Long-term effectiveness of fuel treatments in Whiskeytown, CA

Aims: Fuel reduction treatments are broadly implemented to reduce the risk of extreme wildfire, but research on the long-term effectiveness and impacts of these treatments is lacking. In this study, we examined short- and long-term (2 and 15 year) changes in fuels and understory vegetation after treatment in chaparral and oak-dominated stands. Location: Whiskeytown National Recreation Area, California, USA Methods: Treatments, including hand-thinning, mastication only, burn only, and mastication + burning, were applied randomly to one or two units within each of ten blocks across two vegetation types (chaparral and oak-dominated). Vegetation data was initially 2 years after treatment and remeasured 15 years later with additional sampling of dead surface fuels and shrubs. Fuel and vegetation data were analyzed to examine the effect of treatment, time, and vegetation type. Results: In chaparral stands, hand-thinning, mastication, and mastication + burning reduced shrub height and cover compared to the control. However, only the hand thinning treatment reduced fine woody fuels. Hand-thinning and mastication + burning increased native species richness after two years, but this was also associated with an increase in exotic species richness and cover that persisted after 15 years. In oak-dominated stands, treatments had varied and relatively fewer changes to fuels and vegetation. Shrub height was reduced in both the hand-thinning and burn only treatments, but only mastication reduced shrub cover. Species richness and vegetative cover were largely unaffected by treatment, except for lower native plant cover in mastication and mastication + burning treatments. Conclusion: Treatments varied in their level of effectiveness and most involved trade-offs between their impacts on fuels and vegetation responses that differed by vegetation type. Our findings provide insights for managers interested in balancing these trade-offs when making fuel treatment decisions and emphasize the importance of examining longer-term effectiveness of fuels treatments.