APPENDICES - Laserfiche WebLink

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 torching small groups of trees or crown fires. Finally, 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 fully cured or dried out, and the grass blades are entirely yellow 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. The vegetation in the WUI areas along the 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. Closed-canopy forests and woodlands primarily characterize the middle and upper slopes. 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. How far up the slope development on the west side of the site reaches varies. There are no large developed areas west of Foothill Road that are anticipated to be a barrier to fire spread because there is little or flammable vegetation or offer an area of relative safety because a wildfire is not expected to burn actively there. Generally, the development consists of low-density (more than 100 feet between homes) single-family home communities separated by undeveloped areas. 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. Open-canopy oak woodlands and grasslands characterize the vegetation in the WUI areas along the city's south side. Areas of continuous grassland are common throughout this WUI area. Tree cover is varied, with most areas only having scattered trees within the grasslands. Sheltered areas like drainage bottoms and north-facing slopes generally have denser tree cover. Development in this WUI area is composed of larger planned residential communities with a higher density (less than 30 feet between homes) than the communities along Foothill Road. Vegetation within these communities is predominantly maintained ornamental landscaping. Natural vegetation is limited to isolated strips of vegetation along drainage bottoms or small sections of hillside. The exception to this are the homes along the southern limit of development. These areas have more in common with the communities along Foothill Road and contain ornamental landscaping near the homes and natural areas around the perimeter of the landscaped areas. Tree-Related Fire Hazards Public Trees Public trees within the WUI areas of the City are comprised of trees located along roadways, trees in open space areas, and park trees. Most of the public trees in WUI areas in Pleasanton are located within the more than 700 acres of open space in the City. These trees are further than 100 feet from a structure or 20 feet from a road and are outside of the defensible space area in the LPFD’s vegetation management standard so the City does not regularly maintain them. City- maintained trees within the WUI areas are predominantly located along roadways, with a minor component in City parks. Many native and ornamental tree species present along roadways in the WUI areas are broadleaf trees that do not have characteristics identified by state or local fire agencies as highly flammable. Native Oak (e.g., Coast Live Oak and Valley Oak) and common landscape tree species (e.g., Ornamental Pear and Sweetgum) are identified as ‘fire resistant’ or have a ‘favorable fire rating’ according to state and local wildfire preparedness guides. SubAppendix A contains a list of references for fire-resistant species and fire-wise landscaping. 10