3d. Urban Forest
Portland’s existing tree canopy covers about 26% of Portland’s land area. The current goal is to have trees cover at least 33% of the city. The tree canopy is most dense in natural areas, such as Forest Park, other parts of the West Hills, on and around Powell Butte and other eastside buttes, and parts of Pleasant Valley in the southeast. Areas with the most concentrated urban development, particularly the Central City, and also industrial areas have the sparsest canopy.
This map shows the distribution of trees in the city, including dispersed canopy, clusters of trees and swaths of canopy extending through some residential areas. Canopy has expanded in some areas over the last 30 years, including in many Inner Neighborhoods due in large part to the planting of new street trees and the growth of established trees. Other areas, such as in some outer southeast and southwestern neighborhoods, have seen losses of mature trees to make room for new development.
Portland’s urban forest consists of trees along city streets and around houses, businesses and institutions, and trees and vegetation in parks and natural areas. Currently, trees cover about 26 percent of Portland’s land area—roughly half on private property and half on public property. North Portland and the city’s higher density residential, commercial and industrial areas have the sparsest tree canopy.
Although overall tree canopy cover in Portland has increased slightly over the last 30 years the City is not meeting its goals for tree canopy cover:
Much more is known about trees on public property than on privately owned land in the city. Portland’s parks and parking strips have at least 170 different types of trees. More than half of them are deciduous (primarily maple), and about half are smaller than 6 inches in diameter. Large trees (30 inches in diameter and larger) represent less than 10 percent of Portland’s park and street trees. Not surprisingly, large-growing native species such as Douglas fir and western hemlock are more common in Portland’s parks and natural areas than along its city streets.
Because trees play an important role in maintaining watershed functions, the Bureau of Environmental Services (BES) has planted more than 2 million trees citywide as part of its Watershed Revegetation Program. Tree planting in Portland continues through the efforts of the City, Friends of Trees and other organizations.
Currently, trees in City natural areas such as Forest Park, and neighboring properties are at risk of damage from catastrophic wildfire, as a result of long-term fire suppression and the consequent buildup of fuels. Fire suppression also has allowed the conifer population to out-compete native oak and madrone trees, resulting in declines in these native trees, habitat loss and increased fire susceptibility in some areas.
It appears that in parts of Portland, large trees and groves are being removed as a result of development and being replaced with smaller species that fit on small lots and narrow parking strips. Of particular community concern is the removal of remnant stands of native Oregon white oak and madrone trees on the Willamette bluffs, and Douglas fir trees in outer southeast Portland to accommodate infill residential development. Current landscaping regulations that apply to new development are achieving only a fraction of the target canopy levels established for residential, commercial and industrial development. Additionally, for some areas of the city where there are many aging, large trees of the same species, disease can spread quickly because the trees are homogenous and in close proximity to each other. Removal of these trees has a substantial impact on neighborhood character.