Testing Amazon Transitional Forest Leaf Flammability: Combustion Experiment Flammability Metrics (2015)

Intensifying land use practices and global climate change are leading to increased forest fragmentation and more severe droughts in the southeastern transitional forests of the Brazilian Amazon. The combination of land use and droughts has increased fire frequency, intensity, and extent in the region. Various plant traits can either limit or promote flammability, as demonstrated in many seasonally dry environments (e.g. Mediterranean shrublands), which are home to species that are adapted to frequent fire. However, little research has been done to associate flammability with the leaf traits of humid tropical forest species that are experiencing fire with greater frequency and severity than historically recorded. In this study, the leaf traits and consequent burning characteristics of seventeen species abundant in a transitional forest plot in Mato Grosso, Brazil were analyzed through controlled combustion experiments and trait measurements. Principal components analysis and linear regression were employed to compare leaf traits and their ability to predict flammability. The results reported herein show that these species demonstrate variability in flammability. Individual leaf surface area and leaf volume were found to be the most significant predictors of flammability among these species. The most flammable species were those with thin, lightweight leaves that become arranged in loosely packed, highly aerated fuelbeds and would be able to drive rapidly moving, high intensity fire across the forest floor, consuming a larger amount of fuel. The less flammable species were characterized by thick, heavy leaves that create dense fuelbeds, potentially inhibiting fire spread and the overall consumption of available fuels. Analyzing the dynamics between leaf traits and plant flammability with forest composition, successional trajectories and future fire behavior could lead to an examination of overall landscape effects in which certain species with fire-adaptive strategies could outcompete more fire-sensitive species, therefore influencing future fire regimes. Furthermore, given a scenario of increasing fire, this knowledge can lead to more effective conservation and land use policies in tropical regions.