HISTORIC LAND-COVER ANALYSIS OF THE LUCKIAMUTE RIVER BASIN, CENTRAL OREGON COAST RANGE: PRELIMINARY RESULTS FROM THE EARTH SCIENCE PROGRAM FOR UNDERGRADUATE RESEARCH AT WESTERN OREGON UNIVERSITY

Mountainous watersheds are fundamental landscape elements that form an important setting for local ecological interactions, human occupation, and water resource development. Since 2001, the Luckiamute River basin (Ad = 815 sq. km) in the central Oregon Coast Range has been used as a natural laboratory for undergraduate studies in surficial processes at Western Oregon University. This phase of the project presents preliminary results of land-cover analysis using aerial photography gathered over a time span of 64 years (1936, 1948, 1955, 1963, 1970, 1990, 2000).

Total length of the Luckiamute main stem is ~95 km. Two sites were selected for analysis: (1) the “upper reach” (50-62 km upstream from mouth); and (2) the “lower reach” (2-30 km upstream). Upper reach vegetation is comprised of 60% agricultural land and 40% conifer-hardwood forest, and that of the lower is 85% and 15%, respectively. A set of historic aerial photos were orthorectified and georegistered using GIS techniques. River channels were digitized and 500-m buffers created to form bounding riparian polygons. Land cover polygons were delineated and classified as either “forest canopy” or “cultivated open land”. Percent areal coverages and riparian canopy-buffer widths were measured for each time period. Significant differences were identified in land-cover patterns between the two study sites. Results are summarized as follows: (1) upper reach: avg. forest canopy area = 28%, avg. canopy-buffer width = 98 m, 16% increase in forest cover between 1970 and 2000, 3-fold increase in canopy-buffer width between 1970 and 2000; (2) lower reach: avg. forest canopy area = 33%, avg. canopy-buffer width = 310 m, 10% decrease in forest cover between 1948 and 1990; steady 52% decline in average canopy-buffer width between 1936 and 2000. These data suggest that the lower portion of the Luckiamute riparian zone is experiencing significant deforestation as part of agricultural practices. While the percent forest canopy in the upper reach was comparatively lower during most of the observation period, upland reforestation activities have significantly increased riparian tree cover in the past 30 years. Results of this study have important implications for watershed restoration planning. Additional land-cover analyses at four other sites are currently in progress.