Minimizing fire hazards in landscapes
Wildfires are a serious hazard throughout much of California where dry, hot weather often prevails. Any type of plant will burn if conditions are suitable.
Plants are injured if temperatures become too high in the canopy or root zone, dehydrating tissues and killing plant cells. When fire is the cause of this thermal injury, it blackens bark in addition to scorching foliage. Wildfire results in one-sided plant injury along edges and distinct boundaries to the burn zone. Lightning strikes can also burn plants, typically isolated or tall trees at higher elevations in eastern and northern California.
Proper maintenance and placement of plants and avoidance of fire-prone species dramatically reduce the likelihood that vegetation fires will burn structures. Building materials, structure type, topography, and other factors are also important in minimizing fire hazards, but only landscape plants are discussed here.
Large plants provide more fuel than small plants and plants present a greater fire hazard the closer they are to structures. Unwatered (nonirrigated) landscapes generally increase the risk of fire.
Provide a defensible space to reduce the risk of structural damage caused by fire. In some areas prone to wildfires, laws require a vegetation-free area around structures; consult local fire officials.
Irrigation. Provide plants with proper cultural care, especially appropriate irrigation to improve plant resistance to fire. Even drought-adapted species may benefit from watering every 1 to 2 months during the dry season, and the increased moisture may decrease their flammability.
Plant placement. In fire-prone areas, keep larger plants farther away from structures and prevent large plants from contacting structures or overhanging roofs. Avoid grouping together a progression of shorter to taller plants; these provide a fuel “ladder,” allowing a ground fire to reach the tree canopies where fire can readily spread from one tree to the next.
Pruning. Properly cut off lower limbs to provide a fuel break between the ground and tree canopies. Prune out dead branches and remove dead or dying plants. Thin crowns (remove some branches) by pruning limbs that form bridges between tall plants.
Sanitation. In fire-prone areas, minimize the buildup of organic litter (bark, leaves, etc.) around trees and structures. Keep flammable mulches well away from homes and other structures.
For more information, consult Home Landscaping for Fire, Landscaping Tips to Help Defend Your Home from Wildfire, and the websites of CAL FIRE and the University of California Center for Fire Research and Outreach.
Adapted from Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide, University of California Statewide Integrated Pest Management Program (UC IPM).