Spruce Beetle-Induced Changes to Engelmann Spruce Foliage Flammability
Intermountain Engelmann spruce (Picea engelmannii Parry ex Engelm) stands affected by the spruce beetle (Dendroctonus rufipennis Kirby) represent a unique and growing fuel complex. In this study, we quantified and compared the changes in moisture content, chemistry, and flammability of foliage from trees in three crown condition classes: unattacked (green [G]), currently mass attacked (green-infested [GI]), and mass attacked the previous year (yellow [Y]) over the course of a fire season. GI trees displayed highly variable decreases in moisture content both between trees and within individual tree crowns that produced variable increases in flammability. The foliage on Y trees had significantly lower moisture contents, higher proportions of lignin and cellulose, and lower proportions of carbohydrate-based compounds than G foliage, which resulted in increased flammability. This increase in crown flammability was short-lived because the foliage on Y trees dropped abruptly approximately 14 months after mass attack (by late July). Given the observed changes in flammability, increased crown fire potential may occur in spruce beetle-infested forests during the spring when G and Y foliage flammability is highest, provided sufficiently dry conditions, and in late summer when the combination of peak GI foliage flammability coincides with the peak in seasonal drying.
Page, Wesley G., Jenkins, Michael J., Runyon, Justin B. 2013. Spruce Beetle-Induced Changes to Engelmann Spruce Foliage Flammability. Forest Science.