Decadal effect of post-fire management treatments on soil carbon and nutrient concentrations in a burnt Mediterranean forest

Abstract

Wildfires and post-fire burnt-wood management treatments disturb the soils of forest ecosystems. However, little attention has been paid to the impact of these compound disturbances from a medium- to long-term perspective. In this study, we compared the decadal effect on soil carbon and nutrient concentrations (i.e. C, N, K and P) of two post-fire burnt wood treatments that differed in management intensity. We established two blocks differing in elevation, each including three replicates (ca. 3 ha) of each of two treatments: salvage logging (SL), a treatment that emulated a conventional salvage logging (although logs of dead wood were stacked within-plots in piles covering < 5% of the area), and a treatment where 90% of the burnt trees were manually cut but all biomass was haphazardly spread over the ground (partial cut, PC). Soil carbon and nutrient concentrations were compared across treatments, across the bare soil of both treatments, and in areas of bare soil versus areas below burnt trunks within the PC treatment. All analyzed soil chemical properties differed between elevation blocks. Moreover, C, K and P concentrations were higher in the PC treatment than in the SL treatment, although effect sizes were small. Similarly, C and P were higher in the bare soil of the PC treatment than in the bare soil of the SL treatment. However, the soil away from logs and the soil underneath logs did not show significant differences for C, N, K and P concentrations within the PC treatment, suggesting that scattered dead wood originated a higher log cover that physically protects the soil and enhances nutrient availability. Our findings indicate that, a decade after wildfire and treatment implementation, salvage logging produced lower soil carbon and nutrient concentrations than another management treatment which left all wood scattered over the ground. Studying the long-lasting impacts of post-fire management strategies is essential to propose suitable management approaches that contribute to recover soil nutrient availability.