Soil Structural Degradation During Low‐Severity Burns

Abstract

AbstractLow‐severity wildfires and prescribed burns have been steadily increasing for over three decades, currently accounting for more than half of total burned area in the southwestern United States. Most observations immediately after low‐severity burns report little adverse impacts on soil properties and processes. In a few studies, however, significant deterioration of soil structure has been observed several months after such fires. Here we show that rapid vaporization of pore water during low‐severity burns raises pneumatic gas pressure inside large aggregates (20–30 mm) to damaging levels, on the order of aggregate tensile strength and high enough to cause viscoplastic deformation. However, the impact on soil structure was not immediately perceptible. This suggests that other natural forces, such as wetting‐drying and thermal cycles, are required to disrupt the weakened aggregates. Thus, adverse consequences of the suggested mechanism on soil processes and services (e.g., infiltration, erodibility, and organic matter protection) are likely overlooked.