To date, the most commonly used operational wildland fire behavior prediction models have been derived from semi-empirical relationships that assume a steady spread rate in homogeneous surface fuels (Mell et al. 2007). Forests, however, are heterogeneous in species composition, structure and physical and chemical condition. Our proposed project explores changes in fuel moisture, monoterpenes and combustibility in Rocky Mountain forest conifers resulting from bark beetle infestations. We will work with Douglas-fir, lodgepole pine and Engelmann spruce, all widely distributed conifers that have experienced unprecedented levels of bark beetle mortality in the past two decades in the Intermountain West. We will sample four crown condition classes for each tree species (G = Green, healthy and unattacked; GI = green, but currently infested; Y = yellow, previous years infestation; and R=red, two to four years post-infestation). Each crown condition class will be tested for foliar moisture and monoterpene levels and compared for significant changes and/or correlations in the two parameters. The effect of altered foliar moisture and monoterpene levels will be evaluated in a series of laboratory flammability tests. Values corresponding to the field and laboratory results will be used to run the Wildland Urban Interface Fire Dynamic Simulator (WFDS) to demonstrate how outputs can affect a physics-based model of fire spread. The study proposed here represents a unique opportunity to provide fundamental information on the wide range of foliar moisture/monoterpene values of conifer foliage observed in nature. Research will characterize how changes in foliar moisture content, and the kind, quality and quantity of volatile monoterpenes affect fire spread modeling. Dr. Jenkins, his collaborators and students have done much of the fundamental research on the impact of bark beetles on fuels and fire behavior in Intermountain conifer forests (Page and Jenkins 2007 a and b; Jenkins et al. 2008; Jorgensen and Jenkins 2010; Jorgensen and Jenkins in review). Dr. Runyons research focuses on the chemical ecology of interactions between organisms and their environment to explain patterns we see in nature. The work proposed here will use this research foundation to further the understanding of fire spread across heterogeneous landscapes. The PIs will employ a doctoral student, a research technician and field technician and utilize the laboratories and computing facilities in the Department of Wildland Resources at Utah State University and the USDA Forest Service, Rocky Mountain Research Station, Forestry Sciences Lab in Bozeman to conduct the research. The research team is fully capable of executing the proposed research which will result in the production of four peer-reviewed manuscripts and a doctoral dissertation. Funding for the proposed research is requested for three years in the total amount of $419,569.00 including indirect costs. The majority of the requested funding is for salary and wages for non-federal employees and travel to field locations in the intermountain region.