WILDFIRE IMPACTS ON SOIL PHYSICAL PROPERTIES: 2016 ERSKINE FIRE, CALIFORNIA

Wildfires cause significant damage, as can the flooding and debris flows that occur in the aftermath of the fires. Post-fire alterations in soil physical properties and the surface cover influence the landscape years after the fire has passed and have been linked to the occurrence of debris flow events. The 2016 Erskine Fire near Lake Isabella burned over 46,000 acres resulting in a mosaic of burn severity patterns that allowed us to quantify the differences in soil alterations as a function of burn severity. Haake et al. (2017) investigated the same area and found the soil physical properties changed according to the fire’s burn severity. In order to investigate the potential recovery state for the burned soils, we re-collected samples two years later and conducted Atterberg (liquid limit and plastic limit) and shear strength tests and compared them with the previous study. Our results revealed that low burned soils (LBS) and moderate burned soils (MBS) soils had the highest average liquid limit and plastic limit. Plasticity index values decreased as burn severity increased, suggesting that higher burned soils behave more non-plastically and debris flows could easily be triggered during heavy rainfall seasons. Results for shear strength tests revealed that under the lowest normal stress (0.5 TSF), MBS soils had the highest peak shear stress followed by HBS, LBS, and VLBS soils. We see an increasing trend of shear stress as burn severity increases under the highest normal load of 2.0 TSF. Both Atterberg limits and shear strength tests can be influenced by other soil properties such as, organic matter, clay content and the timing of the sampling collection. To see if this is the case, TOC and mineralogy analysis will be conducted on all burn severity classifications. Results for TOC and mineral composition will be presented at the 2020 GSA Cordilleran Section meeting.