Unveiling the effects of fire on soil organic matter by spectroscopic and thermal degradation methods

Wildfires are a global phenomenon occurring in tropical, temperate and boreal regions that affect 300-460 Mha every year (Randerson el al. 2012; Giglio el al. 2013) (Chapter 1). Temperate regions have been affected historically by wildfires (Pausas el al. 2008; Lasheras-Álvarez el al. 2013) and during the 20th century a drastic increase in the extent and severity of burnt areas has occurred. This has made wildfires one of the main threats for ecosystems, particularly those in Mediterranean areas. The obvious consequence of a wildfire is the partial or complete loss of the vegetation. However, wildfires may also cause changes in the physical, chemical and biological properties of soil (González-Pérez el al. 2004; Certini, 2005). The alteration of geomorphological and hydrological processes of the topsoil following a wildfire (de la Rosa el al. 2013a; Faria el al. 2015a) can boost erosion processes that, in turn, are often associated with quantitative and qualitative changes in soil organic matter (SOM) (Chapters 3, 4, 5, 6, 7, 8, 9, 10 and 11). In fact, desertification risk in connection with increased wildfire recurrence is very high in Mediterranean ecosystems (Shakesby, 2011) and the design and application of proper post-fire restoration strategies is paramount for reducing such risk. Restoration of both quality and quantity of SOM is important for soil rehabilitation after a wildfire. Nevertheless, many studies have focused only on the effects of fire in the total amount of SOM, with only scarce the attention paid to the SOM chemical composition and molecular structure, despite its relevance (Almendros el al. 1984a,b; González Pérez el al. 2004, 2008; Certini el al. 2011, de la Rosa el al. 2013a; Faria el al. 2015a,b; Aznar el al. 2016; Jiménez-González el al. 2016; Jiménez-Morillo el al. 2016a, 2017).