University of California
Fire in California

Trees

Landscaping trees are often criticized due to the ignition potential they pose to adjacent structures. Non-native trees are especially hazardous as many have burn characteristics that exacerbate the ember volume or hear emitted during combustion. Properly positioning and maintaining trees can help minimize these risks while providing the aesthetic and shade benefits.

Tree Hazards

Trees pose major concerns as an ember source in neighborhoods. Pines, in particular, have cones that can ignite or be carried a great distance by wind. Another common problem is from leaf or needle drop onto roofs where they become dry tinder during the fire season. Trees with limbs that are near or above power lines also have potential to spark and ignite.

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Trees that are positioned too closely to a house are especially hazardous as they can ignite and apply heat towards the side of a structure, bypassing any other home hardening measures in place.

Proper Tree Landscaping

Trees should be planted so that the edge of the crown is at least 10 feet away from the nearest structure. This reduces the volume of litter drop on your roof, but also reduces the potential for falling branches to damage your roof and protects your foundation from root growth.

This is not always achievable, so use the information here to prioritize risks. Make short-term and long-term plans to gradually increase the distance of trees from your structure with pruning and replacement.

  1. Prune Branches: Branches that overhang the roof or power lines should be pruned immediately to eliminate or minimize the overhang. Power lines that cross your property are your responsibility and not that of the power company. A licensed arborist can be consulted to remove such branches and any others that may grow into a hazard.
  2. Disconnect Tree Crowns: During hot, dry wildfire events, flames can easily jump from tree to tree. Make sure the tops of your trees are not touching to help slow the spread of fire.
  3. Remove Non-Native Species: Italian Cypress, Eucalyptus and Palm trees are especially prone to ignition and burn very quickly. These species are known to produce large quantities of embers, which increases the probability of your structure igniting.
  4. Replant on Southern Edge: Planting trees on the southerly side of buildings is a good energy saving practice. Trees in this location shade the building in the summer and permit passive solar heating in the winter. Deciduous trees lose their leaves for part of the year, which helps to reduce their flammability hazard (although it is still an indirect hazard because of leaves that are dropped).
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