Short-term post-fire changes in soil properties and soil suction responses over time in forested soil affecting shallow landslides: field experiments in Nova Friburgo, SE-Brazil

Abstract

Rainfall-induced shallow landslides are frequent hazards in mountainous regions. Although several factors influence their occurrence, the role of fire in triggering such events remains poorly explored, particularly in tropical environments. This study investigated fire as a conditioning factor for shallow landslides through an experimental fire at a 12 m² site covered with degraded Atlantic rainforest. Soil suction was monitored at different depths for two years after the fire at both burned and unburned sites. Soil texture, bulk density, total porosity, organic matter, and true density were analyzed before the fire and 2, 15, and 30 days after, down to 50 cm; bulk density was also assessed at 8 months. Results showed short-term changes in soil properties within 2 days, limited to the soil surface (<5 cm). Changes in soil suction were observed 3 months post-fire in the upper soil and at depth after 6 months. Suction at the burned site was up to five times higher than at the control site. This response is hypothesized to be linked to rapid post-fire vegetation recovery - indirectly observed in the field and through soil temperature data – in addition to the short-term changes in soil properties investigated at the study site. These findings demonstrate that fire can significantly modify parameters critical for slope stability.