Wildfire Impacts on Soil-Erosion and Hydrology in Wet Mediterranean Forest, Portugal

Abstract

The Agueda Basin, north-central Portugal is comparatively wet (rainfall, 1600-1800 mm/yr) with frequent, relatively large storms in autumn and winter yet the summer drought is sufficiently long and consistent for frequent forest wildfires. This paper discusses wildfire impacts in such a wet Mediterranean environment on soil hydrophobicity, infiltration capacity, overland flow coefficients, soil loss, rainsplash detachment and small-scale ground level changes for Eucalyptus globulus and Pinus pinaster forest: (1) 0-2 years after fire ('new' burn); (2) 3-4 years after fire ('old' burn); and (3) 'mature' (or long unburnt) sites. For 'new' burn sites, rainsplash detachment rates are an order of magnitude and soil losses two orders of magnitude higher than for 'old' burn sites and both are two orders of magnitude higher than for 'mature' sites. Soils are hydrophobic in all three categories of sites, but infiltration capacities are lower at 'new' burn and 'old' burn than at 'mature' sites. Overland flow coefficients on long unburnt sites were low while on burnt sites they were high and tended to be higher for summer and autumn than for winter and spring, implying enhanced hydrophobicity under summer drought conditions, causing decreased infiltration capacity and increased overland flow. The distinctiveness of fire effects on soil erosion and hydrology in this wet Mediterranean environment and implications for post-fire management are discussed.

Soil Erosion Under Different Land Use and Cover Types in a Marginal Area of Portugal

“…This rising trend, although including some periods of lower burnt area, distinguishes Portugal from the other southern Member States with the highest burnt areas, particularly in the central and northern regions. It is commonly accepted that fire increases runoff and soil erosion (Benavides-Solorio & MacDonald, 2005;Cerdà & Doerr, 2005;Cerdà & Lasanta, 2005;Coelho et al, 2004;Ferreira et al, 2005Ferreira et al, , 2008Shakesby et al, 1993Shakesby et al, , 1996Shakesby et al, , 2002. Increased erosion after forest fire stems primarily from the destruction of vegetation and changes in the soil physical and hydrologic properties that reduce infiltration rates and increase availability of loose sediment (Ferreira et al, , 2008.…”

Salvage harvesting – past lessons and future issues

“…Work to date indicates that salvage logging may: • Reduce or eliminate biological legacies such as large trees with cavities and large logs and coarse woody debris (Hutto 1995, Lindenmayer et al1997, Nappi et al 2003; • Modify or destroy rare and diverse post-disturbance habitats (Franklin et al 2005); • Influence populations of some species and alter community composition (Morissette et al 2002); • Impair natural vegetation recovery (van Nieuwstadt et al 2001); • Facilitate the colonization of invasive species (Beschta et al 1995(Beschta et al , 2004); • Alter soil properties and nutrient levels and increase erosion (Shakesby et al 1993(Shakesby et al , 1996); • Modify hydrological regimes and aquatic ecosystems (Minshall 2003, Karr et al 2004; and • Alter patterns of landscape heterogeneity (Radeloff et al 2000, Mackey et al 2002.…”

Assessment of post fire debris flow potential in a Mediterranean type ecosystem

“…Burning intensity significantly affects soil erosion processes because it determines the extent of destruction of the vegetation cover, the depth of heat penetration and the temperature gradient into the soil during wildland fires [8]. The loss of plant cover and of litter layer expose the soil to the increased kinetic energy of raindrops, which in turn favour the runoff production, soil detachment, raindrop splash and sediment yield [9] Debris flows are produced frequently in response to summer convective thunderstorm activity over drainage basins burned by wildfire [10]. Debris flows pose a hazard distinct from other sediment-laden flows because of their unique destructive power; debris flows can occur with little warning and can exert great impulsive loads on objects in their paths.…”