leather oak (Trees & Shrubs of the Sunol Region

leather oak

Quercus durata

Summary ⁷

Quercus durata (California Scrub Oak, Leather Oak; syn. Quercus dumosa revoluta Sarg.) is an oak endemic to California.

Distribution and soil substrate ⁸

Q. durata is highly tolerant of ultramafic soils, those that are high in magnesium and low in calcium concentration, and also characteristically high in nickel and chromium content. These soils are often reddish soils are typically nutrient poor.

Roger Raiche has correctly pointed out that the botanical literature on Q. durata overstates the species reliance on ultramafic substrates, when, in fact, this oak is found on a variety of volcanic and other non-serpentine soils within the California Floristic Province.

Q durata is the dominant shrub in Sargent Cypress (Hesperocyparis sargentii) woodlands, which occur in coastal portions of the California Counties of Mendocino, Sonoma, San Mateo, Santa Clara, Monterey, San Benito, San Luis Obispo and Santa Barbara as well as portions of the San Francisco Bay region. The Cedars in Sonoma County is an example of a Sargent Cypress coastal site. In more protected inland locales this woodland type may extend into a riparian zone where summer fogs persist. Grey Pine (Pinus sabiniana) may occur with Sargent Cypress in northern California, while Coulter Pine (P. coulteri) is a common associate in central and southern California. Cypress (Hesperocyparismacnabiana) woodlands are a somewhat less common ultramafic plant association where the Leather Oak may be a dominant shrub.

Ultramafic chaparral is another common plant community that is found below elevation 500 meters from Santa Barbara County north through the North Coast Ranges and also within the foothils of the Sierra Nevada and portions of the California Central Valley. Here co-dominant shrubs are Chamise (Adenostoma fasciculatum), Coffeeberry (Frangula californica), Interior Silktassel (Garrya congdonii). Buckthorn (Rhamnus crocea) and Toyon (Heteromeles arbutifolia). Scattered taller occurrences of California Bay Laurel (Umbellularia californica), Canyon Live Oak (Quercus chrysolepis) and Coast Live Oak (Q agrifolia) are also found here.

Q durata is found outside of serpentine environments such as within the Vaca Mountains of Solano and Napa Counties or Hale Ridge of Lake County. In these cases Leather oaks typically occur as isolated individuals within a backdrop of plant associations dominated by California Scrub Oak (Quercus berberidifolia) and Interior Live Oak (Q. wislizeni).