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RELATIONSHIPS OF ALIEN PLANT SPECIES ABUNDANCE TO RIPARIAN VEGETATION, ENVIRONMENT, AND DISTURBANCE
Magee, T. K., P L. Ringold, AND M. Bollman. RELATIONSHIPS OF ALIEN PLANT SPECIES ABUNDANCE TO RIPARIAN VEGETATION, ENVIRONMENT, AND DISTURBANCE. Presented at 47th Annual Symposium of the International Association of Vegetation Science, Kailua-Kona, Hawaii, July 18-23, 2004.
Riparian ecosystems are often invaded by alien species. We evaluated vegetation, environment, and disturbance conditions and their interrelationships with alien species abundance along reaches of 29 streams in eastern Oregon, USA. Using flexible-BETA clustering, indicator species analysis, and non-metric multidimensional scaling (NMS), we characterized four vegetation series (Lodgepole pine/shrub/meadow, Engelmann spruce-Grand-fir-Douglas-fir, Ponderosa pine/Snowberry, Sagebrush/Juniper/Cheatgrass-Bluebunch wheatgrass) and their assemblages. Correlation of environmental (n = 31) and disturbance (n = 31) variables with NMS axis scores showed vegetation distributed along complex gradients associated with elevation, precipitation, landform, watershed area, disturbance, grazing, and buffer condition. Comparing NMS for native species only and for all species demonstrated homogenization of species composition with addition of alien species. Differences in alien cover were observed between vegetation types (Kruskal-Wallis, p 0.000). Spearman correlations (p 0.006) identified negative relationships between alien cover and elevation, precipitation, tree basal area, distance to road, buffer condition, and native species diversity, while positive relationships occurred with watershed area, disturbance, agriculture, and grazing. Differences in species composition and native diversity illustrate negative effects associated with alien cover. The vegetation types vary in intensity of invasion. Environmental and disturbance metrics may serve as predictors of potential invasion intensity.