California oak savannas are dominated by blue oak (Quercus douglasii), valley oak (Q. lobata), interior live oak (Q. wislizenii), coast live oak (Q. agrifolia), and Engelmann oak (Q. engelmannii), occurring in mixed or monospecific stands occupying less than 30% cover. Nine tree species of oaks occur in the state (Pavlik et al. 1991), but four are limited to forests or woodlands. Annual grassland is the major understory type, although some savannas may have a shrub understory component. Nomenclature follows Hickman (1993).
The oak savannas of California generally occur at elevations ranging from 60 to 700 m between annual grasslands at lower elevations and mixed conifer or ponderosa pine (Pinus ponderosa) forests at the higher margin. Precipitation occurs primarily during winter to early spring, generally late October through April. Thus, oak savannas persist through a severe, annual drought period lasting 2–11 months.
Ninety percent of the oak savannas in California are privately owned (Ewing et al. 1988). Over 300 species of vertebrates live in oak savannas and woodlands of California (Jensen, Tom and Harte 1990). Livestock are the primary users and the primary economic products of the savannas; firewood, wildlife, and water are secondary products (McClaran and Bartolome 1985; Standiford and Tinnin 1996).
Past and Present Geographic Distribution
Oak distributions have been in flux throughout the geologic record because of changes in climatic patterns, which led to migration and juxtaposition of communities, with each individual savanna species responding according to its own tolerances (Evett 1994).