Valley Oak Woodlands
Valley oak woodlands are typically common on floodplains higher and farther from the main channel than other riparian plant communities. Mature valley oaks (Quercus lobata) dominate this plant community. The oaks are typically widely spaced, though often the trees form denser stands which create a closed canopy. The adult oaks range from medium to large - 15 to 35 m in height and are typically the only tree present. Below the open canopy of oaks, the grass and forb understory is often dominated by creeping rye grass (Leymus triticoides) and frequently by non-native invasive grasses. Interspersed among the oaks may be blue elderberry (Sambucus mexicana), box elder (Acer negundo), western sycamore (Platanus racemosa), Oregon ash (Fraxinus latifolia), Fremont cottonwood (Populus fremontii), and lianas of poison oak (Toxicodendron diversilobum) and wild grape (Vitis californica). Parasitic mistletoe (Phoradendron spp) can be found growing on the oaks.
Structurally, Valley oak woodlands have a medium-tall open overstory of oaks, with a moderately dense to dense understory of shrubs and occasional openings where grasses and forbs are dominant. Such structure provides higher perching and nesting sites, low cover and nesting sites, and a source of invertebrates common in grasses and forbs. The seeds and fruits of blue elderberry, poison oak, wild grape, mistletoe, all provide food sources, along with abundant acorns from the valley oaks. Valley oak woodlands are important to many wildlife species because of the foraging, cover and nesting habitat they provide. For example, more resident breeding birds in the Central Valley use Valley oak woodlands than any other plant community type.
For more information about Riparian Plant Communities see Conard and others 1977, Gaines 1980, Holstein 1984, Holland 1986, and CWHR 1988.