Biodiversity Guide - The Intertwine

egional conservation strategybiodiversity guideAppendix I WatershedsRiver IslandsWhen Lewis and Clark traveled down the Columbiathey initially missed the Willamette Riverbecause the confluence area was hidden behindnumerous islands. With the extensive shallowwater, ephemeral shoaling, dynamic delta,and Missoula Flood deposits, there were manyephemeral islands in addition to large, permanentislands. Today we know those islands as GovernmentIsland, Hayden Island, Sauvie Island, SwanIsland, Ross Island, and Elk Rock Island. Theislands provided safe nesting and rearing sites forbirds, migratory stopover habitat, flood attenuation,sources of gravel for mainstem spawningfish, wood for complexity, and other benefits tothe river.Elk Rock Island currently represents the mostintact example of the riverine islands. Its habitatis a mix of oak and madrone forest with somefirs, with emergent wetland vegetation near thefringes. Swan Island is completely altered, filled toconnect with the mainland and provide additionaldevelopment property. In the early 1900s SwanIsland was the location for Portland Airport,before the area was developed for industrial use.Undeveloped areas of Sauvie and Hayden islandslikely represent the type of habitat lost on SwanIsland: prairie grasslands and riparian forest withmixed ash and cottonwood and some oak trees.The bluffs (discussed below) still contain some ofthis remnant habitat.Upland Habitats and ConnectivityThe Missoula Floods are primarily responsiblefor the topography of the area that remainstoday. On the east are buttes, terraces, and ridges,surrounded by flatter lands consistent with analluvial floodplain. Before 1850 these areas were amix of wetland, prairie, oak, and mixed coniferdeciduousand riparian forest. These areas weredrained by numerous permanent and ephemeraltributaries. As the habitat transitioned towardthe river, it became a riparian forest with cedar,cottonwood, willow, ash, and native shrubs. Thereare two distinctive bluffs on the east side of theriver—one near Swan Island and one near OaksBottom—that continue to provide oak habitats.These bluffs also provide unique habitat for hawksand falcons. Currently, Portland’s total canopycoverage is 27 percent.The west side of the river is dominated bythe Tualatin Hills formation known as the WestHills, which stretches from Tryon Creek to SauvieIsland and includes Forest Park. In upland areas,oak occupied shallowsoils and drier microclimatesand mixedconifer-deciduousforest was the dominantlandcover types.The river floodplainwas a complex mix ofwetland, riparian, andfloodplain types.Large-scale vegetationremoval occurredthroughout this areabut most predominantlyon the east sidebecause of urbanizationand development.Remnant habitatpatches remain, butthey tend to be altered and often isolated. Thewestside uplands and hills remain the most intactbut are impaired by large areas of invasive speciessuch as ivy and blackberry.The transition from the uplands to the riverhas been heavily altered. Many of the creeks thatdrain the west side have been piped underground,combined with sewer sent to the treatment plant,or eliminated altogether. The low-lying areashave been heavily developed. Riverview/PowersMarine, Harborton forest and wetlands, andKelley Point Park provide the few remaining areaswhere there is some connectivity. As a result, thetributary processes such as wood and sedimenttransport, off-channel habitat, riverine habitat,nutrient delivery, and cooling benefits have beensignificantly constrained. Lowland habitat thatdiffered in vegetation from the upland foresthas been significantly altered and replaced withimpervious surfaces.Fish and Wildlife SpeciesLewis and Clark famously noted the abundantwildlife in the area: “I [s]lept but verry little lastnight for the noise Kept [up] during the wholeof the night by the Swans, Geese, white and GreyBrant Ducks &c…they were emensely numerous,and their noise horrid” (The Journals of Lewisand Clark, p.277). It is difficult to know howmany species of fish were present historically.Today, 61 fish species are present in the lowerWillamette, approximately half of them native.There are 16 salmon and steelhead species orevolutionarily significant units (ESUs) that areprotected under the federal Endangered SpeciesAct. Lamprey—a culturally and ecologicallysignificant native fish—are declining but stillfound in the lower Willamette and are harvestedby tribal members at Willamette Falls. White andgreen sturgeon species are believed to be decliningin this area but research is ongoing.Bottomland forests and wetlands providehabitat for waterfowl, shorebirds and Neotropicalmigratory birds, including songbirds, kingfishers,cormorants, great blue herons, and ducks. Mammalspecies such as river otter, mink, weasel, deer,coyote, fox, and beaver still use the area. Reptilesand amphibians, including red-legged frogs, westernpainted turtles, and salamanders, are found inthe sloughs and wetlands.The bluffs and higher forests provide habitatfor raptors such as hawks, eagles, osprey, andperegrine falcons; Neotropical migrants, includingwarblers, flycatchers, swallows, and tanagers;resident or short-distance migrant birds such asrobins, chickadees, wrens, thrushes, sparrows,towhee, and kinglets; and bats. Remnant oakhabitats are also used by several oak specialistspecies, including slender-billed (white-breasted)nuthatch, western gray squirrel (in some largerconnected patches), and several moth and invertebratespecies.Although this represents robust biodiversity inan urban area, it is a small fraction of the historicalpopulations. Many of the remaining speciesare tracked as ESA candidate species or state speciesof concern.Conservation PrioritiesConservation priorities and efforts for this watershedare detailed in numerous local, state, andfederal documents. Generally, the documents prioritizeprotecting and restoring key habitats andreintroducing lost habitat types and species. Thisis being partly addressed through acquisition,restoration, invasive species removal programs.and land use planning. Water quality protectionis also a key priority. Efforts include the largestinfrastructure project in the history of Portlandto reduce the number of sewer overflows directlyinto the Willamette and advancements in innovativestormwater treatment such as green streets,rain gardens, and ecoroofs. Finally, contaminatedsediment remediation continues to be an ongoingfocus, especially with the cleanup of the PortlandHarbor Superfund site and the ongoing remediationof the Columbia Slough sediments. Some ofthe key programs that are occurring and ongoingin the area include Portland Harbor, the Cityof Portland’s Watershed Management Plan andRiver Plan, Metro’s Bond Measure AcquisitionProgram, and a multi-jurisdictional sustainable288289