Valley Oak Woodland Valley Oak Woodland by Lyman V. Ritter Vegetation Structure. Denser stands typically grow in valley soils along natural drainages.
Tree density decreases with the transition from lowlands to the less fertile soils of drier uplands.
Similarly, the shrub layer is best developed along natural drainages, becoming insignificant in the uplands with more open stands of oaks. Ground cover consists of a well-developed carpet of annual grasses and forbs. Tree associates in the Central Valley include California sycamore, Hinds black walnut, interior live oak, boxelder, and blue oak. The shrub understory consists of poison-oak, blue elder, California wild grape, toyon, California coffeeberry, and California blackberry. Various sorts of wild oats, brome, barley, ryegrass, and needlegrass dominate the ground cover.