Fauna of Forest Park

Due to Forest Park's significant size and its continuous, unfragmented habitat, it boasts an impressive diversity of wildlife for an urban park. Currently, a tenuous corridor of natural vegetation connects the park's northwestern end to less developed areas and, ultimately, Oregon's Coast Range.

Mammals of Forest Park

As many as 62 mammal species use the forest habitat of Forest Park. Some of the more common species include the northern flying squirrel, Townsend's chipmunk, blacktail deer, mountain beaver, bobcat, coyote and long-tailed weasel. Tracks and droppings of black bear and cougar were also observed in past years.

Many of the species found in Forest Park are also found in the natural areas of Oregon's Coast Range. In addition to its habitat functions, the forested hills extending northwest from Portland toward the coast serve as a travel corridor for wildlife. This helps to facilitate the seasonal and long-term dispersal of individuals, helping to maintain genetic and biological diversity.

Birds of Forest Park

More than 100 species of birds reside in and/or use the forest habitat of Forest Park. Common residents include: Winter Wren, Dark-eyed junco, Spotted Towhee, Black-capped Chickadee, Chestnut-backed Chickadee, Golden-crowned Kinglet, Pileated Woodpecker, and Steller's Jay.

A number of long range migrants can also be spotted in Forest Park. Common examples include: Rufous Hummingbird, Olive-sided Flycatcher, Pacific-slope Flycatcher, Swainson's Thrush, and the Western Tanager.

Lesser known but extremely fascinating is the pygmy owl which makes its home in Forest Park and was the subject of an OPB Field Guide program.

Studies of relationships between composition of bird communities and habitat structure show that habitat fragmentation is a key factor in determining avian diversity. Studies indicate that as the degree of habitat fragmentation increases, avian species diversity decreases. Hence the importance of preserving nature’s corridor that connect Forest Park to wildlands extending to the Oregon Coast.

Fish in Forest Park

Only two streams in Forest Park are known to contain fish: Balch Creek and Miller Creek. The Balch basin is twice the size of the Miller basin and a substantial portion of Balch Creek flows year-round whereas only the lowest reaches of Miller Creek are perennial.

Balch Creek supports a substantial year-round but isolated population of cutthroat trout). The construction of a storm sewer in 1921 isolated the population from the Willamette River. As a result, the population may present unique genetic values.

The main stem of Miller Creek supports sea-run cutthroat trout which move freely to and from the Multnomah Channel. Coho salmon, cutthroat trout and steelhead have also been identified in the lower basin of Miller Creek. Miller is one of a small and diminishing number of free-flowing streams which provide spawning habitat for these anadromous fish.

Amphibians and Reptiles in Forest Park

The most recent data (1987) indicates that eight amphibians and two reptiles can be found in Forest Park. Common species include: Northern red-legged frogs, Pacific giant salamander, Dunn's salamander, and Pacific treefrogs.

Flora of Forest Park

Forest Park is located within what is known as the Western Hemlock zone. In its natural, undisturbed condition, this zone is populated by three primary tree species: Douglas-fir, western hemlock and western red cedar. To a lesser degree, grand fir, black cottonwood, red alder, bigleaf maple, madrone and western yew trees also occur throughout the landscape.

Shrubs are well developed, including: sword fern, salal, Oregon grape, lady fern, red huckleberry, vine maple, and western hazel are common and indicative species. Predominant wildflowers in this zone include wild ginger, inside-out flower, Hooker's fairy bells, vanilla leaf, evergreen violet, and trillium.

Forest Park has maintained all of the western hemlock zone's naturally evolved, characteristic plants. However, one change is significant today. Instead of being dominated by evergreen trees, the park is characterized by a preponderance of red alder and bigleaf maple trees. Primarily due to extensive logging, evergreen trees have declined appreciably while hardwood species have proliferated.

Relative Abundance of Habitat in Forest Park

Mixed deciduous/conifer

55%

Coniferous

29%

Urban/farmland

6%

Deciduous

5%

Meadow

3%

Old Growth

1%

Geology of Forest Park

Forest Park is situated on the east flank of the Tualatin Mountains. The park extends upslope from the Willamette River's flood plain to the crest of the Tualatin Mountains, an average distance of 1.5 miles. Elevations vary, from 75 feet along the Willamette River to 1,100 feet at the crest of Tualatin ridge.

The east flank of the Tualatin Mountains was formed by the dipping lava flows of the Columbia River Basalt Group. Forest Park's landscape is deeply dissected by streams originating along the crest and draining eastward to the Willamette River. Stream gradients recach as much as 11.5 percent, or 600 feet per mile. Inter-stream areas range from sharp ridges to narrow elongate plateaus. Benches in the eastward sloping mountain flank are also common.

Landslides have been a major factor in the recent geologic history of Forest Park. A fine layer of Portland Hills silt overlies Columbia River basalt, creating a very unstable formation - especially when wet. Considering the somewhat soggy winter climate of western Oregon, this makes for a poor foundation material. Ironically, the propensity for landslides has also been a significant factor in the preservation of Forest Park. Throughout Portland's history, a number of development schemes have been thwarted by unstable slopes.