The preserve is a rich mosaic of vegetation types, including extensive mixed hardwood forest – a blend of oaks, madrone, California bay laurel, and big leaf maple. In a healthy state, this forest type tends to be resilient to fire; however, as is common throughout the North Bay Area, understory encroachment and crowding by shade-tolerant Douglas fir was widespread. Because of this, we were concerned about potential impacts to biodiversity and habitat functionality as well as the density of ladder fuel material that the encroaching Douglas fir saplings had introduced to the forest. 

In 2020, the preserve and the surrounding area burned in the Glass Fire, with variable fire effects across the preserve, tied largely to variations in vegetation type and topography.

The preserve’s oak woodlands and mixed hardwood forests were only lightly affected by the fire. However, low-severity fire effects in these stands meant that the Douglas fir saplings in the understory were killed by the fire but not burned. This left a dry, highly combustible layer of ladder fuel that could pose a threat to the larger live trees during future fires. To protect these oak woodland stands in the event of another wildfire, our highest priority was to remove the hazardous dead Douglas fir fuel accumulation, and to create conditions that would support ecological objectives during planned future prescribed and cultural burning. 

We designed this project to include 120 acres of understory thinning and two shaded fuel breaks. We used a combination of field observation and remotely sensed data to target areas with dense ladder fuels, high understory mortality, and healthy overstory canopy for thinning. The shaded fuel breaks were designed to improve road user safety and fireline defensibility, and to serve as anchors for a series of future prescribed burn units.

Planning this project involved input from a Wappo Tribal liaison, a Registered Professional Forester, a prescribed fire specialist, and Ag + Open Space staff with expertise in fire and vegetation ecology, as well as coordination with Cal Fire and watershed community groups. While hazard fuel reduction for overstory tree protection was a primary objective, it was important to us to balance this with a suite of other values, including overall forest health, protection of sensitive and culturally important species, carbon sequestration and climate resilience, biodiversity enhancement, soil health protection, and community safety, and with an eye towards restoring conditions appropriate for Indigenous access and stewardship. To that end, the project team decided on a prescription of removing both dead material and live Douglas fir up to ten inches in diameter, with additional work to remove lower conifer limbs within shaded fuel break corridors and with a number of resource protection measures and site-specific nuances incorporated. These included:

• Surveying all project areas for cultural resources, special-status species, breeding/nesting birds, trees that could support hibernating or maternally roosting bats, and culturally important or locally unique plant and fungi populations, and establishing protection buffers around these to ensure that physical impacts and noise – as relevant – were avoided or mitigated during project implementation.
• Choosing to treat slash primarily by pile burning, with pile construction prohibited in sensitive areas to avoid impacts to certain plants and fungi.
• Making use of hand crews only, with no off-road driving or equipment use allowed in order to protect fragile, fire-affected soils.
• Instructing crews to protect and retain young hardwoods to allow for their recruitment into the canopy, provide shading within shaded fuel breaks, and support healthy forest structure with a variety of age classes.

Overall, we’re pleased with the results of this project so far. The treated stands support a rich variety of native understory plants, young trees, and rare plant populations, and contain minimal slash fuels. Forest stand structure is ecologically appropriate for this vegetation type and appears conducive to keeping future fire on the ground and out of the trees. 

Every project offers opportunities to learn and to refine. We found that it’s important to keep written prescriptions (or instructions) for the fuels crews as simple and clear as possible, and to provide training on pile construction and location to crews who may not have experience with pile burning and expected flame heights. While targeting trees up to ten inches in diameter effectively removed most of the hazard fuel accumulation, the project area contained quite a few live Douglas fir that were just over the ten-inch cutoff but not yet established as overstory trees which probably should have been removed at the same time.  Unexpected benefits included crews with strong botanical identification skills who improved the project by finding new invasive species and rare plant populations, and electric saws which minimized noise and emissions. The project has also proved fruitful in terms of connecting with our conservation partners and community.

Ag + Open Space values collaboration as a means to strengthen community bonds, improve the landscape-scale functionality of vegetation management projects, and provide channels for knowledge sharing and data collection. This project created opportunities for us to connect with community groups, Tribal partners, and neighboring landowners; support Cal Fire’s strategic objectives; and engage with the public via a series of educational outings. We’re fortunate to have an ongoing partnership with Sonoma State University, where the Saddle Mountain Preserve and this project area serve as a study site for measuring and tracking forest stand structure changes in response to both wildfire and mechanical thinning. Our hope is that this research will strengthen our collective understanding of landscape response to fire and effective fuels management within our region.