Fuel Complex Alterations Associated with Spruce Beetle-Induced Tree Mortality in Intermountain Spruce-Fir Forests, USA
Tree mortality caused during extensive outbreaks of spruce beetle (Dendroctonus rufipennis Kirby [Coleoptera: Curculionidae]), has been assumed to increase hazardous fuel loads and consequently influence fire behavior, occurrence, and effects. However, little research has been done to quantify or qualify how spruce beetle-induced tree mortality may alter fuel complexes during the course of an outbreak. The objective of our research was to determine how fuel complexes differ between stands with 1) endemic populations of spruce beetle, 2) stands experiencing current outbreaks and 3) stands with post-outbreak spruce beetle-induced tree mortality. We measured ground, surface and aerial fuels in spruce-fir stands assigned into one of three spruce beetle condition classes; endemic, epidemic, or post-epidemic. These stands were located on the Manti-LaSal and Fishlake National Forests in south central and southern Utah. We used analysis of variance to compare mean differences in stand attributes and fuel variables between the three spruce beetle condition classes. Mean amount of down, woody, surface fuel (tonnes/ha) in the 100 hr size class in epidemic stands was significantly greater than endemic stands. Mean litter depth and amount was significantly greater in epidemicstands than endemic and post-epidemic stands. A significant increase for most estimates of live and dead herbaceous material was detected in epidemic stands and post-epidemic stands when compared with stands not impacted by spruce beetle. Similarly, significant increases in live shrub material were detected in post-epidemic stands. Spruce-fir stands also had significantly less live aerial fuels following outbreaks compared with endemic stands.
Jorgenson, C.A., and M.J. Jenkins. 2010. Fuel Complex Alterations Associated with Spruce Beetle-Induced Tree Mortality in Intermountain Spruce-Fir Forests, USA. For. Sci. 56:In press.