Clark’s Prairie

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Garry oaks mark the former extent of Clark’s Prairie. Photo by Karen O’Brien.

In 1852 E. A. Clark and John Harvey, fresh from the California gold rush, staked adjacent claims and built a cabin just south of here in an area that came to be called Clark’s Prairie. They probably picked this spot because the natural oak prairie or savanna here required less forest to be cleared in order to farm. Evidence of Clark’s Prairie can still be seen in the Garry oaks found in Seward Park and Martha Washington Park, in the local street names Oakhurst and Oaklawn, and in the fire-adapted plants associated with oak ecosystems that are found on the south side of Pinoy Hill. Seward Park is home to Seattle’s only significant grove of Garry oaks (Quercus garryana), also known as Oregon white oaks. More than twenty of these elegant, slow-growing, and drought-tolerant trees are located at the south end of the park, most prominently just east of the turnaround in the south parking lot. Additional oaks have been planted more recently on Pinoy Hill and near picnic shelters #4 and #5.

Fire Ecology

Oak prairies and savannas are the most threatened ecosystems in western Washington, because cities have been built over them and because of a century of fire suppression. Native Americans maintained these ecosystems against the encroachment of Douglas-fir forests by burning them. Thick-barked Garry oak and other fire-adapted prairie plants survive fires that kill Douglas–firs and hemlocks. Native Americans encouraged prairies because they were rich in game and edible plants, including acorns. An 1861 land survey from this area mentions oaks and describes “deadenings” that suggest active burning by the local Lake People, who may have planted the oaks here.

Snowbrush is a fire-adapted species that requires fire to germinate its seeds. Snowbrush can fix nitrogen like lichens, legumes or alder, giving it an advantage in re-colonizing burned-over areas after a fire. Snowbrush or sticky laurel is easily recognized by its sprays of white flowers and its evergreen sticky leaves with three prominent veins. Extremely rare in Seattle, a few snowbrush have been found scattered on the south hillside, but are in decline.

Other shrubs and trees associated with Garry oak in Seward Park include madrona, snowberry, Nootka rose, and poison-oak.


Poison-oak is not an oak but a member of the sumac family. Its three leaflets turn crimson in the fall.

Poison-oak is uncommon in Seattle but abundant on the south side of Pinoy Hill. It is a fire-adapted species that is unrelated to oaks, but shares their habitat. While most people are highly allergic to poison-oak resin containing the compound urushiol, the California Indians used poison-oak in basketry without ill effects. The shiny leaves of three leaflets turn brilliant crimson in the fall.

The following rhyme may serve as a mnemonic to help recognize poison-oak:

“Leaflets three, let it be
Berries white, poisonous sight”

Persons exposed to poison-oak should wash their exposed skin as well as clothing and pets that may have urushiol on their fur. Rubbing alcohol may be more
effective in removing urushiol than soap and water, although once urushiol has penetrated the skin there is little chance of washing it off. Creams containing oxidizing enzymes can destroy urushiol, but will have little effect
once it has penetrated the epidermis. The accepted treatment for poison-oak rash is hydrocortisone. Severe cases should be treated by a doctor.

Oak apple galls

These apple-like galls are induced on oaks by gall wasps that use them to protect their larvae.

The only animal specifically associated with oak ecosystems resident at Clark’s Prairie is the oak apple gall wasp Andricus quercuscalifornicus, which breeds
in the oaks. Oak apple galls are so-named because they resemble apples in size and shape, and are initially red before turning beige, giving the peculiar impression of
apples fruiting on the branches of oak trees. These galls form after a gall wasp lays about a dozen eggs on an oak stem in the fall. The galls develop the following spring,
and are presumed to be induced by hormones secreted by the gall wasp eggs or larvae, re-directing the oak cells to build a protective gall around the insects. The larvae occupy separate central chambers, and emerge the following fall.

Although galls can be formed on many plants by fungi, mites, and other organisms, about half of all species of galls are formed by gall wasps (Cynipidae), and similarly
about half of all species of galls are found on oaks. Gall wasps and oaks have co-evolved for millennia, and many gall wasps have complex life cycles with alternating
generations of springtime sexual reproduction by males and females and summer-fall parthenogenetic reproduction by females only, with the two generations
often forming distinct kinds of galls on different parts of the same tree. In oak apple galls, only parthenogenetic females have been reported, and no alternate generation
of males and females has been observed. Galls may become inhabited by a whole community of inquilines and parasites taking advantage of the protection of the
gall. Parasitic halcid, braconid, and ichneumonid wasps all are known make their homes in oak apple galls. The galls can persist through multiple years and provide
habitat for other insects. Sapsuckers may try to pierce through the gall to get the inhabitants.

Restoring the oak community

In 2007 the Friends of Seward Park received a grant from the Washington Native Plant Society to help restore the understory of Clark’s Prairie in Seward Park, both for habitat enhancement and for public education about Washington’s oak ecosystems. The Friends partnered with Seattle Parks and Recreation, Seward Park Environmental and Audubon Center, sixth grade classes from Orca K-8 School and other volunteers to plant over 200 prairie plants including camas, chocolate lily, Henderson’s shooting star, and Roemer’s fescue. Camas, distinguished by its blue flowers in spring, was a major prairie food plant for native peoples throughout the west. Camas bulbs were boiled, roasted in pits, or dried and ground into flour for making cakes.

Garry Oak prairie on the south shore of the peninsula