Have you ever reflected on the natural habitat preferences of humans? There are so many factors that contribute to where we actually live – economic opportunities, market availability, infrastructural access, social ties, and a host of other more proximate determinants – that it is easy to forget the possibility that people might have an innate biological preference exerting a more subtle influence on our favored choice of abode. Questions of the appeal of suburbia’s relative spaciousness versus the different enticements of urban living are inextricable from cultural and political preferences. So let’s set all that aside as much as possible and consider a simpler and more isolated claim:
Whenever he can, the Californian prefers to make his home beneath an old Live Oak’s shade.
– Donald Culross Peattie, A Natural History of Western Trees, 1950
Peattie, an old-fashioned naturalist, stated this inclination of the Californian subspecies of human much as he might describe that of many another creature. Badgers burrow. Rails skulk in marshes. Tanagers cease their migration when they reach the forest. And Californians find themselves halting and thinking this is home when they step into the thick shade of a live oak. So says Peattie. Can I deny it? I was born in such a home, I live in such a home now, and to test at first hand the plausibility of this hypothesis I am sitting in such shade right now as I type this.
In my tree essays so far, I’ve rather tiptoed around the outskirts of our dendrological life, picking off the minor and adjunct species. But no more: coast live oak is the heart of our woodlands. It is the most abundant oak and most characteristic tree of our region, found abundantly in every county of the Bay Area, in habitats dry or wet, hot or cool, and even here and there surviving urban development due to their picturesque value which even the most committed city-dwellers are reluctant to destroy. This is the oak that gives its name to “Oakland,” the principal native tree that still adorns the old landscaped parks of our cities or the campuses of Berkeley or Stanford, the tree that past generations recognized as superior to any imported ornamental as they laid out their plans for spaces where civilization and culture would exist in harmony with nature. This is not to say that none were lost – millions were cut down – but the coast live oak was the most likely of trees to be spared the ax and granted its place in our towns and neighborhoods.
Peattie’s claim appears – both by my personal instincts and by these sociological and historical evidences – to have a substantial element of truth. We are perhaps less accustomed to make such sweeping statements on human preferences today, and for many who have not recently considered the tree itself, such a blunt declaration of their preferences made by some dead old naturalist may feel rather presumptive on his part. Or on mine, for endorsing it. But endorse it I do – and the only fair test of the Californian’s attraction to live oaks is a fresh, sincere, and personal look at this essential tree.
Natural Context
I’d better start by identifying exactly what tree we’re talking about.
“Live” oak means evergreen, as opposed to our deciduous valley, black, and blue oaks. More technically, we have three tree-sized live oaks in the Bay Area: coast live oak, interior live oak, and canyon live oak. Interior live oak (Q. wislizenii) is much like coast live oak on the inland foothills on the other side of the Central Valley, but appears in the Bay Area usually as a shrubby, stunted tree whose local subspecies sometimes goes by the name “chaparral oak.” It is distinguished from coast live oaks by its generally less convex leaves and by the absence of the small white fuzzy patches which can often be found on the underside of a coast live oak leaf. Basically, across the Bay Area, the big, beautiful live oaks are not the interior species, but the coastal.
Canyon live oak (Q. chrysolepis) is a significant tree of the Bay Area’s wild places, but one which far fewer of our citizens will encounter on a daily basis, growing as their name suggests in steep canyons and other rocky places. Canyon live oak is unique among our oaks in having some leaves with entirely unlobed margins, though it is also famous for the variability of its leaves, with some of the low-hanging examples typically toothed and spiny (to discourage browsing by deer).
So the primary tree under discussion here is the coast live oak, Quercus agrifolia. In typical daily conversation and in the spirit of convivial familiarity, however, it is perfectly acceptable to refer to your neighborhood Q. agrifolia by the simpler monikers of “live oak” or even just “oak.” I enjoy taxonomic etymology far more than the average person, but I deplore the fussy tendency to vouvoyer every tree, bird, and flower.
