Burn severity in Araucaria araucana forests of northern Patagonia: tree mortality scales up to burn severity at plot scale, mediated by topography and climatic context

Abstract

Climate change is forcing shifts in wildfire regimes, altering post-fire processes, and threatening the persistence of species and ecosystems. Key to assessing the potential for post-fire conversion to an alternate vegetation type is understanding drivers of burn severity, which in turn influence the material legacies that determine post-fire recovery. In Andean Patagonia, pyrophytic (fire promoting) shrublands juxtaposed with pyrophobic (fire inhibiting) forests of fire-sensitive species are well documented as drivers of fire spread and burn severity. However, the capacity of the highly fire- resistant Araucaria araucana to either promote or dampen burn severity has not previously been examined. This study uses field and remotely sensed data to examine which variables control burn severity at tree-, plot- and fire event-scales in large fires that burned A. araucana-dominated vegetation in four large fire events from 1987 to 2014. Logistic models were developed for each of the three scales to test for the factors influencing burn severity. Our results show that at the level of the individual tree, crown connectivity, tree size, and species strongly affect probability of death of individual trees. At a plot level, stand stocking parameters are less strongly predictive of burn severity. At a landscape-scale, vegetation type and topography, along with climatic and weather conditions are strong drivers of burn severity. These findings quantify the importance of greater tree size in the survival of the fire-resistant A. araucana and reinforce the regional pattern of greater fire severity being associated with tall shrubland vegetation in comparison to forests.