Abstract
BackgroundYoung, planted forests are particularly vulnerable to wildfire. High severity effects in planted forests translate to the loss of previous reforestation investments and the loss of future ecosystem service gains. We conducted prescribed burns in three ~35-year-old mixed conifer plantations that had previously been masticated and thinned during February in order to demonstrate the effectiveness of winter burning, which is not common in the Sierra Nevada, California.ResultsOn average, 59% of fine fuels were consumed and the fires reduced shrub cover by 94%. The average percent of crown volume that was damaged was 25%, with no mortality observed in overstory trees 1 year following the fires. A plot level analysis of the factors of fire effects did not find strong predictors of fuel consumption. Shrub cover was reduced dramatically, regardless of the specific structure that existed in plots. We found a positive relationship between crown damage and the two variables of Pinus ponderosa relative basal area and shrub cover. But these were not particularly strong predictors. An analysis of the weather conditions that have occurred at this site over the past 20 years indicated that there have consistently been opportunities to conduct winter burns. On average, 12 days per winter were feasible for burning using our criteria. Windows of time are short, typically 1 or 2 days, and may occur at any time during the winter season.ConclusionsThis study demonstrates that winter burning can be an important piece of broader strategies to reduce wildfire severity in the Sierra Nevada. Preparing forest structures so that they can be more feasible to burn and also preparing burn programs so that they can be nimble enough to burn opportunistically during short windows are key strategies. Both small landowners and large agencies may be able to explore winter burning opportunities to reduce wildfire severity.
Highlights
Young, planted forests are vulnerable to wildfire
Flame lengths were typically less than 1.5 m and increased slightly each day as fuels continued to dry out. These conditions were well within the winter burning prescription that has been developed at Blodgett Forest Research Station (BFRS), which is different than the prescription used for fall burning (Table 1)
Conclusions and management implications The potential logistic, economic, and risk-avoidance advantages of winter burning should be appealing for managers who want to both insulate economic investments and protect future ecosystem services gains that can come from developing mixed species plantations
Summary
Location and forest structural context of prescribed burns Burns were completed in mixed-species plantations at Blodgett Forest Research Station (BFRS) in the mixed conifer forest on the western slopes of the central Sierra Nevada range, which has a Mediterranean climate. From 1994 to 2020, the mean total precipitation during the wet season (further defined below) was 145 cm year−1. A prescribed burn program at BFRS has been active for the past 20 years, during which burns occurred across a variety of seasons, age classes, and silvicultural systems. This is in part due to difficulties obtaining permits to burn during fall and spring windows across the Sierra Nevada region (York et al 2020)
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