Soil biogeochemical and hydraulic property response to wildfire across forested ecosystems of the Santa Catalina Mountains, Arizona, USA

Climate-driven changes in fire-activity have increased area burned and fire severity across western North America. Fire effects on vegetation, soils, and hydrology are particularly important, as they regulate post-fire recovery and ecosystem stability and function. For these reasons, improved understanding of the effects of fire on soil resources is critical to managing and conserving ecosystems. This study focused on fire effects on soil biogeochemical and hydraulic properties, including field-saturated hydraulic conductivity (Kfs) and sorptivity (S), across Madrean Pine Oak, Ponderosa Pine Evergreen Oak, and Mixed Conifer Ecological Response Units (ERU) in the Santa Catalina Mountains, Arizona, USA. The objective was to assess changes in soil properties over time after the most recent fire in the summer of 2020. Measurements were made across 35 sites one- and three-years’ post-fire in sites that experienced varying soil burn severity. Soil nutrient availability, including nitrate and ammonium and phosphorus, increased in concentration with increasing soil burn severity one year after fire, and decreased to values similar to unburned sites three years post-fire. In contrast, Kfs and S increased with soil burn severity in the Ponderosa Pine Evergreen Oak ERU, while the opposite response occurred in the Mixed Conifer and Madrean Pine Oak ERUs. Models indicated that soil water repellency was the most critical parameter controlling Kfs and S the first-year post-fire, but that its influence decreased over time. The different observed responses in soil properties across ERUs point to the need for further research relating plant species composition to post-fire soil recovery trajectories.