RES 2025054 - Laserfiche WebLink

Vegetation Overview of Vegetation Within the WUI Vegetation is the fuel of wildfire, and three vegetation factors influence fire behavior: 1) Volume of vegetation. The volume of vegetation determines how much fuel is available for the wildfire, influencing the maximum intensity and duration of the burn. 2) Arrangement of vegetation. The arrangement of the vegetation also influences fire intensity because taller vegetation can produce greater flame lengths leading to a higher intensity burn. The arrangement of vegetation also influences what type of fire can occur, as continuous vegetation from the surface to the tree canopy can provide pathways for fire to move into the tree crowns, causing burning of small groups of trees or crown fires. 3) Surface Area to Volume Ratio. The surface area to volume ratio influences how readily vegetation ignites and burns and how long it burns. `Lighter' vegetation, like grass, has a low surface area to volume ratio and readily ignites when the grass blades are entirely yellow and fully dried out. This low surface area to volume ratio also results in fire quickly consuming the grass, and there is little residual fire after the main front of the fire has passed. `Heavier' fuels like logs have a higher surface area to volume ratio and take longer to ignite and burn, but once ignited, they burn longer. Vegetation and Development Within WUI Area 1 The vegetation in WUI Area 1 alongthe City's west side is characterized by a generally continuous band of Oak forest and woodlands. On the lower slopes, the tree canopy tends to be more open, consisting of individual trees or clusters of trees separated by openings in the tree canopy, while in the middle and upper slopes, the canopy tends to be more dominated by more closed forests and woodlands. Surface vegetation on the lower slopes is a mix of grasslands with areas covered with shrublands. Beneath the areas covered by tree canopy, small trees are also present. Understory vegetation on the middle and upper slopes comprises a dense layer of shrubs and small trees. On the upper portions of the slope, there is little to no separation between the surface vegetation and the tree canopies. The extent of development up the slopes in WUI Area 1 varies. Generally, the development consists of low-density (more than 100 feet between homes) single-family home communities separated by undeveloped areas containing continuous natural vegetation (e.g., oak woodlands, grasslands, etc.). Landscaping within these communities combines frequently maintained ornamentals (e.g., irrigated lawns, flower beds, etc.) and managed oak woodlands. There is sufficient vegetation within these communities to sustain the spread of a fire, though not at the same intensity as the adjacent natural areas, due to lower fuel volumes and better separation between tree crowns and surface vegetation. West of Foothill Road, there are no substantial barriers to fire spread, such as large, fully developed areas or wide roads (more than 100 feet wide) that would act as a barrier to fire spread on the hillsides west of Foothill Road. The area East of Foothill Road in WUI Area 1 is generally more densely developed, consisting of higher -density residential communities with less than 30 feet between homes and commercial buildings with large paved parking areas. This area contains many fewer open space areas with continuous natural vegetation. The areas where a wildfire could spread east of Foothill Road are much more limited because there is less flammable vegetation, and it is separated by areas of non-combustible pavement or maintained landscaping. APPENDIX A -WILDFIRE 12 of 219