Soil Vulnerability Indicators to Degradation by Wildfires in Torres del Paine National Park (Patagonia, Chile)

Wildfires are a common phenomenon globally, nonetheless some ecosystems are more adapted than others. In this work, we show results of a study conducted in Torres del Paine National Park (Chile) that suffered a big forest fire in 2011, affecting 17,666 ha. The Park is located in the transitional forest-steppe zone whose annual rainfall varies between 300 and 1,500 mm. Plant communities goes from Patagonian steppe, pre-Andean scrub to Magellanic forest. Based on vegetation community and trying to cover all representative sectors affected by the fire, 5 areas of the park were sampled in 2019 following the transects where a vegetation recovery study has been monitored since the fire occurred. Soil parameters used to evaluate were: texture, soil water repellency (WR), organic matter (OM), and aggregation, including total content of macroaggregates (TCA) and their stability (AS). The results showed high values of OM, however three of the 5 areas showed statistically lower values of OM in burned samples. WR was present (from slight to severe) in the 75% of the samples, and without differences between burned and unburned. The correlations analyses indicated that WR is more related with the OM type than with quantity, since better correlations were obtained when only samples from the same area were included in the analyses. The results of aggregation indicated that soils have a poor structural development. The TCA varies from 16 to 50%, and the AS is not very high (average of 66%), being the highest in the area with lowest TCA and more affected by the fire and erosion processes. This suggests that the higher values of AS are a consequence of the destruction and loss of the less resistant fraction after the fire. The combination of the high sand content (low specific surface area) and high OM make them very susceptible to develop WR. Since these soils have a scarce development with a poor structure, the combination of the WR and the poor soil structure make them very vulnerable to erosion processes after the fire. Measures to protect the soils or accelerate the recovery are recommended in these areas when new human caused wildfires could occur.