Forest structure and fire hazard in dry forests of the Western United States

Fire, in conjunction with landforms and climate, shapes the structure and function of

forests throughout the Western United States, where millions of acres of forest lands

contain accumulations of flammable fuel that are much higher than historical conditions

owing to various forms of fire exclusion. The Healthy Forests Restoration Act

mandates that public land managers assertively address this situation through active

management of fuel and vegetation. This document synthesizes the relevant scientific

knowledge that can assist fuel-treatment projects on national forests and other public

lands and contribute to National Environmental Policy Act (NEPA) analyses and other

assessments. It is intended to support science-based decisionmaking for fuel management

in dry forests of the Western United States at the scale of forest stands (about 1

to 200 acres). It highlights ecological principles that need to be considered when managing

forest fuel and vegetation for specific conditions related to forest structure and

fire hazard. It also provides quantitative and qualitative guidelines for planning and

implementing fuel treatments through various silvicultural prescriptions and surfacefuel

treatments. Effective fuel treatments in forest stands with high fuel accumulations

will typically require thinning to increase canopy base height, reduce canopy bulk

density, reduce canopy continuity, and require a substantial reduction in surface fuel

through prescribed fire or mechanical treatment or both. Long-term maintenance of

desired fuel loadings and consideration of broader landscape patterns may improve

the effectiveness of fuel treatments.