So distinctive are California’s grassy hills and oak-studded valleys, that I wondered what changes have taken place to the very look of the landscape. Restoration can help move these habitats back to diversity and health, but what if the structure and pattern of the trees on the land is a result of factors that occurred centuries ago, and we do not even realize this? For restoration to be successful these past causes and effects must be understood, and historical ecology can give clues towards working with woodlands and savannas.
How have oaks evolved under ecological processes that may have been altered since the arrival of European settlers to the state? Changing fire regimes, new grazing animals, climate change, irrupting diseases -- there are many processes to study when trying to get the feel of the old oak communities. But “old” is a key word here. For beings that live centuries, long past the lifespan of a scientist or observer, how do we begin to unravel the tangle of clues present in our own snapshot of time? We try to comprehend the situation of a minute fraction of the lifespan of these tree giants, but their lives go on beyond our generations and we often miss their births, reproductive years, and deaths. But as we shall see botanical “detectives” have begun to piece together a story from the slice of evidence we can find today.
A Lifespan Older Than Humans
So distinctive are California’s hills and valleys with oak, that I wondered what changes have taken place to the very look of the landscape. How have oaks evolved under ecological processes that may have been altered since the arrival of European settlers to the state? Changing fire regimes, new grazing animals, climate change, irrupting diseases -- there are many processes to study when trying to get the feel of the old oak woodlands and savannas that are so characteristic of our state. But “old” is a key word here. For beings that live centuries, long past the lifespan of a scientist or observer, how do we begin to unravel the tangle of clues present in our own snapshot of time? We try to measure the growth of a few days-worth of “fingernail” on these tree giants, but their lives go on beyond our generations and we often miss their births, reproductive years, and deaths. But as we shall see botanical “detectives” have begun to piece together a story from the evidence we can find today.
Before I owned a car, I took a backpack and bicycled along the inland Bay Area routes through oak hills and valleys searching for plentiful acorns trees in October. Many California tribal people said the Coast live oak made a good staple acorn to gather due to its abundance and flavor; acorns of Blue and Valley oaks were said to be inferior in taste; but the gem of the acorns was the California black oak, told to be of the highest quality in taste. I searched out the nearest black oak grove, but learned that this oak produces a crop only every two years. The trees were barren. So I turned to Coast live oaks and soon found a grove that had a huge crop -- acorns were dripping off the branches and littering the ground. Collecting bagfulls, I took them home and cracked them open with a rock while sitting out on the patio at home, arranging the yellowish nut-meats to dry hard in the sun.
I sorted the wormy ones from the good, and soon a pair of Scrub jays noticed my refuse pile. One flew done near me, hastily grabbed an acorn in its bill and flew off. The second jay then did the same, and I watched amused as the whole pile disappeared. The jays stored them for later use, hiding them in the ground, hammering them deep and sometimes placing a leaf over the spot, perhaps to make sure a marauding squirrel would not steal them. The jays worked to place other acorns into crevices of tree trunks, the gutter of my house, and into potted plants. A particularly greedy jay stuffed two to three acorns at a time into its bill at each visit to the pile. The jays had an excellent memory for these varied caches, and I watched them eat an occasional acorn through the winter from these stores. Some, however, were missed. (Nineteen years later I saw five sapling oak trees in my yard, sprouted from a few forgotten acorns planted by jays.)
A curator at a local museum let me borrow an Indian stone mortar and pestle from a dusty basement shelf. This wondrously elegant acorn grinder was slightly larger than a bowling ball with a deep cup polished from use. The accompanying pestle was made from rougher basalt, giving a tooth for breaking up the acorns.
I sat outside with reverence for this old tool, pausing and wondering about the hands that made it, the history that it had seen. Pouring acorns into it, I began to pound with the pestle. The rhythmic hollow thuds must have been a pleasing sound in California oak groves for thousands of years. The Scrub jays sat in a tree and watched me. To my delight the process went much faster than when using a coffee grinder. The efficiency of old tools can sometimes not be improved upon, I thought. I was able to pound piles of acorns into powder, and soon had enough for many meals.
To make the bitter meal edible, its tannic acid had to be leached out with many soakings of fresh water, once done by the creeks in shallow sand hollows where water could be passed over the meal that was spread out. Ground finely enough, it would stick together like jello and could be picked up in chunks by hand. My method involved laying a bed of pine needles out in my backyard and placing cheesecloth over this. I spread the meal out on the cloth and poured cold water over the bed, allowing the water to soak through. This phase took several hours.
