This report describes the kinds, quality, amount, and gaps of scientific knowledge for making informed decisions on fuel treatments used to modify wildfire behavior and effects in dry forests of the interior Western United States (especially forests dominated by ponderosa pine and Douglas-fir). A review of scientific principles and applications relevant to fuel treatment primarily for the dry forests (ponderosa pine and Douglas-fir dominated) of the Western United States is provided for the following topics: fuels, fire hazard, fire behavior, fire effects, forest structure, treatment effects and longevity, landscape fuel patterns, and scientific tools useful for management and planning.

More than 80 years of fire research have shown that physical setting, weather, and fuels, combine to determine wildfire intensity and severity. Of these three factors, fuels (vegetation) is the only one that can be treated. The effectiveness and effects of various fuel treatments for restoring dry forests in the Western United States are summarized in this paper. A considerable amount of information is available on fire behavior and the impacts forest structure and fuel modifications have on fire intensity and severity.