Fine-scale topography shape richness, community composition, stem and biomass hyperdominant species in Brazilian Atlantic forest

Abstract

Topography is an important driver that determines diversity patterns and ecosystem functioning in tropical forests. However, there are few studies analyzing contrasting topographical conditions on the relative importance of species to ecosystem functioning, mainly on those who have a greater contribution (i.e., hyperdominant species). We aimed to evaluate whether contrasting topographical conditions determine changes in tree species richness, community composition, and the number of stem and biomass hyperdominant species in a Brazilian Atlantic remnant forest fragment. We selected two areas on distinct hillsides with contrasting topographic conditions, at the biological reserve of the Federal University of Viçosa, Minas Gerais state, southeastern Brazil. Each area (100 × 100 m) was sub-divided into 100 plots of 10 × 10 m. From each plot, all trees having diameter at breast height (DBH) ≥ 10 cm were identified to the species level and tagged for measurement. We measured three topographic variables (slope, elevation, and convexity) in each plot, based on the assumption that these variables may affect tree species diversity, species composition, and ecosystem function (aboveground biomass). The AGB of individual stems was calculated in all plots. We performed a multivariate regression tree for estimating topographical heterogeneity in each area. We found that species richness differed significantly between areas. Species richness in the Northeast area (the more topographically heterogeneous one) was 48% higher than that in the Southeast area, which is less topographically heterogeneous. The tree species composition varied considerably between areas, with similar AGB patterns being registered among plots. The number of stem hyperdominants varied significantly between areas. In the Southeast area, only two species out of the 85 recorded (2.38%) accounted for 50% of the number of stems hyperdominants, while in the Northeast area 10 species (7.94%) accounted for 50% of stems hyperdominants. Our results showed that high topographic heterogeneity induces high species richness and that the number of stem and biomass hyperdominant species increase along with richness on a local scale. Based on our results, we presume that biomass hyperdominance can also strongly influence forest ecosystem functioning on a local scale.