The resulting acorn mush had a subtle flavor, oily and slightly nutty. Next I wrapped cakes of mush in the leaves of sword fern, but unable to bury these in hot coals in a ground pit to bake as was traditional, I covered them in aluminum foil and baked them in my oven slowly into bread, a bread unlike any made from wheat flour. The bread cakes were dark brown and crunchy, delicious with a hint of tannic flavor like spent tea leaves.
I now had more respect for the work of making acorns into food for humans, however imperfect my experiments had been. And I gained a deeper understanding of the acorn itself, abundant, flavorful, seasonal, locked with secrets. Through the early and middle Holocene native people apparently relied upon grinding grass and wildflower seeds using flat millingstones and handstone cobbles (also known as metates and manos in Spanish) as a mainstay of food. From archaeological evidence, a major switch to acorn-grinding using rounded mortars and pounding pestles happened about 4,000 BP in San Francisco Bay, by 2,800 BP in the Central Valley, and at 1,000 BP in the Sierra Nevada (Basgall 2004). The oiliness of the acorns inhibited efficiency of the sliding action of metates and manos -- pounding in a mortar worked much better.
The Scrub jays hopped over to my refuse pile and bravely snatched acorns up in their bills, sometimes greedily stuffing in two or three. They flew off to different parts of the yard, pushing them into the dirt and neatly placing leaf litter over them, or inserting the nuts in a tree trunk crevice. Ten years later several planted in soil by the jays grew into sapling trees -- an oak woodland in the making. Twenty years later a woodland was forming. At Hastings Reservation in Monterey County Scrub jays each cached about 5,000 acorns every fall. A full 95% were estimated to have been relocated by these blue-white birds and eaten. The other acorns often germinated (Carmen 1988, McBride et al. 1990). Stellar’s Jays and Yellow-billed magpies also cache acorns.
Other seed predators in the past were humans. But when the acorn crops failed, Native people often turned to the California buckeye (Aesculus californica), mashing its bitter fruit as a poor substitute for the oak’s bounty and letting the remainder of the stores sprout into trees. The buckeye’s distribution has been influenced by people for perhaps thousands of years -- it often grows in “orchards” at archaelogical sites and old Indian camps. Also associated with midden sites are California black walnut, as at Walnut Creek (Contra Costa County) and Round Valley (Mendocino County) (Gordon 1974).
Coast Live Oak
Live Oak Woodlands
Having lived most of my younger life next to deep Coast live oak woodlands I have a large store of memories hiking on trails through oaks, fascinated by the changes that happened to the woodland from season to season: in the dead of winter I walked on a trail during a light rain and heard the eerie calls of Varied thrushes hiding in the oaks -- long, thin organ-like notes -- and the tinkling calls of spritely Golden-crowned kinglets. Early in the spring the Trilliums and Milkmaids (Dentaria californica) bloomed on the woodland floor, and pink currant bushes burst into flower, attracting February Allen’s hummingbird migrants. Later, the oaks burst full of the songs of Wilson’s and Orange-crowned warblers, dogwoods showed large white flowers, and the oaks themselves produced small strings of wind-pollinated flowers. By June I looked forward to picking thimbleberry fruits. September, October, and November marked the season of acorns.
Then, having walked these trails for longer periods, over 10 or 20 years, I noticed longer natural cycles that happened only once or twice a decade. An El Nino storm caused a landslide one day in the oak woodland, opening up the dense canopy and revealing a huge barren scoop of mud. I watched the pioneer plants gradually colonize this bare area, then sapling trees and shrubs grew, and after 10 years a new woodland developed. Another year, the California oakworms had a natural outbreak. This moth larva, Phryganidia californica, feeds on the leaves of the oak as a caterpillar that usually is unseen on leaf margins. But on rare years its population densities increase terrifically, and the oaks are almost completely defoliated by them. Walking the oak trails that summer was different than any other -- sunlight poured through the normally closed evergreen canopy, and masses of partly eaten leaves littered the woodland floor. Next year the worms virtually disappeared, and the oaks resprouted new leaves.
