RES 2025054 - Laserfiche WebLink

4. Tree Management in the Wildland Urban Interface Area The behavior of a wildfire in the City's WUI areas, as described earlier, is influenced by several factors, including the arrangement and volume of vegetation present. The maintenance of this vegetation can significantly impact the spread and intensity of a wildfire. This includes the maintenance of trees on private and public property. Proper tree care in the WUI areas can reduce the risk of extreme fire behavior, including torching (the ignition and rapid burning of individual trees or small groups of trees) or crown fires. The Role of Tree Maintenance in Managing Wildfire Risk Wildfire spread and intensity are dictated by the surface vegetation volume and arrangement. Trees and the tree canopy influence the fire's capacity to transition into and sustain torching or crown fires. Continuous vegetation from the surface to the tree canopy creates a path for fire to spread into the tree canopy. Tree litter indirectly contributes to the spread of wildfire on the surface by adding to the fuel volume on the ground. Therefore, the main fire prevention role of tree maintenance in Pleasanton's WUI areas is minimizing the risk that a wildfire on the surface can spread into the tree canopy. A secondary role would be reducing surface fuel volumes by maintaining leaf litter. Vertical Separation to Reduce Risk of Wildfire Spread into Tree Crowns Tree maintenance recommendations intended to reduce the risk of a wildfire spreading into the tree crowns focus on separating the lighter, more readily ignited leaves and small branches in the tree crown from the surface vegetation that can sustain a wildfire. Vertical separation is created by reducing surface vegetation and raising the height of the lowest branches in the tree crown, which creates space to prevent direct flame contact and allows radiant and convective heat to dissipate.' Creating horizontal space between tree crowns also reduces the risk of a fire transitioning into them by allowing heat and hot gases to vent into the atmosphere and by reducing the risk that flames from one tree torching can come into contact with another tree crown. Tree Litter Maintenance Tree maintenance recommendations for reducing tree litter's contribution to the surface fuel load focus on maintaining the level of accumulated litter at a minimum so that leaf litter cannot contribute to the spread or intensity of a fire. In areas with minimal surface vegetation, particularly areas that serve as a barrier to fire spread( e.g., roads), the focus is on removing any accumulations of litter. Tree Maintenance Standards Trees in the WUI area require maintenance practices to increase horizontal spacing between retained trees to reduce the potential for crown fire spread. These practices remove ladder fuels (i.e., fuel that can facilitate fire spread from ground fuels into tree crowns) by increasingthe vertical spacing between surface fuels (shrubs, grasses) and tree crowns to reduce the potential for surface -to -crown fire transition. 1. The trunks on live, healthy trees take much longer to ignite than the leaves and small branches in the crown. Most wildfires don't burn in an area long enough to ignite the trunk. APPENDIX A -WILDFIRE 18 of 219