Skip to Main Content View Text-Only

Environmental Services

working for clean rivers

Phone: 503-823-7740

Fax: 503-823-6995

1120 SW 5th Avenue, Room 1000, Portland, OR 97204

Table of Contents
Habitat and Biological Communities
The descriptions below provide general information for each topic. Click on each topic to get subwatershed specific descriptions.

Aquatic Habitat
This section focuses on aquatic features relative to fish and wildlife habitat. Please see the other sections of this characterization (particularly the Hydrology section) for additional information on the conditions or distribution of streams, wetlands, lakes, and the Willamette River.

Historic conditions in this context refers to the conditions before significant alteration from non-native settlement, most of which occurred after 1850. Since then, the Willamette Watershed Planning Area has undergone extensive urban development.

Prior to development, the Willamette River floodplain was intact and interconnected with the river’s main channel and side channels through the Planning Area. The floodplain provided storage for floodwaters and sediment, nutrient exchange, groundwater and wetland recharge, a source of organic material, and a refuge for fish and wildlife.


Fish Communities
This section focuses on the specific conditions of fish communities. Please see the other sections of this characterization (particularly the Aquatic Habitat parameter) for additional information related to the conditions and distribution of fish habitat.

Historic conditions in this context refers to the conditions before significant alteration from non-native settlement, most of which occurred after 1850. Since then, the Willamette Watershed Planning Area has undergone extensive urban development.

Altman et al. (1997) provide an extensive description of current fish communities throughout the Willamette Basin and identify introduced species through the basin. This is a comprehensive study of existing studies and an important background document for understanding regional scale patterns in Portland communities. Altman et al. (1997) report that ODFW (1988) identified 54 species as being present within the Willamette Basin, and identified 7 additional species from other sources (see Table 3, pp. 22-23 in Altman et al. 1997). Forty-eight percent of these were introduced species. Additional studies have provided information specific to the Lower Willamette River. Fish communities have been documented through the Willamette River Fish Study (ODFW 2001; 2002), and through a series of studies on the Lower Willamette River over the years. The Willamette River Inventory(City of Portland Bureau of Planning, 2000) provides a detailed reach-by-reach description of fish communities and their habitats in the Lower Willamette River through Portland.

The poor health of fish populations in the Lower Willamette River is reflected in part by the large numbers of exotic species present within the community, and in part by the listings of many of the regions populations under the Endangered Species Act (ESA) (see ESA Status Summary Table). In March 1998 and March 1999, NOAA Fisheries issued final rules to list four evolutionarily significant units (ESUs) of steelhead (Oncorhynchus mykiss) and chinook salmon (O. tshawytscha) as threatened under the federal ESA. Earlier, in May 1997, NOAA Fisheries designated the Lower Columbia River/ Southwest Washington ESU of coho salmon (O. kisutch) as a candidate for possible listing, and in 2000 the Oregon Department of Fish and Wildlife listed Lower Columbia River coho as endangered under the state’s Endangered Species Act. In addition, in March 1999 the U.S. Fish and Wildlife Service (USFWS) proposed the Southwest Washington/ Columbia River ESU of coastal cutthroat trout (O. clarki) for listing as threatened under the ESA. The USFWS decided not to list this cutthroat ESU in June 2002, but the service has announced its intent to begin a status review of the species, and that review may result in a listing.

Portland’s watersheds and waterways are within these six salmonid ESUs. Within Portland’s Willamette Watershed Planning Area, the salmonids use the Willamette River and several other smaller west side streams as detailed within each subwatershed or river segment discussion.


Macroinvertebrate Communities
This section focuses on the specific conditions of macroinvertebrate communities. Please see the other sections of this characterization (particularly the Aquatic Habitat parameter) for additional information related to the conditions and distribution of macorinvertebrate habitat.

Historic conditions in this context refers to the conditions before significant alteration from non-native settlement, most of which occurred after 1850. Since then, the Willamette Watershed Planning Area has undergone extensive urban development.

Altman et al. (1997) provide an extensive description of current macroinvertebrate communities throughout the Willamette Basin and identifying introduced species through the basin. This is a comprehensive study of existing studies and an important background document for understanding regional scale patterns in Portland biological communities.


Plant Communities
This section focuses on plant communities and their function as habitat. Please see the other sections of this characterization for additional information related to the conditions and distribution of vegetated areas.

Historic conditions in this context refers to the conditions before significant alteration from non-native settlement, most of which occurred after 1850. Since then, the Willamette Watershed Planning Area has undergone extensive urban development.

The climax vegetation of the West Hills is the Western hemlock/sword fern forest (Franklin and Blinn, 1987). Natural wildfires and extensive logging and burning in the early 20th century created favorable conditions for pioneer species to establish, including Douglas fir, red alder, and black cottonwood. Although considered more of a shade-tolerant species, bigleaf maple quickly establishes after fires because of its ability to resprout.

Current plant species described for each subwatershed do not constitue an exhaustive list. Most of the species listed are based on observations by city staff during field inventories. Vegetation cover was visually estimated using reconstructions of general land surveys (historic) and 2002 aerial photography (current). Estimates of current vegetation cover does not take into account impervious surfaces that may be underneath tree or shrub canopies.

