More info for the terms: cover, fire frequency, fire-return interval, frequency, fuel, lichen, lichens, moderate-severity fire, root crown, shrubs, tree
Fire adaptations: Dwarf birch regenerates after low- and moderate-severity fire by sprouting from the root crown and rhizomes [72]. The samaras are dispersed by wind and can invade burned areas from off site [4]. Successful establishment from seed, however, is rare in dwarf birch [18,28,98].
FIRE REGIMES: Dwarf birch is adapted to a wide range of FIRE REGIMES, from subarctic and alpine areas that seldom burn to boreal environments that burn frequently [22,24]. Black spruce-birch (Betula spp.) is the most widespread forest type in interior Alaska and also the type with the highest frequency of fire [91]. Native Americans were an important cause of fires in the black spruce-birch ecosystem [59]. Fire frequency increased with the increase in mining activity in the 1800s [89]. Today, most fires are lightning caused [39,58]. Between 1940 and 1969, lightning was responsible for 78% of the area burned in interior Alaska [89].
Fires occur in interior Alaska between 1 April and 30 September. Most fires occur in May, June, and July, corresponding with the highest annual temperatures, longest day length, lowest humidity and precipitation, and high winds [32,89]. Fires can occur, however, whenever fuels are not covered with snow and are exposed to sufficiently warm temperatures and drying winds [89].
Fire years are sporadic in occurrence but tend to occur at least once every decade [40]. ÂExceptional fire years are characteristic of the black spruce-birch ecosystem. In Alaska, 6 years (1941, 1950, 1957, 1969, and 1977) accounted for 63% of the total area burned between 1940 and 1978 [93]. The average acreage burned each year in interior Alaska is approximately 1 million acres [59]. Fires tend to be large and may spread over thousands to hundreds of thousands of acres or more [40,57,87].
Estimated fire-return intervals in the black spruce-birch ecosystem vary from 50 to 200 years [40,93]. Fires occur every 50 to 70 years in black spruce-white spruce/bog birch/reindeer lichen communities in interior Alaska [32]. Heinselman [40] estimates a fire-return interval of 130 years for open black spruce/reindeer lichen forest and 100 years for closed-canopy black spruce forest. Mean fire-return intervals in lowland black spruce forests on the Kenai Peninsula, Alaska, range from 89 to 195 years [2,60].
Black spruce-birch communities experience high-severity, stand-replacing fires. These communities are highly flammable due to the abundance of ericaceous shrubs, the prevalence of dead, low-hanging branches on the black spruce trees which are often covered with highly flammable epiphytic lichens, and the thick moss and lichen mats that cover the forest floor and become highly flammable after periods of low rainfall [57,58,90]. There is often nearly continuous fuel from the forest floor to the tree crowns [93]. Most fires in black spruce-birch communities are either crown fires or ground fires severe enough to damage or kill aboveground vegetation, including overstory trees. Fires may be severe enough to completely expose the mineral soil layer [26,40,87,93].
The following table provides fire return intervals for plant communities and ecosystems where dwarf birch is important. For further information, see the FEIS review of the dominant species listed below.
Fire-return intervals for plant communities with dwarf birch Community or Ecosystem Dominant Species Fire Return Interval Range (years) birch Betula spp. 80-230 [82] tamarack Larix laricina 35-200 [68] black spruce Picea mariana 35-200 conifer bog* Picea mariana-Larix laricina 35-200 jack pine Pinus banksiana <35 to 200 [19,26] aspen-birch Populus tremuloides-Betula papyrifera 35-200 [26,94] *fire return interval varies widely; trends in variation are noted in the species review
