South Sound residents don’t have to visit Washington’s old-growth rain forests to get a glimpse of the state’s living history. It’s in the lustrous leaves and rugged branches of surviving Oregon white oaks, which once dominated South Sound prairies and still loom over some neighborhoods in Tacoma, Lakewood, Parkland and points south.

“People don’t realize how long-lived they are,” said Connie Harrington, an Olympia-based forestry researcher who since 1999 has led a team of U.S. Forest Service scientists studying Washington’s only native oaks.

Oregon white oaks can live 500 years or more, given the right circumstances. So it’s possible that some of the South Sound’s larger specimens sprouted before explorers such as Lt. Charles Wilkes entered Puget Sound in 1840.

Historically, Oregon white oak habitat ranged from British Columbia – where they are commonly called Garry oaks – to California. But the trees now occupy less than 1 percent of the area where they once were concentrated.

“It’s incredible how much oak woodland has been lost,” said Robin Dobson, a U.S. Forest Service botanist based in Hood River, Ore.

The reason? In urban areas, people have cut oaks to make way for roads, homes and businesses. On commercial timberlands, more valuable conifers have supplanted oaks. Elsewhere, oaks have died or are slowly dying because they can’t compete with larger and more vigorous Douglas firs.

But as Harrington and her colleagues have found, oaks thrive if given a chance. All that’s needed is to take them out of the dark.

“Oak trees love the sun,” said David Anderson, a state Fish and Wildlife biologist based in Klickitat County, which at 195,000 acres has the state’s largest concentration of Oregon white oaks. “They really don’t like shade.”

Biologists cite the oaks’ importance to scores of species, perhaps most famously the vanishing Western gray squirrel. Its home on Fort Lewis includes 3,600 acres of oaks in areas that could be divided by the proposed cross-base highway.

The Army began trying to save oaks about 10 years ago by cutting firs that blocked the sun and selling the timber, said Jeff Foster, the post ecologist. Harrington’s group has based much of its study on Fort Lewis, which provided several hundred thousand dollars in support, Foster said. The results have validated the post’s oak conservation efforts.

“Even if these trees are pretty far gone, it looks like they can recover,” Foster said.

Oregon white oaks are vital to wildlife as a source of food and a refuge for insects, birds and mammals.

Squirrels use oak woodlands like an aerial highway, a network of branches through which they race. They also rear their young in the trees. When oak limbs fall, cavity-nesting birds bore into the resulting hollows.

Oak acorns may be even more important to wildlife than any other food source, scientists have said. Of course, squirrels love the nuts. And in winter, deer paw the ground to find them.

“Everybody likes the acorns,” Harrington said. “Woodpeckers, jays, band-tailed pigeons.”

Even oak foliage is important. As browse for deer and elk, it provides as much protein as alfalfa, scientists say. Oaks also attract insects. For example, the larvae of the Propertius duskywing, a brown butterfly, hibernate in the leaves.

Before white settlement, American Indians periodically burned South Sound prairies and other valleys. The ground-level fires kept conifers at bay and encouraged the growth of comparatively fire-resistant oaks. This was important because tribes subsisted in part on the acorns and associated prairie vegetation, such as the bulbs of camas flowers.

On Fort Lewis, periodic fires in the artillery-impact areas achieve similar ends, as do controlled burns on protected lands such as Thurston County’s Glacial Heritage Preserve, near Littlerock. The Nature Conservancy manages the 1,100 acres along the Black River to save the oaks and other increasingly rare prairie grasses and flowers.

Carri Marschner, Nature Conservancy land steward, has welcomed Harrington’s help. She was happy to permit a Forest Service research crew to practice chain saw skills at the preserve by cutting down firs, which virtually imprisoned the oaks in shade.

“We definitely want to get all these mature oaks freed,” she said as she watched crew members work.

Harrington’s team already has proved that oaks benefit from “oak release” treatments. “When you release individual trees, you give them a new lease on life,” Harrington said.

Recently, she and other researchers have begun more detailed oak studies, to determine how the trees respond to different circumstances, such as soil moisture.

Although mature oaks can reach 60 or 80 feet in height, they grow slowly.

“It can take 100 or more years to get a large oak tree,” Harrington said.

Shape is important, she said, especially when it comes to propagation. Scientific results are preliminary, but it appears that the trees that produce the most acorns are the ones with the biggest crowns.

When Harrington describes oaks, she talks about vases and mushrooms. The words depict the profiles of mature trees. The mushroom shape embodies the oak ideal, the kind of tree that typically stood out on savannahs. The vase, now more common, suggests a history of crowding that limited growth.

Now, with 90 percent of remaining oaks in private ownership, Harrington is hoping that landowners will take action. As attractive as mixed stands of oaks and evergreens may be, fast-growing, tall firs can kill slow-growing oaks with shade.

“Although (landowners) might like the mixture now, if they don’t take some action it will become all conifer,” Harrington said. “The time to benefit the oaks is when they still have good crowns. You don’t want to wait until they have a lot of branches die.”

Susan Gordon: 253-597-8756