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CHARACTERIZATION OF RIPARIAN VEGETATION IN OFF-CHANNEL HABITATS AND RELATIONSHIPS WITH ANNUAL FLOODING PATTERNS, UPPER MAIN STEM, WILLAMETTE RIVER, OREGON
Citation:
Cline, S P., L. McAllister, W. W. Carson, AND P. K. Haggerty. CHARACTERIZATION OF RIPARIAN VEGETATION IN OFF-CHANNEL HABITATS AND RELATIONSHIPS WITH ANNUAL FLOODING PATTERNS, UPPER MAIN STEM, WILLAMETTE RIVER, OREGON. Presented at Intgernational Conference on Riparian Ecology and Management in Multi-Land Use Watersheds, Portland, OR, August 27-31, 2000.
Description:
Hydrogeomorphic processes drive riparian vegetation establishment, growth, and longevity. The stage of vegetation development (e.g. age, composition, height, density) affects its degree of functionality with respect to hydrology, nutrient cycling, and terrestrial and aquatic habitat support in off-channel habitats. We hypothesized that distinct riparian vegetation assemblages were associated with fluvial surfaces formed by hydrogeomorphic processes. To evaluate this hypothesis we developed low-flow, digital, base maps of vegetation, terrain, and aquatic off-channel habitat from 1998, 1:24000 and 1:6000 aerial photos using mono- and stereoscopic photogrammetric plotters. Similarly, digital, water inundation maps were developed from oblique, 35-mm photos acquired in 1998-99 over 17 alcoves at discharges (stages) between 145 and 1486 m3s-1 (0.6 and 3.7 m, respectively), as recorded at the USGS gaging station at Harrisburg. Mapped vegetation polygons were ground sampled at summer low flows in 1998-99 for vascular plant composition and cover, tree ages and heights, and elevations from global positioning. Inundation lines from oblique photos were orientated to the 1998 base map via space resection, forming the basis of a GIS analysis of the relationship between stage, elevation of fluvial surface, and vegetation type. We will present maps of the distribution of vegetation types associated with off-channel habitats, and conceptual models of vegetation development in relation to fluvial surfaces controlled by geomorphic processes. These maps and models serve as a basis to examine historical changes leading to current conditions, estimate the current level of functionality of riparian vegetation on key processes, and evaluate hypotheses regarding estimates of future vegetation change after restoration of hydrogeomorphic potential of the Willamette River.