Forest Fire Effects on Soil Phyllosilicates in California

Abstract

Abstract Thousands of hectares of forests are burned annually in wildfires and prescribed burns nationwide. Our objective was to determine the effects of such fires on soil phyllosilicates. At five sites throughout California representing Inceptisols, Andisols, and Mollisols, surface soil samples from similar depths were collected in burned and nearby unburned areas. Fires produced no visible soil alterations except in 1 to 2% of the land area where concentrated fuel such as logs or stumps burned slowly and at higher temperatures, effectively baking the underlying soil. Within the upper 1 to 8 cm at these severely burned areas, kaolin was completely destroyed or substantially depleted and d 001 spacings of clay‐sized vermiculite, chlorite, chlorite‐vermiculite, and hydroxy‐interlayered vermiculite collapsed toward 1.0 nm or were decomposed as shown by x‐ray diffraction. Dehydroxylation of severely burned Fe‐bearing phyllosilicates was indicated by Mössbauer spectroscopy. The decomposition of virtually all phyllosilicates in the upper 2 cm of the soil was observed at one site after burning. The effects of severe burning on the soil phyllosilicates remained clearly expressed at least 3 yr after a fire.