LAUSR

We investigated the interrelations between environmental variables (proxies for water availability and soil physico-chemical properties) and tree community patterns (diversity, composition and structure) along pond-upland topographic gradients within depressional watersheds in the upper Uruguay River basin in southern Brazil. Sampling plots were allocated in four topographic habitats: (1) inside ponds (wetland sites) and (2) immediately outside them, and in areas with (3) 60 cm and (4) 120 cm of elevation in relation to their limits (upland sites). Environmental conditions and forest composition varied along pond-upland gradients, but the diversity and structure of tree communities did not. Species turnover was associated with changes in topography-driven environmental conditions, notably water availability. Depressional watersheds show regionally unique abiotic and biotic features but are virtually unprotected by Brazilian private land legislation.