Quercus Lobata - Description and Ecology

Description and Ecology

The sturdy trunk of the Valley oak may exceed two to three meters in diameter and its stature may surpass 30 meters in height. The "Henley Oak", in Covelo, California, is the tallest known North American hardwood, at 151 feet (46 m).

The branches have an irregular, spreading and arching appearance that produce a profound leafless silhouette in the clear winter sky. During Autumn leaves turn a yellow to light orange color but become brown during mid to late fall. In advancing age the branches assume a droopin characteristic. Its pewter-colored rippled bark adds to the attractive aesthetic of this species.

Typically, leaves are five to ten centimeters in length and are roundly and deeply lobed. The leaf width is approximately one half its length. Each leaf is matte green with an underneath pale green appearance; moreover, the leaf is covered with abundant soft fuzz, yielding an almost velvety feeling. When a fresh leaf is rubbed or broken, an aromatic scent is exuded, evoking a forest odor. The wood is a dull brown approaching yellow, and it has not been used extensively for milling.

Over most of the range, acorns fall in October. A variety of mammals and birds eat them, including the Acorn Woodpecker, Western Scrub Jay, Yellow-billed Magpie, and California ground squirrel. The acorns are also attacked by bruchid beetles, but can survive moderate levels of infestation. Surviving acorns all germinate in their first winter, and none remain by mid-winter. The acorns are medium to dark brown and range from two to three centimeters in length. The caps have deep stippling and are found most often as singlets, but occasionally as doublets. The Concow tribe call the acorns lō-ē’ (Konkow language).

Globular galls up to several cm. in diameter are frequently attached to twigs of mature specimens of Valley Oak. These house the larval stage of small indigenous wasps Andricus californicus. A related wasp species, A. kingi, produces small galls shaped like Hershey's kisses on leaf surfaces. The valley oak is the only known food plant of Chionodes petalumensis caterpillars.

Like many oaks, Valley Oaks can tolerate wild fires. Although smaller individuals may be top-killed, most resprout from the root crown