During periods with epidemic mountain pine beetle (Dendroctonus ponderosae Hopkins) populations in lodgepole pine (Pinus contorta
Dougl. ex Loud. var. latifolia Engelm.) forests, large amounts of tree foliage are thought to undergo changes in moisture content and chemistry brought about by tree decline and death. However, many
of the presumed changes have yet to be quantified. In this study, we quantified and compared fuel moisture, chemistry, and resulting flammability of bark beetle affected foliage in terms of ignitability, combustibility, consumability, and sustainability at a site in far eastern Idaho, USA.
Results revealed substantial decreases in moisture content, the proportion of starches and sugars, and crude fat and increases in the proportions of lignin, cellulose, and hemicellulose in foliage of trees attacked in the previous year (yellow foliage) or more than two years previously (red
foliage). Increases in emission rates of several terpenes that were correlated with flammability were also detected in yellow foliage. The flammability of fresh yellow and red foliage increased with regard to ignitability and sustainability, with shorter times to ignition, lower temperatures
at ignition, and higher heat yields when compared with unattacked green foliage. Our results confirm the overwhelming importance of fuel moisture on flammability and suggest that fuel chemical composition also has significant effects on lodgepole pine foliage flammability.
Department of Wildland Resources, Utah State University, 5230 Old Main Hill, Logan, UT 84322, USA. 2:
Rocky Mountain Research Station, USDA Forest Service, 1648 South 7th Avenue, Bozeman, MT 59717, USA.
Publication date: August 31, 2012
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