Cumulative effects of salvage logging and slash removal on erosion, soil functioning indicators and vegetation in a severely burned area in NW Spain

Post-fire salvage logging, a common practice in productive forest stands, can lead to increased soil erosion and loss of soil quality. However, further field research is required to confirm and clarify these effects. This study was conducted in NW Spain, in productive mixed stands of P. sylvestris and P. pinaster affected in the summer of 2015 by a crown fire that caused a high level of soil burn severity. Salvage logging was carried out nine months after the fire, and the effects of logging slash retention and slash removal were compared after a further two years. The study objectives were: i) to assess soil loss in the pre-logging period and compare it with the soil losses accumulated during the two post-logging annual periods, ii) to determine whether logging slash can mitigate soil erosion after post-fire logging and iii) to compare the effects of slash cover and slash removal on soil physical, chemical and microbiological parameters and vegetation recovery and iv) to evaluate the short-term effect of salvage logging on soil functionality. Soil loss in the period between the wildfire and salvage logging (September-June) was 4.2 Mg ha−1. Soil loss was significantly lower (by 2.4 times) in the post-salvage logging period than in the pre-logging period. Slash cover significantly reduced soil loss (2.6 compared with 1.7 Mg ha−1), with no detrimental effect on soil properties and no effect on the recovery of natural vegetation cover. Around three years after a wildfire followed by logging, while soil physical parameters analyzed did not show values reflecting a severe impact, symptoms of delayed recovery of soil microbial and enzymatic attributes were detected. Our study also revealed a contrasting difference between the slow recovery of the soil physical and microbial properties and the rapid recovery of the vegetation. Further research will be needed to clarify that response.