Friends and Fire: How Humans Shaped Oak Prairies

Oak prairies are home to increasingly rare sights in Washington.

Fifteen thousand years ago, the Vashon ice sheet began its melting retreat, depositing a plain of gravely outwash that underlies the prairies of South Sound. Over time the rocks broke down and organic matter accumulated, resulting in the quick-drying, nutrient-poor soil we have today. This soil defines the prairie ecosystem. It discourages all but the most nutritionally undemanding of trees and encourages a unique suite of relatively short grasses and wildflowers that can tolerate such conditions. Garry oak (Quercus garryana), Washington’s only native oak, thrives on the prairie. In an oak savanna, the trees grow far apart from each other. The sky is open. But without human intervention, these ecosystems would become a dense woodland canopy.

The human touch

One of the most unique qualities of the oak prairie ecosystem is that people are responsible for its very existence. Without the stewardship of Native Americans, who preserved this landscape with the use of frequent, low-intensity fires over many thousands of years, we would not have oak prairies in Washington at all. They set fire to the prairies to burn off unwanted woody vegetation and clear excessive thatch and moss that might suppress more utilitarian plants.

This burn regimen prevented fuel from building up, keeping wildfires relatively cool compared to the super-hot devastating forest fires we see today elsewhere in the state. It also provided medicine and food, such as the sweet, protein-rich bulb of the camas flower. Older oaks survived these fires and their seedlings fared well in the absence of heavy duff and sod. Native Americans ate the acorns—roasted, sundried, and raw—in soups, breads, and pancakes.

One of the most unique qualities of the oak prairie ecosystem is that people are responsible for its very existence.

Today’s challenges are not so much human as they are natural. Conifer forest is encroaching. Like the Garry oak, the dominant Douglas-fir doesn’t ask much from the soil. This diet, in combination with a fondness for sun, makes Doug-fir the biggest challenge to maintaining prairie and oak savanna. The tribes are working in partnership with Joint Base Lewis–McChord and organizations like Forterra to continue to steward these lands. Together, their ongoing restoration and management practices are preventing the prairies from reverting to forests in the next 500 to 1,000 years.

Conserving oak prairies

Forterra owns 25 acres of prairie in smaller parcels that buffer the prairies of Joint Base Lewis–McChord from greater Tacoma. At this size, they cannot offer meaningful habitat for endangered species. However, they are open to the public year-round and offer a taste of this special ecosystem for visitors. Forterra’s Schibig-Lakeview Nature Preserve has an 11-acre oak savanna with trees as old as 300 years.

Joint Base Lewis–McChord burns thousands of acres a year because, as federal land, it is exempt from clean air standards. As Forterra is not permitted for prescribed burning, we rely on the more labor-intensive manual removal of invasive species, along with judicious application of herbicide and the planting of native flowers and grasses.

With a grant from the Chambers-Clover Creek Watershed Council, Forterra is conducting research at Schibig to determine the most effective means of prairie restoration. We have set up five test plots, each subjected to a different treatment for the removal of invasive grasses, such as mowing or covering the ground with black plastic tarp. We then plant native flower and grass plugs and finally over-seed with native species. We’re still waiting to see what the final results will be, but we are hopeful that they will yield valuable lessons for prairie stewardship throughout the entire Pacific Northwest.

Support Oak Prairies

Blooms, refuge, and majesty

There are two weeks in and around Mother’s Day when the prairies and oak savannas of South Puget Sound are flush with wildflowers—broad-leaved shooting star, spring gold desert-parsley, early blue violet, chocolate lily, and camas. Tiny starbursts, bells, and chandeliers made of petals blanket these wide, open lands, fashioning such contrast with the dark and emerald forest typical of western Washington. Put off your visit to run errands or linger at home, and you’ll miss this peak display. Prairie is like that. Full of fleeting beauty.

Come in summer for the birds and butterflies. Come for the refuge in the shade cast by the generous canopy of a Garry oak. In fall, with the leaves gone, come for the “fantastic silhouette” of the trees—the gnarled limbs, narrowing to a wild canopy of thin curling branches. It is a land of many catch-it-while-you-can moments and only-here sightings. On a sunny clear day at the Schibig prairie, you can see the snowy behemoth that is Mount Rainier, rising 14,411 feet in elevation. It’s a staggering and memorable juxtaposition. It’s prairie, South Sound style.