers and refuge officials have planted more than 271,000 koa trees on about 5,000 acres, with survival rates averaging 70 percent, said Baron Horiuchi. a horticulturist for the U.S. Fish and Wildlife Service.

The birds need koa to shelter the smaller plants they feed on, such as the red splayed blossoms of the ohia lehua, giant Hawaiian raspberries and marble-sized red 'ohelo berries. A spreading koa canopy protects seedlings and smaller plants from cold upland temperatures, which can dip into the 20s during winter on Mauna Kea.

"Koa is a pioneering tree," Horiuchi said. "It leads the way for the rest of the forest."

In many parts of the refuge, koa trees are the only native plants growing among the introduced species of weeds and grass. The branches on many of the larger trees at Hakalau grow in a serpentine network, an illustration of the name for this area, which means "many perches" in Hawaiian.

"The point is not to grow them straight for timber or canoe logs. They are to grow as a canopy and a bird habitat," Horiuchi said. "I always joke with people that this place is 'for the birds,' but it's true."

Private koa farmers prefer the tall, straight-growing trees. They hope to harvest the semi-hard wood, which ranges in color from blond to red or dark brown, for furniture, bowls, musical instruments and traditional Hawaiian seafaring canoes.

Umikoa Ranch on the Big Island, in partnership with state land officials, reforested 800 acres with koa trees between 1980 and 2004.

David Matsuura, managing steward at the 2,000-acre ranch, said some of the trees planted about 15 years ago have already reached large diameters, although he isn't sure about the quality of the wood.

"That's the problem with koa. It's a very long-term crop," Matsuura said. "I'm gonna be pretty old and gray before most of our koa is actually harvested."

Ranch managers said the trees have already helped re-establish native plants and animals, including eight endangered Hawaiian ducks. The return of koa has also increased water sources at Umikoa, where the sickle-shaped koa stems draw fog and moisture into the watershed.

"Our main goal is the integration of conservation and agriculture," Matsuura said. "It's not the same as clear-cutting."

But profit is also a goal for koa farmers, who are gambling over the long term on a product that commands premium prices. At Hawaiian Koa Furniture in Honolulu, a 54-inch round koa table sells for $8,000.

The bulk of the koa market is driven by Hawai'i residents, who are the world's biggest consumers of richly varnished koa products.