Species or environment: what drives ecosystems processes in tropical forests?

Abstract

The ecosystem processes provided by tropical forests are of central importance to life on Earth. Brazil is a country with extensive vegetation coverage and great environmental heterogeneity, thus harbouring great biodiversity within its phytogeographical domains. To better understand the ecosystem processes along the time, the Long Lasting Ecological Projects are a very important tool, where an area is periodically revisited with biological information updated. Linking these data with climate, soil and biodiversity characteristics provides a set of important information about ecosystem functionality, which helps to understand and predict vegetation changes along the time. The present work sought to understand the role of climate, soil and biodiversity (taxonomic and phylogenetic) in the explanation of four ecosystem processes: aboveground biomass (AGB) storage, aboveground wood productivity (AGWP), mortality and recruitment of tree communities, along a seasonal gradient in the southeast of Brazil. Two work scales were considered: one at the fragment level (Site) and another at the plot level, being that in a Site there are several Plots. There was a tendency for higher values of AGB and AGWP in Evergreen Moist Forest, higher recruitment in Deciduous Tropical Forest and higher mortality in the Semideciduous Tropical Forest. The different scales showed different importance among the factors studied. On the larger scale, in addition to the environmental variables, floristic composition variables were also explanatory for AGB and mortality, while on the smaller scale, both taxonomic and phylogenetic biodiversity variables were important. We considered that the use of smaller scales, especially in more heterogeneous environments, can capture greater fineness of interactions, being able to provide more detailed explanation for the studied processes. Generally, in our study, environmental variables were more explicative of ecosystem process than biodiversity and we believe that it occurs because we worked in a seasonality gradient, where the difference in environmental characteristics among the forest types already define the presence of the species found in each of them. Even so, especially on a smaller scale, biodiversity variables can account for some of the variation in ecosystem processes.