Differences in floristic composition of Araucaria-Nothofagus forests affected by mixed levels of fire severity

Forest fires can produce significant impacts on the structure and functioning of natural ecosystems. In march 2015, a largescaleforest fire affected Araucaria araucana-Nothofagus pumilio (araucaria-lenga) forests of high ecological value inNational Reserve China Muerta (Chile, 38° S), where fire adaptations are rare among native plants. The goal of this researchwas to evaluate the initial changes of plant composition in the forest along a severity gradient (i.e., high, medium and lowseverity) one year after fire. It is hypothesized that areas more affected by fire will have different species composition fromthe less-fire-affected areas, with decreased richness and abundance of native species, but exotic species will be favored bythe less severe fire. Twenty sampling plots of 100 m2 each were established throughout the fire-severity gradient, including anadjacent unburned forest that served as reference. Species richness and abundance of all vascular plants (native and exotic)were recorded in each plot. We analyzed and compared species richness and abundance of natives and exotics, and the floristiccomposition and similarity between the different levels of severity. The results show that species richness and abundancewere significantly lower in areas of high and medium fire-severity compared to areas less-affected by fire. The richness andabundance of exotic species were greater in areas of low fire-severity, which were subject to cattle grazing after the fire. Thisresearch shows a rapid compositional change in the vascular plant community in Araucaria-Nothofagus forests one year afterfire, and raises the potential for change in the forest structure if dominant tree species are unable to recover after fire.