| FIRE SEVERITY
EFFECTS ON SOIL ORGANIC CARBON CONTENT IN ONTARIO’S BOREAL
FORESTS
Category: Climate Change / Carbon Cycling
Jessica Galarza
Trent University
Peterborough, Ontario, CANADA
Boreal forests are one of the largest terrestrial reservoirs
of carbon and fire is a predominant disturbance that influences
the forest and soil structure and composition, and biogeochemical
cycles such as the carbon cycle. Therefore providing reliable
and quantitative information on the level of environmental
change caused by fire is necessary to evaluate the burn severity
effects of fire on soil organic carbon stocks. This study
focuses on identifying burn severity patterns and their effects
on soil organic carbon in two wildfires that occurred in northern
Ontario in 2005. Three field based fire severity classes were
developed. Thirty eight plots where sampled and classified
depending on the severity of the fire. Analyses of the soil
organic matter indicate that one year after the fire, burned
plots had lost carbon when they were compared to control plots
(unburned sites). The most severe fire had lost 3760 g/m2,
and the least severe fire 1170 g/m2. The results suggest that
the field based fire severity classes are related to the lost
soil organic carbon.
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Fire
Severity in Mechanically Thinned Forests of the Sierra Nevada,
California
Category:
Fuel Management
Chad T. Hanson and Dennis Odion
University of California
Davis, California, USA
Much debate has
centered around the effectiveness of thinning as a tool to
reduce fire severity. However, authors recommending such prescriptions
often do not distinguish between precommercial thinning and
the more intensive mechanical thinning, and existing literature
is largely based upon modeling or experimental conditions,
which may not reflect actual management practice. We selected
all areas known to have been mechanically thinned, and then
burned in wildland fire 2000 to present, within national forests
of the Sierra Nevada outside of designated experimental forests.
A total of seven sites within four different fire areas were
located. We compared thinned to adjacent unthinned areas in
terms of fire-induced mortality and combined thinning/fire
mortality, where mortality was measured as a function of basal
area. Our hypothesis was that thinned areas would not differ
in mortality from unthinned areas. Contrary to predictions,
the mechanically thinned areas had significantly higher fire-induced
and combined mortality than the adjacent unthinned areas.
Thinned areas generally burned at high severity, while unthinned
areas burned predominantly at low and moderate severity. Explanations
for the increased severity in thinned areas include inadequate
treatment of activity fuels, enhanced growth of combustible
brush post-logging, and increased mid-flame windspeeds. Mechanical
thinning on these sites appears to have lowered the fire weather
threshold necessary for high severity fire occurrence.
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