As for this “live” business – why be evergreen rather than deciduous anyways? Evergreen trees produce more durable leaves that last for several years, rather than having to expend the energy to produce a new set each spring. The most obvious pattern away from being evergreen is seen as one travels northward or to higher elevations, where broadleaf trees are dominated by deciduous species or replaced by conifers. This is because winter leaves are more vulnerable to damage in cold or snowy conditions, produce less energy as sunlight declines latitudinally, and the water needed for overall functioning and leaf maintenance becomes frozen in the soil. This last reason – a form of water scarcity – is one of the most potent forces shaping leaf design “decisions” throughout many climates.
In our summer-dry climate, a number of species (buckeye, valley oak, blue oak) opt for deciduousness despite our mild winter temperatures – one of the main drivers for this adaptation likewise seems to be the lack of water that prevents them from using their leaves all the way through fall without fatal desiccation. In well-watered, shady streamside locations, even these deciduous trees like buckeyes will hold their leaves for significantly longer than in sunny and dry locations, and in many cases our two ubiquitous evergreen trees – coast live oaks and California bay laurels – come to dominate these habitats. What is interesting about the coast live oak is its versatility – in these locations with plentiful water, its possession of evergreen leaves gives it a distinct advantage over many deciduous species, but it is a tree that can also thrive in hot, dry situations. They accomplish this by multiple smaller micro-adaptations within the broader evergreen template, shrinking their leaf size, curving the edges under, and covering the whole with a thick waxy cuticle. All of these adaptations serve to reduce water loss and make year-round leaves a viable approach even in conditions of fairly intense water scarcity.
The point of all these reflections on the highly adaptable leaves of the coast live oak is to underscore the ubiquity of these trees and the variety of habitats in which they thrive. Live oaks might join with bays to make a close, dark canopy along a creek. They might wade their way into the manzanita and chamise of sunny chaparral edges. They might spread themselves liberally among near-enough every variety of mixed woodland we have, associating at some time or other with every one of our other oaks species, madrones, buckeyes, toyons, maples, alders, sycamores, willows, and every other local tree you care to name. And unlike our deciduous oaks, both the coast live and canyon live oaks will join in with redwoods and Douglas-Firs as shady forest trees.
The Threat: Sudden Oak Death
The biggest issue in California oak conservation today is the spread of Sudden Oak Death, a virulent oak disease caused by a fungal pathogen scientifically known as Phytophthora ramorum. Originally of Asian origin, this pathogen was introduced into our state via nursery plants imported from Europe. It has since spread widely throughout the forests and woodlands of coastal California, most easily transmitted in water dripping from the foliage of neighboring trees. Some species are highly vulnerable and are quickly defoliated and die – coast live oak and tanoak are the worst afflicted. Many other plants – most notably California bay laurel – can host and transmit the fungus without themselves being killed.
Tanoak is in the most trouble. This member of the same beech family is not a true oak, bearing “acorn-like” fruits with tufted caps, but having distinctly un-oak-like flowers of erect, rather than hanging, catkins. Their vulnerability stems from their genetic susceptibility for both transmitting and dying from the disease and from their habitat preference, found in more or less constant proximity to bay trees, the most abundant vector for Sudden Oak Death. Tanoaks are expected to die out from the great majority of their range, although there has been a small amount of good news from the search for naturally resistant specimens. Here in relatively dry and forest-light Novato, we don’t have tanoaks, but elsewhere in Marin County, whether on Inverness Ridge on Point Reyes or around Mount Tamalpais, most visits to tanoak forests are now sadly abundant in dead and dying trees.
When found in these moister forest habitats with lots of bays, coast live oaks are similarly at risk. Due to their greater adaptability to dry and sunny habitats where Sudden Oak Death does not flourish, they are at no risk of extinction. But many forests until recently rich in live oaks will undoubtedly change over the upcoming years, with more resistant species like bays, madrones, or Douglas-firs taking their place. With the passing away of live oaks, opportunities for the animals that depend on them will decline and the forests will be diminished. We will still go the woods, still listen to the songs that continue, but with that melancholy sense of loss that Frost heard in the mid-summer song of the ovenbird:
He says the highway dust is over all.
The bird would cease and be as other birds
But that he knows in singing not to sing.
The question that he frames in all but words
Is what to make of a diminished thing.
