Bark Beetles, Fuels, Fire Potential and Nitrogen Cycling in Contrasting Conifer Forests of Greater Yellowstone

Abstract

Recent increases in insect and fire activity throughout the western US have presented forest managers with formidable challenges. The extent and severity of bark beetle (Curculionidae: Scolytinae) epidemics have reached unprecedented levels, and the number of large, severe fires continues to increase. These trends are expected to continue because climate change is implicated for both disturbances. Insects and fire have tremendous ecological and economic effects in western forests, yet surprisingly little is known about how fire hazard may change following bark beetle epidemics, and the efficacy of alternative forest management practices (e.g., removal of beetle-killed trees or remaining small trees) designed to reduce future fire hazard is largely unknown. We are employing a combination of field studies, remote sensing and simulation modeling to understand how bark beetle infestation affects fire hazard in two widespread but contrasting forest types, lodgepole pine (Pinus contorta) and Douglas-fir (Pseudotsuga menziesii). Lodgepole pine and Douglas-fir forests are key components of Rocky Mountain landscapes, and both are experiencing extensive and severe bark beetle outbreaks. Published research on beetle effects on fire in lodgepole pine forests is inconclusive, and almost no studies have examined Douglas-fir. We hypothesize that differences in fire regime, stand structure, regeneration potential and decomposition of woody fuels lead to important differences in fuel profiles, fire hazard and, in turn, the effectiveness of alternative mitigation strategies in lodgepole pine and Douglas-fir. We also anticipate that ecosystem responses, especially nitrogen cycling, to beetle attack will differ between these two forest types. Our studies are being conducted in Grand Teton and Yellowstone National Parks, and the Bridger-Teton and Shoshone National Forests within the Greater Yellowstone Ecosystem (GYE), where we build on >20 years of research and our recent studies of bark beetles and fire in lodgepole pine forests. During the summer of 2010, we conducted a significant portion of the field component of the project, measuring stand structure and fuel profiles in a chronosequence of Douglas-fir forests of differing time since beetle attack (TSB), and also measuring burn severity and forest regeneration following a 2008 fire that burned a recently beetle-attacked forest. Data analyses are ongoing and results will be forthcoming.