Monday, November 13, 2006

Fire Severity Effects on the Mineralization of Soil Organic Matter.

Jeff Hatten and Darlene Zabowski. College of Forest Resources, Univ. of Washington, Univ. of Washington, Seattle, WA 98195-2100, United States of America

Forest fire affects the soil organic matter (SOM) pool through combustion, heating and deposition of residues.  Such changes could reduce the decomposability of SOM.  We examined how C mineralization rates of SOM are affected by fire severity using a model fuel bed from a ponderosa pine/Douglas fir forest. Temperature was monitored to determine severity.  O and A horizons were separated and incubated for 180 days.  CO2 efflux was determined using a soda lime trap and cumulative CO2-C released over time was fitted to a double exponential model to determine a labile pool (C0) and the mineralization rates of a labile (k) and a recalcitrant (h) pool.  Preliminary results suggest that as severity increases the mineralization rates of O horizon material decreases.  Mineralization rates from A horizons differ among the different severities depending on deposition of ash and temperature reached during the laboratory burning.  Forest fires may have impacts on the ability of forest soils to sequester carbon.