1120 SW 5th Avenue, Room 1000, Portland, OR 97204
Historic The bottomland along the Willamette River likely contained a rich mix of wetland, prairie, scrub-shrub, and riparian forest habitats. Riparian vegetation would have been dominated by ash, cottonwood, and willow and most likely contained ninebark, red-osier dogwood, and other native scrub-shrub species.
According to reconstructions of land survey records from 1851 to 1865, the vegetation circa 1850 above the terrace consisted of upland mixed conifer forest. This forest type consisted of varying combinations of Douglas fir, western hemlock, red cedar, grand fir, scattered with big-leaf maple, red alder, dogwood, and white oak. The understory of this forest type likely included vine maple, huckleberry, thimbleberry, rhododendron, yew, salal, hazel, ferns, devil’s club, and Oregon grape. Large stands of western red cedar, with no fir and very little hemlock, were once prevalent in the West Hills (City of Portland Bureau of Planning, 1991a). The red cedar climax forest type occurs on wet, lower slopes within the western hemlock zone.
The upper portion of this subwatershed burned sometime in the mid 1800’s according to the early land surveys (Hulse, et al., 2002). Fires occurred relatively frequently throughout the Willamette valley from at least 1647 to 1848 (Hulse, et al., 2002). Burning of brush piles was associated with logging, which occurred from the arrival of the settlers in 1840 until about 1950 (City of Portland Bureau of Planning, 1991b). The most recent substantial fire in Forest Park burned about 1,200 acres in 1951, shortly after the park was dedicated. In general, natural and man-made fires on the west side would have occurred primarily on the drier ridge tops and slopes, but specific fire frequency is unknown.
Current Vegetation, including trees and shrubs, appears to cover 95% of the subwatershed based on visual estimation of 2002 aerial photography. Approximately 5% of the subwatershed consists of residential/cleared areas.
Vegetation cover types in this subwatershed include old growth (2%), mid-age conifer (15%), mature hardwood (4%), conifer topping hardwood (45%), hardwood with young conifer (22%), shrub (3%), grass/forb (4%), and cultivated areas/developed (5%).
The canopy of the watershed is currently dominated by Douglas fir and bigleaf maple. Other common and widely distributed trees in Forest Park include western hemlock, western red cedar, red alder, grand fir, black cottonwood, and Pacific yew. Hemlock, red cedar, and grand fir are slow growing, shade-tolerant species that currently occupy the sub canopy in Forest Park. Over time and in the absence of major disturbances, these species will outgrow Douglas fir and dominate the canopy. A healthy stand of Pacific dogwood and a rare specimen of western white pine occur in this subwatershed (City of Portland Bureau of Planning, 1991b). Old growth Douglas fir trees (400 – 600 years old) and large specimens of western hemlock, western red cedar, and pacific yew occur in the lower Miller Creek Canyon (City of Portland Bureau of Planning, 1991b).
Current understory plants include sword fern, dwarf Oregon grape, vanilla-leaf, vine maple, and salal (City of Portland Bureau of Planning, 1995). Western wahoo is found along wet streambanks throughout Forest Park. This subwatershed contains the only known specimens of the giant rattlesnake plantain (Goodyera oblongifolia) and spotted coral root (Corallorhiza maculata)—both in the orchid family.
Crane’s bill (Geranium sp.) has spread into the lower basin and threatens to dominate the mesic herbaceous community. Non-native plants have established in the cleared areas under the power lines that traverse the subwatershed. English holly and Himalayan blackberry have invaded portions of the forest (City of Portland Bureau of Planning, 1991b).
Assessment Processes that have led to alterations to vegetation communities inlude logging, introduction of non-native invasive species, and clearing land for roads, residences, and infrastructure (electrical towers).