Preserving Our Prairies

ECOLOGY. Sprinkled in Western Washington's ocean of Douglas firs are islands of butterflies, wildflowers and knee-high grass - habitats threatened by development and the pernicious Scotch broom.

MIMA MOUNDS NATURAL HERITAGE PRESERVE, Thurston County - Butterflies spangle these grassy plains, their brilliance lighting a sun-washed, open landscape that is one of the rarest ecosystems in the country.

The prairies south of Puget Sound are a tiny remnant of the grasslands that used to cover the lowlands from Everett to Olympia.

While there used to be about 160,000 acres of prairies in the Puget Sound region, today only about 3,000 acres of native Puget prairie remain. And most of it is in fragments smaller than 100 acres.

There are many reasons why.

In wet years, Douglas fir trees take root in the normally droughty prairie soils and encroach on what should be an open landscape. Scotch broom, an invasive species, has packed some prairies full.

And then there's pavement, the most pernicious invader of prairies. These flat, well-drained sunny spots were among the first to go as the Puget Sound region urbanized. Much also has been lost to agricultural and suburban development.

Plants and animals that rely on prairie habitat are also in trouble.

There are about 200 species of butterflies in Washington, and 50 can be spotted in prairie environments. Nine of those 50 depend on prairie environments for food and nesting habitat.

The Washington Department of Fish and Wildlife has designated four of those nine prairie-dependent butterflies as candidates for listing as threatened or endangered, including the mardon skipper, the Puget blue, the Wulge checkerspot and valley silverspot.

Other rare animals dependent on prairie habitat include the western meadowlark, the Mazama pocket gopher and the streaked horned lark. Some species, including Sand Hill cranes and Western pond turtle, have already become extinct in the Puget prairies. The sharp-tailed snake, with its spike-like tail tip, hasn't been seen in the Puget prairies in 50 years and also might be gone.

A GEOLOGIC STORY TO TELL

But there are still some special, largely intact segments of prairie habitat left, mostly in publicly owned preserves and at Fort Lewis Army base. These prairies are among Washington's ancient landscapes, and they have a geologic story to tell.

The grassy areas were formed during the last ice age about 10,000 years ago. They, and the gravelly soils beneath them, are the handiwork of the great continental ice sheet squeezed by the Cascade and Olympic mountains into the Puget trough.

The glacier inched all the way from the Canadian border - where it was more than a mile thick - to its terminus south of Olympia.

As the glacier began to recede in the late Pleistocene, it left behind the cobble, gravel and silt composing the glacial outwash soils under much of Tacoma, Olympia and Tenino.

This geology is key to the open quality of Washington prairies: The droughty soils don't support lush growth of Douglas fir and other conifers.

Humans also have kept this land open for millennia: Indians burned the grasslands in summer and fall to simplify hunting and food gathering. They prized the prairie for the habitat it provided for camas bulbs, which they ate both fresh and dried.

Burning cleared the land of noxious weeds and tree seedlings, and stimulated grass growth. With the growth of human population, fire suppression has replaced controlled burns and natural fires, allowing weeds and trees to grow unchecked except during drought.

Some trees are native to the prairie landscape. Stout Garry oaks, the only native oak in Washington, are often found on the fringes. Ribbons of cottonwood or ash line some streams.

In the spring, a palette of wildflowers, including sunshine yellow balsam root, blue-purple prairie lupines and woolly sunflowers, dance in the new green grass. Yellow western buttercups, blue shooting stars, violets and deep purple camas flower cover the open sunny plains.

White-topped asters linger in the fall, lighting the golden, sun-burnt grass, which grows knee-high during the summer.

The cornerstone of these prairie grasslands, though, is Idaho fescue, or Festuca idahoensis, a native perennial bunch grass.

The Puget Sound bunch grass prairies are different from the waving, tall-grass prairies of the Midwest. The grasses on the latter feast on deep topsoil. Puget Sound prairies are rooted in shallow, gravelly soils and are found primarily in five counties: Grays Harbor, Thurston, Lewis, Mason and Pierce.

The prairie landscape is also home to one of the most enduring mysteries of Washington geology: the Mima Mounds.

This Natural Area Preserve, managed by the state Department of Natural Resources, still stumps geologists.

Mounds ranging up to 6 feet high and 30 feet in diameter are spaced in a close pattern across the landscape, giving it a popcorn pattern.

Everything from giant gophers to freezing and thawing after the retreat of the glaciers to earthquakes and erosion has been suggested as a cause. Nobody knows for sure.

The Nature Conservancy has been at the forefront of Washington prairie preservation for at least 20 years.

Patrick Dunn, prairie restoration ecologist with the Nature Conservancy, and teams of volunteers work with state and local government to care for prairie preserves throughout the Puget Sound region.

Prairies are high-maintenance landscapes. Left alone, the open vistas are quickly choked by Scotch broom and trees.

ATTACKING WITH WEEDWACKERS

The conservancy's Scotch-broom attack teams use everything from Weedwackers to hand loppers to keep Scotch broom at bay. Scotch broom seeds are viable as long as 70 years. On a summer day on the prairies, you can hear its seed pods pop in the heat, scattering the next generation across the landscape. Cut Scotch broom back in the spring, and it will re-sprout from the base stronger than ever within one growing season.

Dunn, of the Nature Conservancy, has mowed Scotch broom 14 feet high and says it can take a concerted attack of up to three seasons to kill it.

"I take them all personally," Dunn said of the stubborn plant.

After five years of work, the conservancy has helped reclaim more than 800 acres of prairie at Glacial Heritage Preserve south of Olympia.

Some prairie landscape also has been deliberately burned to clear and revive it.

In addition to removing invasive plants and trees, the conservancy is replanting thousands of native plants, including Idaho fescue, lupines, purple asters and Oregon sunshine, a yellow wildflower.

Staffers from the conservancy and biologists from the state Department of Fish and Wildlife also are monitoring butterfly populations at three prairies targeted for restoration.

At Mima Mounds preserve on a recent sunny day, a profusion of butterflies tears across vast, bright space, and clings to open blossoms.

As it drinks nectar from a purple thistle bloom, a Great Spangled Frittilary slowly folds and unfolds its velvety black wings spotted with silver.

The dark color has function: It helps absorb solar heat to warm the butterfly so it can work.

It's a big butterfly, with a palm-sized wingspan. It clings to the tossing thistle, bucking in the breeze.

State scientists are studying these prairies to determine which plants the butterflies depend on, and how they use them.

It's necessary work: Some butterflies don't migrate. If they lose their prairie habitat, they lose their home and food supply.

"Their dependence on these plants is absolute," said David Hays, a biologist at Fish and Wildlife.

Preservation of the Puget prairies is important for people, too.

"These habitats are important conservationwise, but they are also very beautiful," Dunn said. "People get used to thinking of open spaces only as parking lots."

Lynda Mapes' phone message number is 206-464-2736. Her e-mail address is lmapes@seattletimes.com