Soil properties and charcoal dynamics of burnt soils in the Tyrolean Limestone Alps

We investigated soil samples of four burnt slopes in the Tyrolean Limestone Alps of varying age after fire (wildfires occurred in 2003, 1962, 1946, and in 1250 AD) as well as of the surrounding soils that were not affected by combustion. Charcoal content of the O and A horizons was determined as well as pH, soil organic matter content and C/N ratio. The results showed a background value of charcoal in all soils with a dominance of charcoal in the O horizon of the youngest burnt slope (2003). With vegetation and soil recovery, charcoal concentrations decreased and zones of maximum charcoal accumulation shifted further down in the soil profile. Soil organic matter contents significantly decreased on burnt slopes, which is due to vegetation combustion, long-term vegetation changes and intensified erosion. However, in the long-term, re-accumulation occurs due to the recovery of vegetation. Soil pH increased by combustion and was further modified by an altered vegetation composition. C/N ratios remained largely stable, with the soil N content reacting more sensitive to combustion. The results demonstrate that Alpine regions react sensitively to wildfires due to the steep slope angle, which causes not only short-term but also long-term modification in vegetation composition and erosion.