Controls on the Spatial Distribution of Near-Surface Pyrogenic Carbon on Hillslopes 1 Year Following Wildfire

Wildfire alters hydrologic and geomorphic systems, promoting increases in runoff and erosion relative to unburned areas. As a result, pyrogenic carbon (PyC) produced by wildfires can experience substantial lateral redistribution from overland flow. Since landscape position helps to determine the fate of PyC, it is critical to understand the geomorphic factors that govern its lateral redistribution as well as the sensitivity of those factors to soil burn severity, which controls the magnitude of many wildfire-induced hydrologic and geomorphic changes. In this study, we quantified the spatial distribution of near-surface (0-5 cm) PyC on three hillslopes roughly 1 year after the 2018 Buzzard Fire in the Gila National Forest, New Mexico, USA. We then use hydrologic monitoring data, terrain analysis, and rainfall-runoff modeling to explain the observed spatial distribution of PyC. Near-surface PyC concentrations decreased from averages of roughly 12-8 g/kg as slope and unit stream power increased by factors of similar to 2 and 4, respectively, on a hillslope burned at low severity. This suggests that susceptibility to runoff-driven erosion was a dominant control on the redistribution of PyC. In contrast, the spatial distribution of PyC in areas burned at moderate to high severity was independent of slope and unit stream power. We attribute this pattern to intense runoff and lack of canopy cover, which promoted erosion of PyC regardless of slope and landscape position. Results demonstrate that how wildfire-induced hydrogeomorphic changes can modulate the importance of terrain attributes in controlling the spatial distribution of PyC in upland landscapes.

Automated summary

Wildfires can alter hydrologic and geomorphic systems, leading to increased runoff and erosion compared to unburned areas, which can result in substantial lateral redistribution of pyrogenic carbon (PyC) through overland flow. The spatial distribution of PyC is influenced by terrain attributes such as slope, unit stream power, and soil burn severity, with runoff-driven erosion being a dominant control factor. In areas burned at moderate to high severity, intense runoff and lack of canopy cover can lead to erosion of PyC regardless of slope and landscape position.