A importância de características de flamabilidade para compreensão de resistência e resiliência de comunidades vegetais ao fogo e à seca

Abstract

Climate change has extensively altered the environment and among its predicted effects are increases in drought and fire events. Thereby, the way species deal with these factors can determine the patterns of dominance of species in a plant community. Understanding response mechanisms of the species to fire can be aided through on the inclusion of functional characteristics (morphological, physiological and phenological measured at the individual level). This work aimed to understand what the characteristics of fire resistance are, as well as assessing the relationship between the patterns of dominance of the species and their characteristics of drought resistance. The first hypothesis is that the species most resistant to fire will exhibit higher drought resistance indicating a convergence of the species to deal with different factors from an overlap of strategies. The second hypothesis is that the dominant species will be the most flammable, but have greater investment in resilience strategies. The study was carried out in the Highland Grasslands of Itatiaia National Park, located in the state of Rio de Janeiro, Brazil. The functional characteristics of flammability of 12 species were measured through ignition and combustion tests. Linear regressions and principal component analysis were performed to understand the relationship between flammability characteristics and characteristics of resilience, drought resistance and relative frequency of species. Contrasting to the expectations/hypotheses, the species more resistant to drought presented a high flammability due to high maximum combustion rates and a large proportion of burned biomass, and these species were the most frequent in the Highland Grasslands. Nevertheless, this increased flammability was not associated with greater resilience. This study demonstrates that flammability should be considered as a multidimensional theoretical variable and that the use of functional characteristics of flammability provides more concrete evidence about fire as a key factor in structuring plant communities. The higher frequency of the most flammable species can be explained by a rapidly-flammable strategy, which promotes greater protection of their gems and meristematic tissues. On the other hand, difference found in the patterns of resilience of the species could be explained by other factors, such as the proportion of carbon reserve present in plant tissues. In addition, the study demonstrated that analyzing the response of species to both fire and drought can provide a more robust explanation of the patterns of dominance, since there is a high probability of these factors co-occurring. In the light of climate change, studies that seek to jointly understand the different dimensions of flammability through an integration with response to drought are crucial, since the responses of plants to these factors are associated