Graduation date: 2007Recent catastrophic wildfires have forced the forest management community to develop new strategies for reducing forest fuels. Tightly spaced understory trees often create a fire ladder allowing surface fires to encroach into the crowns of overstory trees. This situation can lead to intensive, catastrophic, stand-replacement forest fires. Mechanical removal or mastication of small understory trees is a common approach to promote fire resiliency in the Pacific Northwest. There are numerous limitations and knowledge gaps for managers to select, plan, and implement appropriate technologies to meet sustainable forest management goals involving fuel reduction. Understanding variables such as productivity, soil disturbance, and future fire behavior is essential for accurate and effective decision making. Decisions regarding equipment selection and silvicultural prescription design require forest managers to investigate alternatives from an integrated viewpoint. Therefore, the purpose of this study was to provide forest managers with comprehensive scientific information to aid silvicultural treatment design and machine configuration selection in mechanical fuel reduction treatments. Results from the three overarching topic areas addressed in this dissertation provide significant insight into the relative capabilities and limitations of mechanical forest fuel reduction. Findings from an integrated commercial operation suggest that comprehensive and intensive silvicultural prescriptions may be necessary to favorably alter future fire behavior and to accomplish fuel reduction objectives economically. Additional stand travel necessary to harvest non-merchantable trees did not significantly affect soil physical properties. Non-commercial fuel reduction, employing masticating/mulching treatments proved costly with average costs per acre ranging from $246.62 to $414.07 when residual trees were spaced widely in an uneven-aged ponderosa pine stand. When individual tree selection was used, in dense initial stand conditions, costs per acre ranged from $479.31 to $1,559.79 highlighting the effect of treatment requirements on machine productivity and subsequent costs. The added surface fuel generated during treatment increased surface fire intensity immediately following treatment, based on simulations. This result suggests that follow-up treatments may be necessary for non-commercial approaches to reduce future fire intensity and severity. Discoveries made in this dissertation provide baseline information on approaches to mechanically altering forest fuel and will facilitate decision making by forest managers, landowners, and scientists.