Does structural connectivity influence tree species distributions and abundance in a naturally discontinuous tropical forest formation?

Aims The study of naturally discontinuous forest systems could help further our understanding of the relative roles of abiotic factors and spatial connectivity in influencing species turnover and plant metacommunity structure, compared to continuous forest formations, where local communities are often arbitrarily defined and where 'mass effects' and source-sink dynamics tend to confound the roles of dispersal and environment. Here we studied a tropical montane landscape where old-growth evergreen forest occurs as patchy formations in a matrix of natural grasslands, to test the influence of environment and connectivity on species turnover and woody plant metacommunity structure. Location Western and southern regions of the Upper Nilgiri Plateau, Western Ghats, southern India. Methods We sampled 85 vegetation plots located across a 600-km2 landscape, assembled environmental data, constructed contrasting spatial connectivity models, including models for the effects of topography on structural connectivity, and used RDA-based variation partitioning to assess the relative influence of environment and space on woody plant metacommunity structure. Results Considering several environmental and multi-scale spatial predictors, we could explain half of the variation in plant community structure. Environmental and habitat factors such as precipitation, temperature seasonality, elevation, fragment size and landscape context play a dominant role, explaining approximately 40% of variation. Spatial predictors based on Euclidean distance performed better than those that accounted for topographic resistance. Spatial predictors accounted for only 9% of the variation in plant metacommunity structure. Conclusion Our results support the species sorting paradigm of metacommunity structure, as abiotic effects and biotic interactions play dominant roles in influencing community structure and species turnover in these old-growth forests, with a comparatively small influence of spatial connectivity. Effective management of woody species diversity would therefore require conservation of these forests across the range of environmental conditions under which they occur. [ABSTRACT FROM AUTHOR]