Post-fire recovery of soil organic matter in a Cambisol from typical Mediterranean forest in Southwestern Spain

8 páginas.-- 2 figuras.-- 3 tablas.-- 31 referencias.-- Supplementary data associated with this article can be found in the online version, at doi:http://dx.doi.org/10.1016/j.scitotenv.2016.02.134 These data include the Google map of the most important areas described in this article.

Wildfire is a recurrent phenomenon in Mediterranean ecosystems and contributes to soil degradation and desertification, which are partially caused by alterations to soil organic matter (SOM). The SOM composition from a Cambisol under a Mediterranean forest affected by a wildfire is studied in detail in order to assess soil health status and better understand of soil recovery after the fire event. The soil was sampled one month and twenty-five months after the wildfire. A nearby unburnt site was taken as control soil. Soil rehabilitation actions involving heavy machinery to remove burnt vegetation were conducted sixteen months after the wildfire. Immediately after fire the SOM increased in topsoil due to inputs from charred vegetation, whereas a decrease was observed in the underlying soil layer. Twenty-five months after fire soil-pH increased in fire-affected topsoil due to the presence of ashes, a decrease in SOM content was recorded for the burnt topsoil and similar trend was observed for the water holding capacity. The pyro-chromatograms of burned soils revealed the formation of additional aromatic compounds. The thermal cracking of long-chain n-alkanes was also detected. Solid-state 13C NMR spectroscopy supported the increase of aromatic compounds in the fire-affected topsoil due to the accumulation of charcoal, whereas the deeper soil sections were not affected by the fire. Two years later, soil parameters for the unburnt and burnt sites showed comparable values. The reduction of the relative intensity in the aromatic C region of the NMR spectra indicated a decrease in the charcoal content of the topsoil. Due to the negligible slope in the sampling site, the loss of charcoal was explained by the post-fire restoration activity, degradation, leaching of pyrogenic SOM into deeper soil horizons or wind erosion. Our results support that in the Mediterranean region, fire-induced alteration of the SOM is not lasting in the long-term.

MA Jiménez-González and NT Jiménez-Morillo thank the Spanish Ministry of Economy and Competitiveness (MINECO) for funding their pre-doctoral FPI fellowships (BES-2014-069238 and BES-2013-062573). The Marie Skłodowska-Curie actions (REA grant agreement No. PCIG12-GA-2012-333784-Biocharisma project), MINECO and the European Development Fund (Projects PCGL2012-37041, CGL2013-43845-P and CGL2012-38655-C04-01) are thanked for the financial support. Marina Paneque Carmona and Marta Velasco Molina are acknowledged for providing technical help during sampling.

Peer reviewed