Wildfire in Russian Boreal Forests—Potential Impacts of Fire Regime Characteristics on Emissions and Global Carbon Balance Estimates

Abstract

Most of the research about the effects of the release of carbon and other chemicals to the atmosphere during forest fires focuses on emissions from crown fires or slash fires in which a high percentage of the fine fuels are burned. However, in many temperate and boreal conifer ecosystems, surface fires of varying intensities and severities are an important part of the fire regime. In Russia a large percentage of the area burned in a typical year is in surface fires, which will result in lower carbon emissions than crown fires because of lower fuel consumption. In Russian boreal forest, different distribution patterns of fire severity across the landscape could produce fourfold differences in carbon release. Furthermore, tree mortality after surface fires is often quite extensive, leading to a pulse in carbon release as needles and other fine fuels fall to the ground and decompose. With extensive tree mortality, a decrease in carbon sequestration is expected for several years, until stand level photosynthesis returns to prefire levels. Perhaps the largest potential source of error in estimates of carbon release from biomass fires in Russia is inaccuracy in estimates of burned area. Many published estimates of annual burned area in Russia may be extremely low. On the basis of information on fire return intervals and area of boreal forest, 12 million ha per year may be a reasonable conservative estimate of burned area until better data are available. Based on this estimate, direct and indirect fire-generated carbon emissions from boreal forests worldwide may exceed 20% of the estimated global emissions from biomass burning, making them an important component in understanding global atmospheric chemistry. In considering effects of fire on global atmospheric chemistry, it is important to include the effects of fire severity, postfire mortality, decomposition of fine fuels, and changing postfire vegetation structure as components of fire-induced changes in ecosystem- level carbon flux. But the most important factor may be accurate information on the annual area burned. Levels of carbon storage are likely to be highly sensitive to changes in fire return intervals that result from direct human activities and from climatic changes, making accurate assessments of burned areas and fire severity critical. Strong fire management programs will be key to managing future fire regimes and carbon cycling in Russia’s boreal forest.