A gallery of oak trees and information specific to their respective species.
One of the most proven, if inconsistent, of the non-native oaks utilized in California over the last century and a half is the famous Cork Oak (Quercus suber). Here we see it growing under unusual conditions, in Santa Cruz, as a pair of rather old street trees. These trees have been pruned for the power lines above for many years, well beyond the 20 years that these trees have been directly observed. The soils in this part of Santa Cruz are quite good, and support some of the largest trees in town. Cork Oak is evolved for just this type of Mediterranean soil condition, and these trees appear to be deeply rooted, given the size of the trunks and the small sidewalk openings. Of special note is the "elephant's foot" aspect of the trunk on the right, as the trunk grows out over the curb, rather than lifting it. This type of trunk behavior has been seen elsewhere in coastal California, particularly with London Plane Trees (Platanus x hispanica).
Cork Oaks (Quercus suber) can be found growing and thriving throughout Santa Cruz, and here we see a well-structured tree growing in San Lorenzo Park, near downtown. There are numerous Cork Oaks in the park, in several groves. Through much of their lives, the trees have been growing in turf, a condition not typically recommended for Cork Oak, as a variety of trunk and root diseases can occur. In this case, the survivability is likely linked to the fact that the park is essentially on the banks of the San Lorenzo river, with very fast-draining alluvial soils. With a small amount of detective work, Cork Oaks can be found throughout California, with arguably the largest growing in the fantastic soils of Davis, where examples have reached 5 feet or more in trunk girth. In recent decades, Cork Oak has been hamstrung in the California landscape due to its susceptibility to root disease when grown with girdled and circling roots, which, sadly, have been the rule of the California nursery industry for 50 years or more. The growth habit of Cork Oak also varies enormously, very much like California native Valley Oak, with growth habits ranging from very upright, to highly penduous. As with any tree, pendulous types have limited utility in typical urban installations, due to the high levels of maintenance associated with maintaining clearances for pendulous species. Pendulous trees are also slow to put on height, which is a key goal of urban tree plantings.