Contrasting distribution patterns of invasive and naturalized non‐native species along environmental gradients in a semi‐arid montane ecosystem. Issue 4 (22nd June 2015) - Andersen, Kelly M.
Abstract Questions Mountain systems have high abiotic heterogeneity over local spatial scales, offering natural experiments for examining plant species invasions. We ask whether functional groupings explain non‐native species spread into native vegetation and up elevation gradients. We examine whether non‐native species distribution patterns are related to environmental variables after controlling for elevation and, thus, driven by niche processes. Location The Wallowa Mountains, northeast Oregon, USA. Methods We surveyed non‐native plant species along three mountain roads and into the native habitat matrix to assess the extent of invasion success along distance from roadside and elevation gradients. We used GLM to predict single species occurrence probabilities, LMM to examine differences in distribution patterns among functional types, and pCCA to examine multivariate responses of the non‐native community to ecological variables. Results Probability of occurrence of the eight focal invasive species was not significantly related to distance from the road, but declined with elevation. Non‐native species with annual life history strategies were more restricted to lower elevations than perennial species. Non‐native species considered invasive occurred at lower minimum elevations than naturalized species. Shifts in the species composition of the non‐native plant community were related to changes in soil and climate variables. Conclusions Our results suggest that invasive species have similar patterns of habitat associations and spread from roadsides to interior vegetation zones, whereas naturalized species partition environmental gradients in this semi‐arid montane ecosystem. Furthermore, annual and invasive species groups occupy lower elevations and perennial and naturalized species groups have invaded further up the mountain roads and into the native vegetation. Thus, functional groupings may explain contrasting distribution patterns of non‐native species and could be used to inform management strategies for non‐native species.