Investigating the Effects of Fire on Rooted Pyroclastic Soil Properties by Laboratory Burning Treatments

Abstract

Wildfires increase hillslope instability phenomena by damaging vegetation and altering soil properties. For the present study, a laboratory experimental program was implemented to investigate the physical properties of grass-vegetated pyroclastic soils after their exposure to relatively high temperatures and flames. The soil samples were collected along the Sant’Angelo Creek watershed of the Sarno municipality (Pizzo d’Alvano massif, Campania Region, Italy), which is frequently affected by both wildfires and fast-moving landslides. Owing to the high variability of soil properties (i.e., grain size distribution, porosity, organic matter, root content) in the shallow layers, reconstituted soil samples were tested to different burning treatments to single out the fire-related effects with respect to i) the burning duration and ii) the time passed after the fire. Results reveal that only the near-surface portion of the soil temporarily undergoes significant temperature variations; soil organic matter decreases as the temperature of exposure increases; soil shear strength and soil infiltration characteristics show relevant changes as both the duration of the treatment and the time after the fire increase. The collected information can provide novel insights toward the understanding of post-fire slope stability and erosion.