ESTIMATING RELEASE OF CARBON FROM 1990 AND 1991 FOREST-FIRES IN ALASKA

An improved method to estimate the amounts of carbon released during f ires in the boreal forest zone of Alaska in 1990 and 1991 is described . This method divides the state into 64 distinct physiographic regions and estimates areal extent of five different land covers: two forest types, peat land, tundra, and nonvegetated. The areal extent of each c over type was estimated from a review of topographic maps of each regi on and observations on the distribution of forest types within the sta te. Using previous observations and theoretical models for the two for est types found in interior Alaska, models of biomass accumulation as a function of stand age were developed. Stand age distributions for ea ch region were determined using a statistical distribution based on fi re frequency, which was from available long-term historical records. E stimates of the degree of biomass combusted were based on recent field observations as well as research reported in the literature. The loca tion and areal extent of fires in this region for 1990 and 1991 were b ased on both field observations and analysis of satellite (advanced ve ry high resolution radiometer (AVHRR)) data sets. Estimates of average carbon release for the two study years ranged between 2.54 and 3.00 k g m(-2), which are 2.2 to 2.6 times greater than estimates used in oth er studies of carbon release through biomass burning in boreal forests . Total average annual carbon release for the two years ranged between 0.012 and 0.018 Pg C yr(-1), with the lower value resulting from the AVHRR estimates of fire location and area.