AT WHAT DEPTH ARE THE PROPERTIES OF A GYPSEOUS FOREST TOPSOIL AFFECTED BY BURNING?

Wildfires represent one of the main factors of land degradation in Mediterranean environments having negative effects to several ecosystem services. In this work, the fire-induced changes associated with depth (O horizon and Ah at 0-1, 1-2 and 2-3 cm depths) were studied in a gypseous soil under Aleppo pine forest. Topsoil monoliths were burned in an outdoor combustion tunnel simulating a fire of moderate intensity. In the O horizon, burning caused an immediate and significant decrease in water repellency (WR), total organic carbon (TOC) and pyrolyzed carbon (PyC) and an increase in total inorganic carbon. The Ah horizon was also significantly affected by fire, but mainly in its first shallower centimetre and with a different direction according to soil properties: TOC, gypsum, WR and PyC decreased, whereas soil aggregate stability and pH increased. Soil burning not only involved the loss of the pre-fire organic matter content of the O horizon and the upper centimetre of the Ah horizon but also decreased their relative abundance of markers of resins, lignin and polysaccharides. Moreover, the soil burning exerted the cracking of alkylic long-chain molecular series, some of them until the 2 cm Ah depth. The reduction of organic lipophilic molecules in the upper soil centimetre may be related to the fire-induced decreases in WR. Moderate burning of the studied gypseous ochric horizon does not modify any of the properties studied at depths greater than 2 cm. Copyright (C) 2013 John Wiley & Sons, Ltd.