Ping, Chien-Lu (University of Alaska, Fairbanks, Palmer
Research Center, Palmer, AK, 99645; Phone: 907-746-9462; Fax: 907-746-2677;
Email: pfclp@uaa.alaska.edu)
C.L. Ping *, E.C. Packee, G.J. Michaelson, Y.L. Shur, J.M. Kimble
Boreal forests cover nearly one-third of the earth’s land surface and store more than 35% of the terrestrial carbon. Generally, drainage has been regarded as the controlling factor for soil organic carbon (SOC) stores in the boreal forest region with C stores increasing with more restricted drainage. However, recent findings indicate surface erosion after forest fire plays an important role in the soil carbon flux. The objective of this study was to evaluate SOC stores along a toposequence and show the relationships among fire, erosion, and SOC fluxes in boreal Alaska. Detailed soil morphological techniques were used to identify buried carbon due to solifluctuation and surface erosion-deposition during the Holocene. Organic C content was measured by a CNH analyzer after inorganic C was removed from the soil samples. Well drained upland soils generally hold 8-20 kgCm-2 but, the poorly drained bottomlands store more than 100 kgCm-2 to a 2 meter depth. Nearly 70% of the C stored in the poorly drained sites are buried and below the modern soil profile. The stratified mineral and organic layers reflect landscape processes. Nearly all buried layers have abundant charcoal particles and charred wood residues that suggest they were deposited after a fire when the vegetation was destroyed and the land surface became susceptible to erosion. The redeposited C and soil layers were than encased in the rising permafrost table. Thus, in the closed basins and valleys of interior Alaska, where boreal forests are the major landcover type, fire-induced erosion becomes an important factor affecting SOC flux. This frozen C will, then, again enter into a more active part of the biogeochemical cycle once the permafrost thaws due to global climate change, fire, or changing land use and then contribute to the greenhouse gas effect.