Recently, a Los Angeles Times article suggested planting coast live oaks (Quercus agrifolia) as fire-resistant trees for landscaping after the Southern California wildfires. The first thing that popped in my head while reading this was “How is an oak tree fire-resistant? Is this really true?” I had to check it out.
Coast live oaks are a native tree typically found along the coast from Mendocino County to northern Baja, Mexico and inland about 50 miles. While they are more prevalent in Southern California, they can be found in Solano County and in the Delta. The hallmarks of this evergreen tree include thick bark and an ability to sprout. The evergreen leaves can conserve energy for recovery from fire, because the tree doesn't have to replace all of its leaves each year. In addition, the tree bark of a mature tree is the thickest of all native oaks. The tree bark has a thinner outer layer that is “dead” and a thicker inner bark layer that is living. A young tree will have smooth gray bark that will gradually mature to a brownish color with slight furrows.
The roots are wide-spreading, providing food storage for the tree and are covered with a corky layer as well as the soil that protects them from fire. When the tree appears to be destroyed by fire, the root crown sends up sprouts with the energy provided by the roots' food storage reserve. This usually occurs in about 2 months from the fire but can take 2-3 years. Trees that have lost part of their crown usually regain the coverage in 8-10 years after the fire. Gnarly, twisted limbs and multiple trunks are often the result of sprouting after fires, and limbs can sprout horizontally as well as vertically. Trees like this are sometimes described as having a haunted appearance.
Smaller diameter coast live oak saplings usually recover quickly from even a moderate intensity fire. Basal sprouting usually occurs. Large diameter trees (18 inches or more) survive better after the severe fires especially if the understory had been cleared before the fire. Post-fire, trees with cambium burns/wounds to the trunk that are only a few inches can recover, but larger injuries make the tree susceptible to insects, bacteria and fungi.
Coast live oaks are also susceptible to Sudden Oak Death with the large, healthy mature trees dying from a few weeks to just a few short years. Research has shown that coast live oak is a fire-resistant tree with the potential for recovery after even a severe fire. It is the only oak tree that seems to have this capability, but its Achilles heel is Sudden Oak Death. It will be a difficult decision for homeowners who are rebuilding and re-landscaping after the fires whether or not to plant/replant this beautiful tree.
Pavlik, B.M., Muick, P.C., Johnson, S.G., Popper, M. 2020. Oaks of California. Cachuma Press and the California Oak Foundation
Steinberg, Peter D. 2002. Quercus agrifolia. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: https://www.fs.usda.gov /database/feis/plants/tree/queagr/all.html [2025, February 4].
Calflora, a 501c3 non-profit, Quercus agrifolia website