Or as Thoreau famously put it in Walden:
I take infinite pains to know the phenomena of the spring, for instance, thinking that I have here the entire poem, and then, to my chagrin, I hear that it is but an imperfect copy that I possess and have read, that my ancestors have torn out many of the first leaves and grandest passages and mutilated it in many places. I should not like to think that some demigod had come before me and picked out some of the best of the stars. I wish to know an entire heaven and an entire earth.
The world is changing. While the slow decline of many species can happen at a pace nearly imperceptible to casual observers, the passing away of wide swathes of coast live oaks can happen much more suddenly, with the loss more stark and unavoidable. A patch of trees, still standing but with the evergreen leaves suddenly all dead and dry, is in its way as unsettling as a clear-cut or a forest fire: there is no tell-tale smoke, there are no saw and ax to blame, there was only a small mistake made hundreds of miles away, which crept into our own backyards and laid waste to our trees in the night. This is happening now, and our ability to prevent it is highly limited. Do not take the oaks for granted; they are far less permanent than the stars.
For more information on Sudden Oak Death and the scientific and citizen-powered efforts to understand its spread and possible avenues for control, prevention, or recovery, visit suddenoakdeath.org.
Creatures
But they aren’t dead yet! Life goes on, and the coast live oak has a well-established strategy of continuance that has seen it through many ages of the world. These live oaks, as with a great many members of the genus, depend on jays to distribute their acorns, heavy seeds that are not otherwise inclined to travel and which contain a rich nutrient load that is irresistibly enticing to a wide variety of creatures when not buried a few inches underground by the crafty jay. This is the most essential interspecies relationship in the world of oaks and I discussed it more in my valley oak essay. I also discussed the sculpture of Polykleitos and the films of Hayao Miyazaki, so you don’t want to miss that one.
Then there are a host of other creatures that like acorns – titmice, chickadees, nuthatches, and woodpeckers are all intimate associates with live oaks, feeding on acorns in fall and on the multitudinous other plant and insect life to be found among the oaks at other seasons. Most lack either the size or intelligence to cache whole acorns as they jay does; the major exception and a really very remarkable hoarder is the acorn woodpecker, who likes to stuff acorns into old, dead trees, or old dead utility poles, or nicely dead and suitably impressionable home siding.
Unfortunately for the oaks, none of these locations is really well suited for germination and the flourishing of seedlings. And acorn woodpecker hoarding doesn’t really exhibit a jay-level of intelligence, since they don’t have to remember thousands of different cache sites, and in fact they frequently exhibit obviously foolish variations on their strategy, such as dropping their acorns behind the siding of housings even when they fall down inside and are unreachable, or trying to stuff non-durable foodstuffs like a dead mouse into an acorn hole (I saw this once – it didn’t work). The other obvious eater of acorns is the western gray squirrel, who will save a stash for later, but tends to do so in a concentrated larder near the tree of origin, rather than planting them individually within a wide radius as the jays do.
They’re less cute than chickadees, less goofy than acorn woodpeckers, and less fuzzy-tailed than squirrels, but the plain truth is that jays are the greatest allies of the oaks. You might not like their brash, bullying behavior, but if you like oaks, you have to accept them!
Speaking of unpopular creatures who live among the live oaks: oak moths. There comes a time in April or so when the live oak woods can be rather dripping with their small caterpillars, dangling on long threads that sway in the wind until they deliver their burden to some useful place – or into your hair. As with many other relationships in nature, oak moths have a cycle of varying abundance: some years there will be many, other years there will be few. In extreme years, the caterpillars can nearly defoliate wide swathes of forest. Although rather alarming to encounter, this is not in the usual run of things fatal and is part of the normal long term pattern under which individual live oaks have lived for hundreds of years. So you can in good conscience see the swarm of caterpillars without being overwhelmed by regret, and instead enjoy the spectacle of the massive feast for the chickadees and bushtits and spring warblers and so on. For more on the California oak moth, Phryganidia californica, including pictures of all lifecycle stages – eggs, caterpillar, pupa, and adult moth – see this blog post from Bug Eric.
