Role of Vegetation Loss in Post-Fire Geomorphic Response

Increases in runoff and erosion following wildfire are commonly attributed to fire effects on soil properties and consumption of vegetative matter – canopy, litter, and duff. Research emphasis on soil effects as primary cause of process acceleration results in limited understanding of the effects of vegetative losses on hydrogeomorphic response. Increases in overland flow and associated soil entrainment are attributed to reduced infiltration capacity brought about by water-repellent soils, pore clogging by ash and char, and other soil-related factors. Yet recent studies report high spatial variability in water-repellent layers and question the relevance of hydrophobicity in accelerated runoff response. Other studies demonstrate strong spatial association between occurrence of debris-laden flows and remote-sensed indicators of loss of vegetative cover without regard for soil effects. Intact vegetative matter attenuates and stores mass and energy delivered as rainfall. Especially in environments with steep, forested hillslopes where wildfires commonly occur, there has been limited consideration of the consequences to runoff and erosion when delivery of mass and energy is accelerated due to vegetation loss. Infiltration capacity may simply be overwhelmed independent of fire-induced soil changes. First principle analysis, computer modelling, and lab experiments establish theoretical foundations for quantitative partitioning of the effect of vegetation consumption by fire on post-fire hydrogeomorphic response. The results set foundations for detailed field studies. Better understanding of the role of vegetation loss is expected improve burned area assessment procedures and post-fire hazards prediction.