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

Abstract

Forest fires can produce significant impacts on the structure and functioning of natural ecosystems. In march 2015, a largescale
forest fire affected Araucaria araucana-Nothofagus pumilio (araucaria-lenga) forests of high ecological value in
National Reserve China Muerta (Chile, 38° S), where fire adaptations are rare among native plants. The goal of this research
was to evaluate the initial changes of plant composition in the forest along a severity gradient (i.e., high, medium and low
severity) one year after fire. It is hypothesized that areas more affected by fire will have different species composition from
the less-fire-affected areas, with decreased richness and abundance of native species, but exotic species will be favored by
the less severe fire. Twenty sampling plots of 100 m2 each were established throughout the fire-severity gradient, including an
adjacent 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 floristic
composition and similarity between the different levels of severity. The results show that species richness and abundance
were significantly lower in areas of high and medium fire-severity compared to areas less-affected by fire. The richness and
abundance of exotic species were greater in areas of low fire-severity, which were subject to cattle grazing after the fire. This
research shows a rapid compositional change in the vascular plant community in Araucaria-Nothofagus forests one year after
fire, and raises the potential for change in the forest structure if dominant tree species are unable to recover after fire.