Flowers
Lots of things eat acorns. A few creatures, like the oak moths, eat even the mature leaves, spiny and tannin-laden though they are. And some birds and insects do also eat the flowers and fresh new leaf growth. But being small, not nectar-bearing, not odorous, rather greenish, and emerging early in the season, live oak flowers are easily overlooked. In the big picture, the general evolutionary trend of flowering plants has been towards animal pollination – using bright colors, enticing odors, and edible nectars and pollen to entice insects (and some other winged creatures) to travel from flower to flower, thereby providing a targeted and efficient fertilization service.
Oaks buck this trend. Instead, they have reverted to the old school method of the conifers: wind pollination. Long dangling catkins of tiny male flowers wave in the wind and send out many millions of pollen grains into the world, where a few of them will hopefully find themselves wafted directly into the tiny, sticky target of the inconspicuous female flowers of other trees, tucked into the axil buds and essentially invisible to casual human eyes. This strategy is relatively desirable when you are a large tree (height helps in spreading pollen by wind), when you flower early in the year (when comparatively fewer pollinating insects are available), and when you are long-lived (so a rain-drenched or uncooperatively winded failure of a year doesn’t ruin your long-term reproductive prospects). All apply to oaks, and by the general success of the genus you can tell that this is still a perfectly valid strategy.
There is one more feature of oaks and their wind-pollinated lifestyle that bears emphasis: “oaks,” in the words of Bay Area tree expert Glenn Keator, “are notoriously promiscuous,” accepting pollen from a range of species beyond their own. This is part of the puzzle of oak identification: in addition to being highly variable depending on local environmental conditions, many species will also hybridize regularly. We have two major oak lineages: the white oaks with rounded lobes (valley oak, blue oak, Oregon white oak), and the black oaks with pointy lobes or spiny tips (coast live oak, interior live oak, black oak). Within each of these two lineages, hybridization is not only possible, but indeed frequent and to be expected in areas of overlap between species. A simple and direct example is the so-called “oracle oak,” representing a hybrid between interior live and black oak. In some specimens, however, it is not so much a simple case of parents of two different species, but one of a longer line of mixed heredity in varying proportions.
Closing Words
So there are your ecology lessons for the day. Oak flowers are inconspicuous but promiscuous wind-pollinators. Oak fruits (acorns) on the other hand are much too big for wind dispersal, and require the allure of deliciousness to enlist the help of animal assistance, most notable that of jays. Coast live oak leaves are durable and water-retentive and evergreen, but can be eaten by the voracious caterpillars of the California oak moth. These tough leaves are adaptable both to hot, dry locations and to cool, shady spots – but the latter habitat is now being heavily impacted by the introduced Sudden Oak Death pathogen, which spreads through moisture and various host plants, most notably bays.
The goal of all this information is simple: to help you to understand what you see when you notice where a live oak is growing, how it’s going about the business of reproducing, how it’s interacting with the animals that rely on it, or how it may one day die, suddenly and with little warning. All of this is valuable, gives context, and deepens sympathy. But even with little of this knowledge, even with none of this knowledge, I still adhere to Peattie’s declaration that this is the tree that Californians are drawn to. The initial visual appeal of the coast live oak which captures our attention and elicits our interest can be described, but is not replicated or replaced by facts and words like those here. Peattie crafted such a description as well as anyone could, but ultimately you must look at the tree for yourself. Do so now, for today even the live oak leaves are falling faster.
Dramatic, romantic, pictorial and picturesque (to choose but a few possible adjectives), the Coast Live Oak certainly is. For it seldom grows tall and straight; almost inevitably its trunks lean this way or that, its long sinuous branches twist and turn, and eventually with a down-sweeping gesture will come, in old trees, to reach the ground. So that every Coast Live Oak is an extreme individualist, utterly unlike every other in the world, and yet the sum and total of all its many variations adds up to a composite picture of ample grace, of grace combined with strength, that make it recognizable at a glance as distinct from any other tree within its natural range.
– Donald Culross Peattie, A Natural History of Western Trees
Header photo: Coast live oak acorns by Eric Hunt.
Compelling, sad, remarkable & lovely. Thanks, Jack!
Wow, what an article! So informative and lovely to read. Thank you!
“Do so now, for today even the live oak leaves are falling faster.”
Yes, now is the time for appreciation and care for our natural world.
Wonderfully written.
Thank you Jack!