Soil organic matter alterations resulting from post-fire restoration actions

Burned soils restoration/rehabilitation techniques include tillage, tree logging, reforestation with native or non-native species, and other management. In some cases, restoration may cause additional impacts on soils, producing more severe damages than those caused directly by fire. Triggered soil erosion processes, loss of soil fertility and alterations in the hydrological cycle are among these negative impacts. Analytical pyrolysis (Py-GC/MS) together with graphic interpretation tools like van Krevelen¿s diagram [1] may be used to shed light on alterations caused by burning and restoration plans to soil organic matter (SOM). The objective of this research is to study fire impacts on SOM in a sandy soil under pine (Pinus pinea) forest affected by a severe fire in August 2012 in Doñana National Park (SW Spain). mm) collected from burned adjacent areas before (B) and after restoration practices (BR) (logging and extraction of burned trees). An adjacent unburned (UB) area was used as a control. Bulk soil samples and its fractions were studied by Py-GC/MS and the results were interpreted taking advantage of a van Krevelen diagram using the H/C and O/C atomic ratios calculated from the chemical formulas of compounds as inferred from their mass spectra. The percentage of main compound families obtained by analytical pyrolysis, including alkane/alkene pairs, unspecific aromatic compounds (UAC), peptides, methoxyphenols, fatty acids, carbohydrate-derived, N-compounds and polycyclic aromatic hydrocarbons (PAH), show conspicuous differences among bulk samples from the B, BR and UB control areas. Compared to the UB site, the samples from the B site showed lower proportions of lignin methoxyphenols and increased ones of UAC and PAH. It could be hypothesized that fire produced defunctionalization of methoxyphenols, increasing the proportion of soil recalcitrant compounds. In all cases, the coarse fraction showed a high content of carbohydrate-derived compounds and methoxypheno