||Dynamac Corp., Corvallis, OR. ;Oregon State Univ., Corvallis. Dept. of Fisheries and Wildlife. ;National Forage Seed Production Research Center, Corvallis, OR.;National Health and Environmental Effects Research Lab., Corvallis, OR.
Much of the native riparian vegetation of the Willamette Valley, Oregon, has been replaced with agricultural crops or invasive non-native plant species. Detailed information about current Willamette Valley riparian vegetation is generally lacking. Plant specie composition data are useful in a variety of applications, including condition assessment, environmental monitoring and restoration planning. The objective of this study was to characterize the vegetation of three contrasting riparian sites occurring in the Willamette Valley. W determined plant species composition and abundance at a non-cultivated herbaceous site and a cultivated site, both located along Lake Creek, an intermittent stream, and at a forested site located along the Calapooia River, a perennial stream. All sites were adjacent to intensively-managed perennial ryegrass seed production fields. Crop agriculture strongly encroached on the Lake Creek sites, whereas the Calapooia site had received little encroachment from agricultural coversion. At Lake Creek, we inventoried 32 species at the non-cultivated herbaceous site and 18 species at the cultivated site, most of which were non-native. The cultivated site was dominated by wetland-adapted species in the area closest to the creek where perennial ryegrass was absent. Approximately half of the species at the non-cultivated herbaceous site were facultative upland species, and the site was dominated by introduced pasture grasses. In contrast, the 53 species inventoried at the forested site were mostly native and wetland-adapted. The forested site was dominated by Poplus balsamifera ssp, trichocarap T. & G., Pseudotsuga menziessii (Mirbel) Franco, and Acer macrophyllum Pursh, with extensive shrub and herbaceous strata. Results show a range of vegetative conditions found in riparian areas of the Willamette Valley and reflect the influence of differing hydrologic regimes and agricultural impacts.