Silviculture and reserve impacts on potential fire behavior and forest conservation: twenty-five years of experience from Sierra Nevada mixed conifer forests

Most administrators and ecologists agree that reducing the levels of hazardous fuels on forests is essential to restore healthy\ud watersheds and protect adjacent human communities. The current debate over the appropriateness, technique, and timing of treatments\ud utilized to restore vegetation structure and composition is currently on-going at local, state, and national levels. To provide\ud information for these forums, the efficacy of seven traditional silvicultural systems and two types of reserves used in the Sierra\ud Nevada mixed conifer forests is evaluated in terms of vegetation structure, fuel bed characteristics, modeled fire behavior, and\ud potential wildfire related mortality. The systems include old-growth reserve, young-growth reserve, thinning from below, individual\ud tree selection, overstory removal, and four types of plantations. These are the most commonly used silvicultural systems and reserves\ud on federal, state, and private lands in the western United States. Each silvicultural system or reserve had three replicates and varied\ud in size from 15 to 25 ha; a systematic design of plots was used to collect tree and fuel information. The majority of the traditional\ud silvicultural systems examined in this work (all plantation treatments, overstory removal, individual tree selection) did not effectively\ud reduce potential fire behavior and effects, especially wildfire induced tree mortality at high and extreme fire weather conditions.\ud Overall, thinning from below, and old-growth and young-growth reserves were more effective at reducing predicted tree mortality