There aren’t many native live oaks on our streets, though we can see them easily enough up in Tilden Regional Park, in private yards, and in some public places like the UC Berkeley campus. The ones on campus are survivors (so far) of an unfortunate rash of deaths caused not by Sudden Oak Death Syndrome but by landscape errors.
Our live oaks are very well adapted to the natural climate here. They have small, tight, hard, glossy leaves that don’t transpire a lot of water, so they make it through the long dry season quite nicely. But they’re susceptible to certain root fungi that thrive when they have both warmth and moisture—in other words, with summer irrigation. Watering lawns is the most notorious form of summer irrigation in cities and suburbs, and a nice lawn to relax on in the shade of a mighty live oak seems to be one of those campus idylls. Unfortunately, it can be fatal to the mighty tree in question; also unfortunately, oaks typically die slowly, over a decade or so, and cause and effect aren’t always obvious.
If you are lucky enough to have a live oak on your property—probably a coast live oak; that’s what we see the most of on this side of the hills in yards as well as in the wild—you’d be well advised to take care what’s planted under it, so you don’t have to irrigate. Plant now to give your understory the winter rains for breakfast; you can find a list of drought, and shade-tolerant plants, many of them native, at any good nursery or in Marjorie Schmidt’s classic Growing California Native Plants.
Our live oaks, especially coast live oaks, are under well-publicized threat lately from Sudden Oak Death Syndrome, caused by a phytophthora, which is an odd organism indeed—not a fungus, exactly, though it gets called “water mold.” It’s being tracked through a number of other hosts, including garden-variety (unfortunately) rhododendrons and our own wild tanoaks, who seem to be falling to it at a faster rate than true oaks. What effect the disease might have on wildlands is still unknown; it’s possible that individual trees that die of it are just more susceptible than their brethren, and that there’s enough of a resistant population to keep the species going just fine.
If SOD does prove devastating to live oaks, it will devastate more than them. Oaks in general, and live oaks where they’re plentiful, are “keystone species” here. Upon them depend an incredible number of other species, from charismatic megafauna like deer (who eat acorns) and the predators who eat deer, to smaller animals like tree and ground squirrels, packrats, chipmunks, and arboreal salamanders; innumerable birds: scrub and Steller’s jays, acorn woodpeckers, and others eat acorns, and other species (like sapsuckers) eat sap or (like black-headed grosbeaks) eat spring’s catkin flowers.
Oaks host other species such as a dizzying array of gall wasps, and parasite mistletoe, which in turn feed ichneumon wasps and other insects, phainopeplas and waxwings. Oak moths can strip a tree—but it usually recovers—and in turn support whatever birds are around and feeding hungry youngsters. And many species nest in, shelter in, hide under, or hunt from oaks. I suppose a commune of acorn woodpeckers in the Berkeley flats is too much to hope for, but I know that the live oaks near my house are supporting wildlife, because I have many optimistic oak sprouts from buried acorns every year. I generally leave them to grow, just to see what happens. If any turns into a tree, I’ll change my garden plan accordingly.
A staggered file of young live oaks graces the center of University Avenue along with ceanothus and alternating strips of grass lawn and drought-loving groundcover and flowers. There are more in the median lawn of Sacramento Street south of University, along with several other nice species like California buckeye. I notice that there are Crataegus specimens there, too, and senior ash trees along the sidewalks. Some wit has seen to it that the street has oak, ash, and thorn together, and may they all bless the neighbors and the rest of us too.