Ecologia do fogo e diversidade funcional em comunidades vegetais de cerrado no Parque Nacional das Emas

Abstract

Fire is an environmental filter that selects species based on their traits and, in association with soil features are related to differences in plant species richness and composition. Functional diversity incorporates variation in species traits and allows one to evaluate the effects of biodiversity upon community functioning. It can be divided into components to elucidate response and effect links with environment. Both intra- and interspecific variation should be considered when analysing the role of environmental filters structuring communities. Sampling woody plants in a Brazilian cerrado reserve, we measured species richness, functional traits, abundance, environmental variables and litter decomposition rate. We calculate three functional diversity index. Then, we used model selection analyses to select the best model predicting functional diversity and richness based on soil variables in sites with three different fire frequencies. We calculated the community weighted mean of each trait and used an ordination to examine how traits changed across fire frequencies. We tested for effects of biodiversity upon ecological functioning. We also used an intra- and interspecific trait-based approach to test for shifts in each trait mean, reduction of trait range, and increase in niche differentiation. We found higher species richness and functional dispersion in more fertile sites where fire was frequent, and the opposite where fire was infrequent. However, soil influenced functional evenness and divergence only where fire was infrequent, with higher values where soils were poorer. We found low values of functional richness and high values of functional evenness and functional convergence. Functional components were related to environmental variables, indicating that functional diversity had response links with the environment: harsher environmental conditions lead to less phenotypic overlap and, consequently, less competition. Functional components did not predict litter decomposition rate. However, when environmental variables were also used, we found higher decomposition rate related to higher slope, richer soil, frequent fire, and higher functional richness. Therefore the effect links of functional diversity upon functioning were dependent on the cerrado environment. The inclusion of intraspecific variability did not increase the perception of environmental filters and competition to all traits. We found evidence for environmental filter to almost all traits analysed, except basal area and leaf toughness. Mean values shifted for five traits and ranges reduced for seven traits compared to null expectation. Also five traits presented niche differentiation indicating competition after the filter selection. Fire may change functional traits directly by hindering development of plants and indirectly by changing competition. Different fire frequencies lead to different plant-soil relationships, which may affect the functioning of tropical savanna communities. Both functional diversity components and functional identity of the communities are affected by fire frequency and soil conditions. Fire gradient changed the space traits by selecting similar species with more adequate traits.