Habitat and Biological Communities
Historically, the Willamette River in the Portland area comprised an extensive and interconnected system of active channels, open slack waters, emergent wetlands, riparian forest, and adjacent upland forests. There was high habitat connection, both longitudinally along the river and laterally from the vegetated riverbanks to the upland forests. Vegetation types included bottomland forests in the low riparian areas and the forested wetlands (black cottonwood, Oregon ash, willow). Denser mixed conifer forests (Douglas fir, big leaf maple, western red cedar, western hemlock, grand fir, red alder) dominated the West Hills and were found in some parts of the east terrace. Both foothillsavanna (Oregon white oak, Pacific madrone, Ponderosa pine, Douglas fir, red alder, big leaf maple) and meadow (grasses) were found in the east side.
Upland habitats have been heavily impacted by development in the upland portions of the watershed with the exception of Forest Park. In addition, significant dredging, diking, and channeling of the mainstem Willamette has occurred in the Portland area. The mainstem has been narrowed and deepened, and off-channel habitat has been virtually eliminated. The river's banks have been hardened precluding important naturally caused channel changes and minimizing the interaction between the river and riparian and floodplain vegetation. Habitat has been simplified and large tracts of riparian vegetation have been cleared. Actions taken as a result of new regulations and improving scientific knowledge are beginning to reverse some of these trends. However, continued demand for riverside industrial and residential land, and for development in upland areas, has the potential to compete with efforts to improve habitat.
Constriction of the riverbank by fill, docks, and seawalls has caused the river channel to become deeper and smoother. This has reduced the channel complexity, which is now rated as poor for both native and non-native fish habitat. Channel complexity in the form of variation in depth, channel meanders, side channels, banks, logs, rocks, gravel bars, etc. provided habitat for fish as well as for plant, insect, and other species on which fish depend. Channel complexity also provided both velocity and predator refuge and gravels in the this reach of the river may have been used as Chinook spawning areas. Maintenance dredging to support commercial shipping and transportation activities also likely contributes to the lack of channel complexity.
Urbanization has substantially altered much of the historic upland habitat. The remaining habitat is fragmented and isolated. In the east side, less than 800 acres of natural vegetative area remain. In the west side, over 8,200 acres remain, primarily in undeveloped areas in the West Hills, Forest Park, and the Balch Creek Watershed. Invasive, non-native species (including English ivy, reed canarygrass, Himalayan blackberry) dominate in many areas. They threaten existing natural areas by reducing forest structure, diversity, and habitat value, and are very difficult to control.
A few small high-quality natural areas provide valuable habitat and watershed health benefits remain within the Willamette plan area. The Swan Island lagoon and other terminal facilities in the Industrial section provide areas for fish and wildlife to move out of the river's main current (off-channel habitat). The north segment of the Willamette between the St Johns Bridge and the confluence with the Columbia River includes both remnant off-channel areas and relatively intact bank conditions. Even after years of aggregate mining, Ross Island provides valuable off-channel and shallow water habitat, relatively intact streamside vegetation, and natural bank conditions. The adjacent wetlands at Oaks Bottom also provide valuable watershed functions.
All of Portland's riverside parks provide important watershed benefits. Powers Marine, Sellwood, Willamette, Oaks Bottom, Cathedral, and Kelley Point Parks represent, to varying degrees, the remaining natural riparian areas within the City. Although Stevens Creek has been affected by urbanization, its confluence with the Willamette just north of the Sellwood Bridge provides important fish habitat.
Even though the lower reaches are blocked by culverts, the upper reaches of Balch, Saltzman, Doane, and several unnamed creeks in Forest Park have been protected from intensive development because they are located mostly within the park. While recreational use does cause some erosion, the water quality, hydrology, and habitat in the streams' upper reaches contribute to watershed health. Several of these streams also support populations of cutthroat trout, sculpin and other native fish (see Biological Communities, below). Even if fish passage is not restored, the confluence areas of these streams provide valuable watershed health benefits.
Development has greatly reduced biotic integrity of the plan area and the mainstem Willamette. Some native species of fish and aquatic insects have been extirpated, and introduced species currently occupy their habitat or compete with them for food, cover and other habitat features.
The fish and wildlife species that use the lower Willamette River have changed significantly from historical conditions. Some sensitive species have become extinct. The introduction of nonnative species, particularly warm water fish, has increased competition for food and habitat for native species. At least 39 native and introduced species of both warm-water and cool-water fish inhabit the lower Willamette River today. The most dominant species (in order of population) are northern squawfish, black crappie, white crappie, largemouth bass, smallmouth bass, and walleye.
Thousands of anadromous salmonids (including steelhead, Chinook, and coho salmon) swim through Portland on their way to spawning and rearing areas upstream, and their offspring must return as they travel out to the Pacific Ocean. Chinook and steelhead are listed as threatened under the federal Endangered Species Act, and coho are listed as endangered under Oregon's Endangered Species Act.