Boreal Forest Fire Regimes And Climate Change

Abstract

Stretching in two broad transcontinental bands across Eurasia and North America, the global boreal zone covers approximately 12 million square kilometres, two-thirds in Russia and Scandinavia and the remainder in Canada and Alaska. Situated generally between 45 and 70 degrees north latitude, with northern and southern boundaries determined by the July 13°C and July 18°C isotherms respectively, the boreal zone contains extensive tracts of coniferous forest which provide a vital natural and economic resource for northern circumpolar countries. The export value of forest products from global boreal forests is ca. 47% of the world total (Kusela 1990, 1992).The boreal forest is composed of hardy species of pine (Pinus), spruce (Picea), larch (Larix), and fir (Abies), mixed, usually after disturbance, with deciduous hardwoods such as birch (Betula), poplar (Populus), willow (Salix), and alder (Alnus), and interspersed with extensive lakes and organic terrain. This closed-crown forest, with its moist and deeply shaded forest floor where mosses predominate, is bounded immediately to the north by a lichen-floored open forest or woodland which in turn becomes progressively more open and tundra-dominated with increasing latitude. To the south the boreal forest zone is succeeded by temperate forests or grasslands.Forest fire is the dominant disturbance regime in boreal forests, and is the primary process which organizes the physical and biological attributes of the boreal biome over most of its range, shaping landscape diversity and influencing energy flows and biogeochemical cycles, particularly the global carbon cycle since the last Ice Age. The physiognomy of the boreal forest is therefore largely dependent, at any given time, on the frequency, size and severity of forest fires. The overwhelming impact of wildfires on ecosystem development and forest composition in the boreal forest is readily apparent and understandable. Large contiguous expanses of even-aged stands of spruce and pine dominate the landscape in an irregular patchwork mosaic, the result of periodic severe wildfire years and a testimony to the adaptation of boreal forest species to natural fire over millennia. The result is a classic example of a fire dependent ecosystem, capable, during periods of extreme fire weather, of sustaining the very large, high intensity wildfires which are responsible for its existence. This chapter presents data on recent and current trends in circumpolar boreal fire activity, with particular emphasis on Canada, Russia and Alaska, and describes the physical characteristics of boreal fires in terms of fuel consumption, spread rates, and energy release rates. The potential impact of a changing climate on boreal fire occurrence and severity, with resultant impacts on atmospheric chemistry and the global carbon budget, is discussed in detail, with reference to current research activities in this area.KeywordsForest FireBoreal ForestBoreal ZoneCrown FireFire WeatherThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.