Pyrosilviculture: Combining prescribed fire with gap-based silviculture in mixed-conifer forests of the Sierra Nevada

We used a prescribed fire study to demonstrate the concept of pyrosilviculture, defined here as (i) using prescribed fire to meet management objectives or (ii) altering nonfire silvicultural treatments explicitly in order to optimize the incorporation of prescribed fire in the future. The study included implementation of relatively hot prescribed burns in mixed-conifer forests that have been managed with gap-based silviculture. The fires burned through 12-, 22-, 32-, and 100-year-old cohorts, thus enabling an analysis of stand age influences on fire effects. Mastication and precommercial thinning were assessed as prefire treatments in the 12-year-old stands. Postburn mortality and crown scorch declined with stand age. There was a clear tradeoff between fuel consumption and high rates of tree damage and mortality in the 12-year-old stands. Masticated stands had higher levels of mean crown scorch (78%) compared with precommercially thinned stands (52%). Mortality for all 12-year-old stands was high, as nearly half of the trees were dead 1 year after the fires. Giant sequoia and ponderosa pine had relatively high resistance to fire-related mortality. When applying the concept of pyrosilviculture, there may be opportunities to combine prescribed fire with regeneration harvests that create a variety of gap sizes to sustain both low fire hazard and promote structural heterogeneity and sustainable age structures that may not be achieved with prescribed fire alone.