Jeff Hatten and Darlene Zabowski. College of Forest Resources, Univ of Washington, Seattle, WA 98195-2100
Soil organic matter (SOM) is altered by fire through combustion, heating and deposition of residues. We examined how classically fractionated soil carbon pools are affected by different levels of fire severity. A model fuel bed of O horizon from a ponderosa pine/Douglas fir forest was burned in the laboratory. Temperature was monitored to determine severity. Humin, humic acid (HA) and fulvic acid (FA) were extracted before and after burning and analyzed for C, H, and N. FA and HA content of the O-horizon decreased with increasing fire severity. FA and HA from 0-1cm A horizon decreased while humin content increased with increasing severity. FA, HA and humin from the 1-2cm A horizon was little affected by the different levels of burning. Fire severity appears to decrease the labile pools of SOM. These changes likely relate to changes in SOM function.