Effects of fire on soils

A significant body of evidence suggests that wildfires affect the chemical and physical properties of shallow soils.

Cleveland et al 2019: After a wildfire, there is an increase of nitrate and ammonium put into the soil that can negatively affect an ecosystem. We hypothesized that the soil water in burned areas would have a slightly increased amount of nitrate, ammonium, and pH than the areas unaffected by fire. We took soil samples at Pepperwood Preserve and Crane Creek Regional Park, and extracted the soil porewater to test for nitrate, ammonium, and pH levels. We found that the fire damaged samples had a greater amount of nitrate, ammonium, and pH than the samples that were not burned. 

Vargas and Ortiz 2019:  The Tubbs Fire of 2017 in Santa Rosa, CA partially burned the Pepperwood Preserve oak woodland, chaparral, and mixed evergreen forest at varying temperatures. We investigated the shallow (top 20 cm) soil profiles for visual evidence of fire, including variations in density and color.  Samples were collected across different landscape positions and burn temperatures across varying forest cover types at Pepperwood.  Soil samples were then disturbed and water droplets were administered to the soil surface with a small pipette.  The time to complete water absorption was recorded for each sample. Preliminary results indicate the presence of hydrophobic soil in the higher temperature burn areas, while visual inspection shows an ash layer in the top two centimeters.

Giovanelli et al 2019: Our research investigated the conditions on soil quality post-fire in terms of the ability to foster plant growth. We planted sunflower seeds in collected samples of burnt soil and untouched soil from Pepperwood Preserve, and correlated levels nitrogen and phosphorus to germination rates.

A Watershed Year is a freshman year experience that introduces students to local watersheds as they learn about science. The course focuses on teaching students how to conduct their own research. Course development was funded by National Science Foundation.