Pre-fire forest management effectivity to decrease wildfire impact on soil properties in a Mediterranean forest.

Forest mechanical fuel treatments in Mediterranean ecosystems are frequently employed to reduce both the risk and severity of wildfires. These pre-fire treatments may influence the effects of wildfire events on soil properties. The aim of this study is to examine the effectivity of this treatment (clear-cutting operation whereby part of the vegetation was cut and left covering soil surface) carried out before a wildfire that broke out in 2015 and evaluate if the management had influence on post-wildfire soil properties of three sites: two exposed to management practices in 2005 (site M05B) and in 2015 (site M15B)–and one that did not undergo any management (NMB) and to compare their properties with those recorded in a Control area unaffected by 2015 wildfire. The fourth areas were sampled and compared 2, 10 and 18 months after wildfire. The study area is located in Ódena (Catalonia, Spain). The wildfire occurred at July 27^th of 2015 and burned 1237 ha. In each area and in each sampling moment we collected 9 topsoil samples (0-5 cm depth). We analyzed aggregate stability (AS), soil organic matter (SOM) content, total nitrogen (TN), carbon/nitrogen ratio (C/N), inorganic carbon (IC), pH, electrical conductivity (EC), extractable calcium (Ca), magnesium (Mg), sodium (Na), and potassium (K), microbial biomass carbon (C_mic) and basal soil respiration (BSR). Two-way ANOVA was carried out to check the differences according to sampling moment and to management. The results show that 2 months after the wildfire M05B showed greater amount of IC and pH; M15B showed greater Na than the other areas; NMB resulted higher in AS, TN, SOM, EC, Ca, Mg, K and BSR; and Control registered the highest C_mic. C/N resulted similar in the 4 areas in the three sampling moments. Ten months after wildfire, M05B showed greater AS and IC; NMB resulted higher in TN, SOM, EC, Mg and K; and Control showed higher pH, Ca, Na, C_mic and BSR. In the last sampling, 18 months after wildfire, M05B showed greater pH; M15B showed higher AS; NMB resulted higher in TN, SOM, EC, Ca and K; and Control showed higher IC, Mg, Na, C_mic and BSR. According to the treatments M05B registered higher TN, SOM, IC, EC, Mg, Na and K during 1^st sampling; AS and C/N during 2^nd sampling; and pH, Ca, C_mic and BSR during 3^rd sampling. M15B registered higher IC, Mg, Na and K during 1^st sampling; BSR and C/N during 2^nd sampling; and AS, TN, SOM, pH, EC, Ca and C_mic during 3^rd sampling. NMB registered higher IC, Mg, Na, K, C_mic and BSR during 1^st sampling; AS and C/N during 2^nd sampling; and TN, SOM, pH, EC and Ca during 3^rd sampling. Control did not vary significantly over time due to the absence of perturbation. Overall, a comparison of the pre-fire treatments showed that NMB was the practice that had the least negative effects on the soil properties studied, followed by M15B, and that fire severity was highest at M05B due to the accumulation of dead plant fuel.