No 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 m 2 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.

Questions Fire is a key factor influencing Araucaria araucana forests, but the impact of fire severity on the understorey vegetation is not well understood. In this study we seek to answer the following questions: (a) how do initial plant diversity, composition and spatial distribution of the understorey vegetation change in response to different levels of fire severity; and (b) does the abundance of dominant tree species exhibit different patterns across a fire severity gradient shortly after fire? Location Old‐growth Araucaria araucana–Nothofagus pumilio forests in the Andes of south‐central Chile (38° S, 71° W) burned in 2015. Methods We evaluated the post‐fire plant regeneration across a fire severity gradient ranging from unburned forests to areas of high fire severity. One year after fire (in February 2016), we measured woody and herbaceous species richness, abundance, height, origin (native vs exotic species), life forms and the spatial pattern of plant recovery. Results Plant species richness and abundance were significantly higher within the unburned forest and low fire severity areas one year after fire, compared to areas of high and moderate fire severity. Overall, nearly 50% of the species present in the unburned forest were not found in areas of high severity, including the tree Nothofagus pumilio. Rapid vegetative resprouting of pioneer species such as Chusquea culeou resulted in an aggregated spatial distribution of plants after fire. Conclusions Plant diversity and the abundance of Araucaria araucana and Nothofagus pumilio were reduced in areas of high fire severity one year after fire. Exotic species were more abundant within areas of low severity, being likely mediated by cattle browsing. Our research makes clear the potential changes in forest composition and structure if dominant tree species are not capable of recovering after fire. We recommend the exclusion of cattle within fire‐affected areas and planting Nothofagus pumilio in areas of high fire severity.