Plant Traits Rather than Species Richness Explain Ecological Processes in Subtropical Forests

Functional traits and species richness have been used to assess variation in ecological functions in multiple ecosystems. However, biodiversity effects on ecosystem functioning could differ between ecosystem types and evaluating these associations could help assess ecosystem recovery in restoration sites. The objective of this study was to analyze the effect of species richness and plant functional traits on ecological processes related to nutrient cycling, productivity and regeneration in subtropical forest ecosystems. The study was performed in three sites (each site containing a reference forest and a forest undergoing restoration) located in the south of Brazil. We collected data on understory abundance, aboveground biomass, litter stock, decomposition, soil feeding activity, litter and soil quality and evaluated the association with tree species richness and plant traits (both community-weighted mean trait values-CWM, and functional diversity measures). Variables related to plant functional traits, especially CWM measures, were associated with most of the ecological processes analyzed. Leaf traits showed the strongest effect on the processes, especially for aboveground biomass, litter stock and understory abundance. Most relationships did not differ between reference and restoration sites. Our results support the mass-ratio theory, suggesting that dominant species traits are the ones that strongly affect ecosystem functioning, and suggest a secondary role of species number on the ecological processes analyzed. Our study provides evidence for the usefulness of functional traits to assess changes in ecological processes in forest ecosystems, with similar patterns in reference forests and forests undergoing restoration.