Summary1. Exotic invasive plants can alter ecosystem structure and function, yet there is a paucity of evidence regarding broadly applicable mechanisms. We hypothesized that denser growth patterns characteristic of exotic invasive plants lead to a common effect of reduction and homogenization of environmental temperatures and that these alterations compromise thermal quality of habitat for ectotherms. 2. We quantified thermal regimes within native and exotic plant-dominated habitats, including monocultures of 11 exotic species as well as stratified mixed-exotic habitats in a temperate forest landscape in the eastern US. 3. Exotic plant-dominated habitats exhibited reduced and less variable temperature compared to their native counterparts, with stratified mixed-exotic habitats exhibiting the lowest temperatures overall and exotic shrubs (six species) the lowest as a structural group. Thermal effects were extended beyond the growing season of native vegetation owing to extended leaf phenology of exotic woody species. 4. To demonstrate that these effects can alter environmental cues and adversely impact native species, we used a 4-year radiotelemetry study and laboratory thermal preference trials to relate habitat thermal quality to multiscale resource selection by a native snake, Agkistrodon contortrix. To further test the effect of vegetation structure and the efficacy of targeted management, we removed exotic foliar cover from eight 400 m 2 plots.5. Radio-tagged snakes avoided exotic vegetation at multiple spatial scales. In contrast to previous studies of A. contortrix, snakes exhibited preference for sites composed of higher native vegetation density and height. Response to exotic foliage removal was also rapid -including use of sites during gestation and parturition. 6. Together with other recent studies, our results suggest a direct, non-trophic effect that is common to a broad range of exotic invasive plant species in a variety of ecological contexts. We further offer a mitigation technique that may be implemented when large-scale control or eradication is not cost-effective or ecologically sound.

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