Wildfire effects on soil erodibility of woodlands in NW Spain

Abstract

Knowledge of soil erodibility following wildfire is of crucial importance for prioritisation of post-fire restoration practices for soil erosion mitigation. The present work therefore aims to determine the effect of wildfire on soil erodibility for common woodlands in Galicia, NW Spain. This is done by comparing selected topsoil properties of 28 pairs of recently wildfire-burned and neighbouring unburned sites on different geologic substrates. The soil properties were selected for their supposed importance in erodibility, and include aggregate size distribution and water aggregate stability. Comparison of the burned and unburned sites suggested that wildfire had a noticeable negative effect on aggregate size distribution but not on particle size distribution. The effect on aggregate stability was highly variable. Aggregate stability was clearly lower at the burned than unburned site in about a third of the cases and in the remaining cases either basically the same at both sites or higher at the unburned site. The differences in aggregate stability, like those in aggregate size distribution, appear to be associated with changes in organic carbon content. The impact of wildfire on soil erodibility is supposed to operate through its effect on soil organic matter and, thus, to depend strongly on fire severity. Soil erodibility is then little affected by low-severity wildfires but markedly diminished following high-severity wildfires. All burned topsoils were strongly to very strongly water repellent. Fire-enhaced repellency is therefore viewed as a key factor in the post-fire runoff and erosion processes repeatedly observed in recently burned areas in NW Spain.

Comparing the effectiveness of seeding and mulching+seeding in reducing soil erosion after a high severity fire in Galicia (NW Spain)

“…The mean soil burn severity index was 3.5, with 56.5%, and 33.5% of the area classified in categories 3 and 4, respectively, and 6.5% in category 5. The mean diameter of burned soil aggregates was 0.44 mm, which is considered low for this area (Benito et al, 2009;Varela et al, 2010). Mean soil organic carbon content in burned soils was 9.8%.…”

Molecular characterization of wildfire impacts on organic matter in eroded sediments and topsoil in Mediterranean eucalypt stands

“…The commonly observed increases in runoff and soil erosion in recently burnt areas are typically attributed to the removal of the protective soil cover by vegetation and litter, in combination with heating-induced changes in topsoil properties such as infiltration capacity, aggregate stability and soil water repellency (Badía-Villas et al, 2014a;Granged et al, 2011;Prats et al, 2014;Shakesby and Doerr, 2006;Varela et al, 2010). The combined direct and indirect effects of fires can have important short-to long-term implications for key aspects of soil quality such as the quantity and quality of soil organic matter (SOM), nutrient stocks and pollutants (e.g., polycyclic aromatic compounds), as well as for aquatic habitats receiving sediment-and ash-loaded runoff from upstream burnt areas (Campos et al, 2012;González-Pérez et al, 2004;Smith et al, 2011).…”

Erosion rate predictions from PESERA and RUSLE at a Mediterranean site before and after a wildfire: Comparison & implications

“…The intensity and duration of a fire incident are also one of the controlling factors of forest soil damage (Certini, 2005). Several studies, based primarily on field measurements, laboratory analysis and satellite remote sensing have focused on analyzing the effects of fires on soil properties, functions and processes, including soil erosion (Johansen et al, 2001;Kapalanga, 2008;Mallinis et al, 2009;Varela et al, 2010;Shakesby, 2011;Esteves et al, 2012;de Vente et al, 2013).…”