California Oaks and Fire: A Review and Case Study

California has a fire-prone Mediterranean climate, and many of its nine species of native oak trees are thought to have evolved with fire. Little has been widely published about the role of fire in the oak recruitment and mortality in the western United States, and there has been some debate about how to reintroduce fire into oak woodlands. We present here a review, synthesis, and analysis of the literature on fire and California oak species. This literature review suggests high overall survival of oaks after fire, although smaller individuals often experience topkill (death of all above-ground stems, followed by recovery via sprouting of basal shoots from the root crown). We then provide results from a case study of a controlled burn on the survival of 5-year-old valley oaks (Quercus lobata) at a restoration research site near Davis, CA. Onehalf of the trees at our site were exposed to a set of prescribed burns in summer 2003, and another half were left unburned as a control. Prior to burning, measurements were taken on each tree’s height, diameter, and understory grass biomass. Fire temperatures were measured using temperature-sensitive paints on ceramic tiles hung on each tree. Only 3 percent of the oaks died as a result of the fire, although 85 percent were topkilled. Smaller trees, trees exposed to higher fire temperatures, and trees with higher levels of understory biomass suffered more damage. About one-third of trees over 200 cm tall escaped being topkilled. Our investigation of the effects of fire on young valley oak trees indicates that saplings of this species, similar to the saplings of most western oak species, are resilient to fire, especially if managers are willing to accept the temporary setbacks associated with topkill.