Local-scale elevation patterns of Atlantic Forest tree community variation and assembly drivers in a conservation hotspot in southeastern Brazil

Abstract

Understanding natural community assembly along elevational gradients has long attracted the attention of ecologists and botanists. Here, we study a tropical local-scale elevational gradient at a dissected mountainous terrain to understand if drivers of tree community variation and assembly patterns are similar to those reported for greater spatial distances and elevational gradients in the Atlantic Forest region. We inventoried trees with Diameter at Breast Height (DBH) ≥5.0 cm in 154 plots (10 × 10 m; 1.54 ha) systematically distributed along a local-scale (<1 km2) steep environmental gradient ranging between 100 and 640 m of elevation (a.s.l.) in southeastern Brazil; we also recorded environmental conditions (litter, soil characteristics and topographic variables) and the geographic coordinates of each plot. We detected 297 species and 61 families. Several species of the tree community displayed relevance (importance values) variation patterns along the elevational gradient. Species richness and diversity levels peaked near the middle of the local-scale elevational gradient. Although there was a strong indication of spatial structure effects, environmental effects were more relevant to explain the patterns of tree community assembly. The evidence supports the presence of a continuous gradual change of dominant tree species and indicates, for the first time, that community variation patterns commonly detected over greater spatial distances and elevational gradients can occur within a local-scale (small spatial distance) elevational gradient of a rough mountainous terrain. Findings help to consolidate that niche-related environmental effects associated to the heterogeneous environment (litter, soil and topography) of a tropical mountainous conservation hotspot can have greater influence than neutral-related spatial effects over tree community assembly from local to regional-scales.