Relative contribution of niche and neutral processes on tree species turnover across scales in seasonal forests of NW Argentina

Environmental heterogeneity and dispersal limitation influence tree species distribution, but their relative contributions change with the spatial scale of analysis. We analyzed tree species turnover using twenty 1-ha permanent plots to quantify variation in floristic similarity explained by environmental factors and geographical distance at regional (among plots) and local (within plots) scales in seasonal premontane forests of northwestern Argentina. We related floristic similarity (Bray–Curtis) with environmental variation and geographical distance using specific regression models (regression of distance matrix and mixed-effects models at regional and local scales, respectively). Floristic similarity decreased with distance at both spatial scales but its relative contribution was significant only at the regional scale (18 and <1 % at regional and local scale, respectively). Dispersal limitation may be a relevant process at biogeographical scale where dispersion at large distances become infrequent for some species. In addition, we identified that regional climatic and topographic gradients and local edaphic variation contribute to explain floristic similarity across scales in seasonal premontane forests. Environmental heterogeneity explained about the same variance in floristic similarity at regional and local scales (7 and 8 %, respectively). We conclude that quantitative aspects of floristic patterns, such as the relative contribution of niche and neutral processes to explain species distribution, can strengthen conservation strategies at different spatial scales, and therefore could be a useful tool in conservation planning.