California oak woodland is a plant community found throughout the California chaparral and woodlands ecoregion of California in the United States and northwestern Baja California in Mexico. Oak woodland is widespread at lower elevations in: coastal California; interior valleys of the Coast Ranges, Transverse Ranges and Peninsular Ranges; and in a ring around the California Central Valley grasslands. The dominant trees are oaks, interspersed with other broadleaf and coniferous trees, with an understory of grasses, herbs, geophytes, and California native plants.
Oak savannas occur where the oaks are more widely spaced due a combination of lack of available moisture, and low-intensity frequent fires.
The Oak woodlands of Southern California and coastal Northern California are dominated by Coast Live Oak but also include Valley Oak California Black Oak Canyon live oak and other California oaks. The foothill oak woodlands around the Central Valley are dominated by Blue Oak and Gray Pine (Pinus sabiniana).
Blue oak woodlands cover about 2,939,000 acres (11,890 km2) of the state, and of this area about 79%, or 2,322,000 acres (9,400 km2), shows no evidence of past cutting of trees. Recent research by the University of Arkansas Tree-Ring Laboratory has studied several unlogged stands of Blue Oak woodlands, and suggests that the state may harbor over 500,000 acres (2,000 km2) of such old growth forests. This would make California's oak woodlands some of the most extensive old growth forests left in the state. However, most oaks of full tree size are more than one hundred years old, and few saplings are ever produced, because cattle often tear the plants to pieces.
The Oaks 2040 survey estimates that 750,000 acres (3,000 km2) of California oak woodlands are seriously threatened by 2040 as a burgeoning state population makes ever more use of the wildland. This comprehensive survey includes oak woodland maps and inventory data for the ten oak types found in California. By evaluating this new information against current State of California economic growth projections, the location and extent of oak woodlands most at risk of development are identified.