This project documents the extent of riparian vegetation loss during a period of rapid development (1990-2008) in three Oregon cities. Aerial photographs, at a 1-foot resolution, of the study cities were digitized, analyzed, and completed for four points in time (1990, 1997, 2002 and 2008). Stream locations and city boundaries were obtained from the Metro RLIS database (Metro, 2002). All the data were projected to North American Datum of 1983. The banding analysis was conducted to measure vegetation coverage in four riparian vegetation classes for all permanent streams and wetland features at eight buffer widths from streams (7.5 m, 15 m, 22.5 m, 30 m, 45 m, 61 m, 100 m and 200 m).
Four vegetation classes analyzed were based on a two-by-two classification, adjacent vs. all, and woody vs. unmanaged. The ’adjacent’ classification includes all woody and unmanaged vegetation cover adjacent to stream within the buffer width, with adjacency determined by a 5 m separation distance (Schuft et al., 1999); while the ‘all’ classification includes all cover of a given vegetation class (either ‘woody’ or ‘unmanaged’) within a given buffer width, regardless of separation distance from other similar cover. These determinations produced the following four classifications:
a) Adjacent woody: included trees and shrubs, within 5 m distance of a stream and/or other adjacent woody cover.
b) Adjacent unmanaged: included adjacent woody, plus unmanaged herbaceous plants within 5 m distance of a stream and/or other unmanaged adjacent vegetation cover.
c) All woody: included adjacent woody plus non-adjacent trees and shrubs.
d) All unmanaged: included adjacent unmanaged, plus non-adjacent trees and shrubs.
Ted Hart, Vivek Shandas
Investigate the performance of local development policies that protect riparian vegetation in three cities in the Portland, OR metropolitan area.
Analyze the extent of vegetation loss along stream corridors between the years 1990 – 2008, to determine whether management strategies correlate with different on-the-ground losses of riparian vegetation and clarify the dynamics of riparian vegetation loss on the ground and with respect to management issues to better equip urban resource managers and policy makers in all urbanizing areas to craft effective policies for the future.
The project focuses on three main questions: 1) What has been the extent of vegetation loss along stream corridors during the recent wave of development?; 2) Have different local management approaches resulted in varied rates or patterns of loss?; and 3) What are the major, particularly anthropogenic, causes of vegetation loss?.