Resource availability shapes fire-filtered savannas

Abstract

[Questions]

Humid savannas can be considered fire-filtered landscapes because fire is very frequent (<10 yr return intervals) and only fire-resistant species can occur. This flammable vegetation can be functionally heterogeneous, structurally and floristically patchy. We hypothesized that resource availability (mainly water and nutrient availabilities) accounted for most of the functional and phylogenetic spatial structure of communities across these savanna landscapes. [Location]

Emas National Park, central Brazil. [Methods]

We used individual-based functional trait, phylogenetic and environmental data combined with spatial information to assess the main drivers and mechanisms of community functional change (turnover) in a large fire-filtered savanna landscape. We used Mantel correlograms and a maximum rank correlation approach to assess the spatial structure and the subset of landscape factors that best predict compositional, phylogenetic, species-based and individual-based functional community turnovers and the mechanism by which they do operate. [Results]

Communities were spatially structured across the landscape, presenting functional convergence at shorter distances and divergence at larger distances. All of the turnover metrics presented unique spatial structures and were correlated with a unique set of landscape predictors. Soil texture accounted for the largest fraction of the spatial structure, but soil N availability, pH, altitude and fire frequency were also important. [Conclusions]

Our results support the idea that the patchy distribution of water and nutrients mediated by clay content shape community membership in fire-filtered savannas, whereas current variations in fire frequency interact with resource availability to shift community attributes from species average trait values (intraspecific variability).