Active Fire in the taiga, Manley Fire, 1969. from Naturalist 25 (Special Issue #1), 1974. Photo by Leslie A. Viereck, USDA FS.
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Most forest communities in interior Alaska have been
extensively influenced by recurring fire. Because interior Alaska
tree species have thin bark, even light fires generally result in
extensive tree mortality.
In spite of the lack of detailed data on fire periodicity in Alaska,
several researchers have estimated the length of the fire cycle
in interior Alaska. Viereck and Schandelmeier (1980) estimated that
the natural fire cycle for the Alaska taiga ranges from 50-200 years.
Rowe et al. (1974) estimated the following fire cycles for the Mackenzie
Valley of Canada: 80-90 years for the black spruce type, 30-70 years
for the jack pine type, and 300 years for white spruce stands on
alluvial sites. For the Alaska taiga, Heinselman (1978) estimated
the fire cycle to be 130 years for open spruce-lichen forest and
100 years for closed black spruce. Yarie (1981) reported a fire
cycle of 59.1 years for white spruce, 58.9 years for black spruce,
and only 28.6 years for deciduous tree stands in the Porcupine River
drainage.
Many plants in the Alaska taiga are well adapted to reproducing
themselves after fire. Although black spruce is not fire-resistant,
it is adapted to fire through its semiserotinous cones. Branches
close to the ground, shallow roots, thin bark, and abundant lichens
on lower branches combine to make black spruce especially vulnerable
to death from fire. Cones high in the crown are generally not consumed,
and they retain viable seeds after the fire even though the trees
are dead. Birch and aspen are also well adapted to recurring fires,
both species vigorously reproducing vegetatively following fire.
Additionally both species are prolific producers of light seed which
can be disseminated long distances by the wind.
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Flooding and Other Fluvial Processes
The heavy sediment load of the glacier-fed Tanana River supports
an aggrading system where silt deposition associated with floods
builds terraces of increasing height on the active floodplain. These
fluvial processes, including erosion and silt bar formation, shape
the surfaces on which ecosystem processes take place.
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Click to enlarge. Aerial view of downtown Fairbanks near crest of flood on Chena River, August 15, 1967. Arrow indicates direction of flow of river. from US Geological Survey, Flood of August 1967 at Fairbanks, Alaska. Photograph by the Alaska Railroad.
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