Severe fire activity in the Sierra Nevada is expected to increase by mid-century but was altered by treatment location and extent.

Managing forest resources for resilience is a top priority for the USDA Forest Service. While fuels reduction and restoration can create more resilient forests and reduce fire risk, these activities also might alter the habitat of sensitive old-forest species, such as the spotted owl, and worsen their ongoing declines. Such concerns have slowed the implementation of management activities that might curb stand-replacing fires, including tree thinning and prescribed fire. 

Solving this conundrum involves understanding whether or how the potential negative short-term impacts of restoration on spotted owls can be outweighed by reducing habitat loss to future severe wildfires. To address this question, we developed a novel bioregional-scale severe fire model linked to climate and vegetation (e.g., fuels) conditions that could be used to predict future severe fire activity at fine scales (30-m resolution). We also developed a spotted owl occupancy model linked to forest conditions and severe fire exposure. Both the fire model and the occupancy model were constructed using decades of empirical data.

The fire model produced annual realizations of severe fire occurrence across the Sierra Nevada through mid-century that fed into the occupancy model. The behavior of both models was linked to a factorial design that varied the extent and location of simulated restoration activities. Specifically, treatments either were restricted from spotted owl territories, or were allowed to occur within territories; and under both of these scenarios, treatments were simulated across 20-60 percent of the Sierra Nevada.

Sierra Nevada-wide spotted owl occupancy trajectories for each treatment scenario relative to the baseline no-treatment scenario (dark blue line).

This effort sought to answer two central questions about forest restoration. First, can restoration effectively reduce future severe fire activity in a changing climate? Second, can restoration provide co-benefits to spotted owls?

Key Findings

• Simulated forest restoration had considerable effects to future severe fire activity, reducing severe fire extent by up to 56 percent by mid-century – even under climate warming.
• Allowing restoration to occur in spotted owl territories led to larger reductions in future severe fire (up to 56 percent reduction) compared to when restoration was restricted from owl territories (up to 29 percent reduction).
• When restoration treatments were designed to avoid altering large tree/high canopy cover habitat (key nesting habitat for owls), benefits to owls were immediate and significant.
• When large tree/high canopy cover habitat was modified, owls experienced short-term declines. However, even in these scenarios, the cumulative benefits overcame these short-term costs by mid-century. In other words, restoration treatments always paid off.

Publications

Jones, Gavin M., et al. 2022. Forest restoration limits megafires and supports species conservation under climate change.  Frontiers in Ecology and the Environment.

Additional Resources

• Forest management in spotted owl habitat pays off
• California spotted owls benefit from forest restoration