Vegetation moderates the effects of temperature, wind, and precipitation; stabilizes the soil; and slows run-off from storm events. Tree and shrub roots are important components of soil integrity, especially in areas like the West Hills where landslides are relatively common. Cities are typically warmer, up to 20 degrees difference, than surrounding rural or undeveloped areas (Johnson and O'Neil, 2001). This is most likely to due to the sparse vegetation cover and a high amount of dark impervious surfaces that retain heat.

The composition and structure of vegetation strongly influences the abundance and diversity of wildlife species. In general, a complex habitat with multiple vegetation layers (i.e. herbaceous, shrub, and canopy layers) provides more niches than a simplified habitat, such as fallow field. Exotic plant species threaten to simplify and degrade native habitat. Modifications include a decrease in plant diversity and a reduction in insect prey. Evidence suggests that native plants support more insect species than exotic plants (Marzluff, 1997 and Johnson and O'Neil, 2001).


Riparian Habitat
This section focuses on riparian areas as they function as fish and wildlife habitat. Please see the other sections of this characterization for additional information related to the conditions and locations of riparian areas.

Historic conditions in this context refers to the conditions before significant alteration from non-native settlement, most of which occurred after 1850. Since then, the Willamette Watershed Planning Area has undergone extensive urban development. In general, Euro-American settlement of the area first occurred near the Willamette river, where riparian vegetation was cleared to create tillable land (Hulse et al., 2002).

Riparian areas provide a number of critical functions, the most important of which are temperature moderation, reduction of sedimentation and erosion, and nutrient source. Riparian zones cover a small portion of the landscape (1-2%), but provide critical foraging, breeding, and resting habitat for a large percentage of species (>50%, Johnson and O'Neil, 2001). Riparian areas with adequate vegetation diversity provide for a variety of food sources for aquatic species. Riparian widths will vary with topography, geology, and soils and with the degree of development. A minimum width of approximately 150 feet is necessary to ensure stream shading, inputs of wood, and invertebrate species necessary to aquatic species.

Current riparian areas are assessed by considering land within 300 feet of stream banks based on the area covering most riparian functions. In 2002, Metro completed an inventory of regionally significant riparian and wildlife habitat resources. The City of Portland Bureau of Planning is currently working on an update to the City’s natural resource inventory.


Wildlife Communities
This section focuses on wildlife communities. Please see the other sections of this characterization (particularly Aquatic Habitat, Riparian Habitat, and Plant Communities) for additional information related to the conditions and distribution of wildlife habitat. Each subwatershed provides a variety of ecosystem functions, most notably habitat connectivity. Riparian areas, large tracts of contiguous habitat, and to a certain extent, vegetated parkways, serve to connect proximate natural resource areas.

Historic conditions in this context refers to the conditions before significant alteration from non-native settlement, most of which occurred after 1850. Since then, the Willamette Watershed Planning Area has undergone extensive urban development

Because of the sparse distribution and low density of the historic human populations in the project area, ecological processes pre-1800s were largely intact and functioning with little anthropogenic disturbances. Exceptions to this may have been intensive trapping of fur-bearing animals by Europeans and use of fire by Native Americans. Unchecked hunting by Hudson Bay trapper’s almost eradicated beaver from the Willamette Valley by the 1830s (Hulse et al., 2002). Indigenous tribes used fire mostly in low-lying grasslands throughout the basin for the production of food and fiber (Hulse et al., 2002). Historic ecosystem function and wildlife-habitat interactions in this subwatershed may have been indirectly affected by smoke and displaced wildlife from fires burning in the lowlands.

Terrestrial species that were once prevalent in the Willamette Valley include the grizzly bear, California condor, yellow-billed cuckoo, Lewis’ woodpecker, the black-crowned night heron, and the gray wolf (Hulse et al., 2002). The Oregon spotted frog and the western pond turtle were historically more abundant in the lower Willamette River and may have inhabited the backwater areas along the shoreline of the Willamette River.

Exotic species or common native species adapted to human activity have become a more significant part of wildlife species composition as urbanization has occured. Dominant exotic avian species include the European starling, house sparrow, and rock dove. Ground-nesting birds or those associated with dense understory habitat tend to disappear as areas become urbanized. This is mainly due to a reduction in habitat and food base (Johnson and O'Neil, 2001). Atlman et al. (1997) provide an extensive description of current wildlife communities throughout the Willamette Basin, describing amphibian, reptile, bird, mammal communities and identifying introduced species through the basin. This is a comprehensive study of existing studies and an important background document for understanding regional scale patterns in Portland wildlife communities. Additional studies such as Portland’s significant natural resource inventories provide information specific to portions of the Willamette Watershed. These inventories were prepared by the Bureau of Planning and describe key habitat and wildlife communities at the resource site scale for resource sites located in tributary watersheds. In 2000 the Bureau of Planning also produced a draft inventory of biological communities and wildlife habitat resources in and along the Willamette River in Portland.

Maps & Files

Questions & Comments
If you have any questions or comments on our web site, please contact our webmaster.