USDA Forest Service Proceedings RMRS-P-42CD
Riparian plants, Urbanization -- Oregon -- Portland, Sustainability
Riparian vegetation buffer loss was investigated for three cities with contrasting local regulatory controls in urbanizing northwest Oregon. The cities examined were Hillsboro, Oregon City and Portland, all having experienced high rates of population increase in the 1990s. All cities are covered under Oregon’s land use law that provides goals for the protection of open space and natural resources. On the municipality level, regulatory controls in Portland included a system of environmental zoning for riparian area protection, while regulatory controls on development in riparian areas in Hillsboro and Oregon City were less stringent. Digital aerial photographs covering buffer areas within 200 m of all permanent streams for these cities were digitized for the years 1990 and 1997 using criteria including minimum inter-patch distance of 5 m for adjacent classes and minimum patch area of 20 m2. Cover classes were divided into vegetation areas adjacent to stream and total, as well as woody and unmanaged vegetation areas. Banding analysis was performed for these vegetation coverages for several buffer widths out to 100 m from streams. Results for the 1990 to 1997 period showed larger losses for unmanaged adjacent vegetation 100 m from stream for Hillsboro and Oregon City (≥1.5 percent/year) than for Portland (/year). For adjacent tree vegetation within a 100 m buffer width, again Hillsboro and Oregon City had higher rates of loss (>1 percent/year), while Portland lost trees in the 100 m buffer at a lower rate (/ year). Factors explaining these lower rates of riparian buffer loss for Portland may include both a higher amount of riparian area in public ownership and more stringent local regulatory controls on development in riparian buffers. These results also demonstrate that vegetated riparian buffers continue to be lost due to development in growing Oregon municipalities regardless of the level of regulatory protection.
Yeakley, J. A.; Ozawa, C. P.; Hook, A. M. 2006. Changes in riparian vegetation buffers in response to development in three Oregon cities. In: Aguirre-Bravo, C.; Pellicane, Patrick J.; Burns, Denver P.; and Draggan, Sidney, Eds. 2006. Monitoring Science and Technology Symposium: Unifying Knowledge for Sustainability in the Western Hemisphere Proceedings RMRS-P-42CD. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. p. 296-302