Journal of Vegetation Science && (2015) Little evidence of native and non-native species influencing one another’s abundance and distribution in the herb layer of an oak woodland Mark A. Davis, Michael D. Anderson, Lilly Bock-Brownstein, Anna Staudenmaier, Melena Suliteanu, Amanda Wareham & Jerald J. Dosch Keywords Alliaria petiolata; Community assembly; Community composition; Competition; Deciduous forests; Eastern North American forests; Environmental heterogeneity; Herb layer; PAR; Topographic effects Nomenclature University of Minnesota Herbarium Received 19 August 2014 Accepted 31 March 2015 Co-ordinating Editor: Sandor Bartha Davis, M.A. (corresponding author, davis@macalester.edu), Anderson, M.D. (andersonm@macalester.edu), Bock-Brownstein, L. (lbockbro@macalester.edu), Staudenmaier, A. (astauden@macalester.edu), Suliteanu, M. (msulitea@macalester.edu), Wareham, A. (awareham@macalester.edu), Dosch, J.J. (dosch@macalester.edu) Department of Biology, Macalester College, Saint Paul, MN 55105, USA Abstract Question: To what extent are species, including native and non-native species, influencing one another’s distribution and abundance in the herb layer of a Minnesota oak woodland? Location: Oak woodland succeeding into a more mesic forest, on bluffland of the Mississippi River, east-central Minnesota. Methods: We collected plant composition and species cover data in 182 1.0 9 0.5 m quadrats regularly spaced on a 6-ha study grid in the oak wood- land. We also recorded slope, slope position, aspect, elevation and photosynthet- ically active radiation (PAR) at each quadrat. Results: Presence and abundance of other plant species, topographic variables and light availability explained only a small portion of the variation (5–19%) in the distribution and abundance of individual species. The most common strong- est predictor of cover for the ten most common species was species richness, with the association being positive. The non-native species, garlic mustard (Alliaria petiolata) exhibited the strongest positive association with species richness. Only one of the 45 pair-wise comparisons of the ten species resulted in a negative relationship between the species. Abundance and distribution of two species were associated with topographic features, but this accounted for much less of the variation in abundance than did species richness. Conclusion: We found little evidence that competition or any other interactions among common herb layer species, including the non-native Alliaria petiolata, play an important role in determining the abundance and the distribution of herb layer species in this oak woodland. Topographic factors may explain a small amount of the distribution and abundance patterns of a few species. But, for the most part, species are more likely to be present when other species are present, suggesting that they are simply establishing in microsites favourable to plants in general. Introduction Plant species abundance and composition can vary among sites due to differences in climate, macro-habitat differ- ences (including disturbance regimes), regional species pools and history among the sites (Peet et al. 2014b). Within sites, environmental heterogeneity, including both biotic and abiotic factors, can cause spatial variation in spe- cies abundance and composition (Stein et al. 2014). The abiotic factors can include micro-disturbances (Beatty 2014), heterogeneity in topography (Cantlon 1953), light availability (Pearcy et al. 1987) and a variety of edaphic factors, such as pH, moisture and soil nutrients (Peet et al. 2014a) some of which, e.g. light, water and nutrient avail- ability can, in turn, be influenced by biotic interactions such as competition (Tilman 1982). In the 1980s, interspecific competition, grounded in niche theory, was believed to be a primary driver of com- munity structure in general (MacArthur 1972) and in plant communities in particular (Tilman 1982, 1985; 1 Journal of Vegetation Science Doi: 10.1111/jvs.12302 © 2015 International Association for Vegetation Science