Some changes to the oak woodland were quick-lived and unexpected. One afternoon while waiting for an evening class in an open space park in the town of Pleasant Hill, I strolled through grassy openings of Coast live oak and Blue oak woodland, enjoying the slight fall colors of the deciduous Blue oak leaves turning yellow ocher and tan. I suddenly felt dizzy as I stood observing the scenery, and wondered if for some reason I was about to faint. But then the very earth beneath me began to roll and jolt, back and forth, the first heave nearly throwing me off my feet. An earthquake! I realized, and rode it out. This one seemed to go on for several seconds, shaking many leaves off the Blue oaks, and startling a pair of ducks off a nearby pond. To my amazement Mt. Diablo in the distance moved as well as if sitting in a giant rocking chair. I then noticed a Gray fox that had been completely hidden curled up in a ball in the oak leaf litter; it quietly stood up, looked around, and nestled back into its bed. The rolling stopped, and all was quiet. A few birds called, but I continued my hike as if all was normal. Not until I returned to my car and switched the radio on did I realize that this was “The Big One.” October 1989, and away from the peace of the oak woodland, sirens blared, traffic lights went out, and horrendous news came of parts of San Francisco burning. I marveled at how different my rather serene and curious experience of the earthquake among the oaks was compared to that of the urbanized world. The oaks seemed not to change much at all.
Lately I came to see some of the unusual changes to the live oak woodlands that were not naturally cyclic, but wrought by modern humans. While walking one day a few years ago to one of my favorite trails through the oaks, I was stopped by an orange warning fence blocking the trail. A sign prohibited entry due to Sudden Oak Death, a newly discovered disease that has been killing Coast live oaks in the San Francsico Bay Area and central coastal counties north to Oregon. Sudden Oak Death was first reported in 1995, and has been attributed to the fungus-like pathogen Phytophthora. These organisms apparently enter the bark of susceptible trees causing girdling of the bark and rapid death. Marin County was a hotspot for the tree kills, affecting Coast live oaks, California black oaks, and Tan oaks. Other species of Phytophthorahave been a serious problem for trees and agricultural crops in various parts of the world (Kelly 2001, CalPIF 2002). I avoided the trail, but fortunately other oak trails were still open.
Finally, I became aware of changes to the oak communities that have taken course over time periods longer than my life span, changes from factors that occurred a century or more ago: disappearance of oaks due to European settlement practices,introduced plant and animal species in oak habitats, and altered fire ecology of oak communities. The varied habitats of Coast live oaks have had many such changes.
Today Coast live oaks grow in two basic vegetation types: closed-canopy woodlands and open savannas. Oak woodlands occupy extensive areas along the lower slopes of deep canyons along the central Coast Ranges, and in drier areas break up into oak “parklands” consisting of a mosaic of small closed groves and open grasslands. Oak savannas are essentially a grassland/shrubland community with scattered lone trees.
Dense oak woodland, which is favored on north-facing canyon slopes of coastal hills has a highly diverse shrub and forb layer.
The “Southern Oak Woodland” of the central Coast Range south to Baja California often contains Toyon (Heteromeles arbutifolia), California coffeeberry (Rhamnus californica), California sagebrush (Artemisia californica), Black sage (Salvia mellifera), and Laurel sumac (Malosma laurina). From Santa Barbara to Orange County,California walnut (Juglans californica var. californica) joins the Coast live oak in open groves.
Historical evidence indicates that similar oak woodlands and parklands clothed California’s hills and valleys in the past.
Pedro Fages in his march up the coast of California in 1769 described what are probably these oak woodland communities. One league (approximately 2.64 miles) from San Gabriel Mission (around Pasadena) he declared “there are great forests of oak...” and many Indians lived there, aa well as deer among other wildlife. At San Luis Obispo he and his party found dense oak forests in the surrounding canyons -- these can still be seen (Priestley 1937).
A prime example of Coast live oak woodland must have been the site of the future city of Oakland. Father Juan Crespi’s map made during Fages’ visit to the Bay in 1772 labels the area as Llanura de Robles, “Plain of Oaks.” Sometimes gigantic old oaks grew for miles long the bayshore and its inlets. The place was called at times Encinal de Temescal, “Oak Grove of Sweathouse,” temescal being an Aztec word adopted by the Spanish that described Indian settlement features (Bagwell 1982). Explorer-geologist William Brewer passed through Oakland in 1859 and noted: “Pretty oaks are scattered over the sandy flat” (Brewer 1860).
The young sailor Richard Dana, who in 1835 rode into San Francisco aboard a hide-and-tallow ship, called Angel Island “Wood Island” because it was covered with oaks, bays, buckeyes, and madrones down to the water’s edge, and ships in harbor could cut enough wood to last them a year out at sea. By the 1850s it was almost stripped bare. Eucalyptus from Australia was planted to supplement the wood supply (Barker 1994), a trend that continued in many coastal areas of California.
Live Oak Savannas
The open, scattered savanna form of the Coast live oak community seems to be rarer than the denser type, and has had more changes to its species diversity. It may have grown in scattered valleys and coastal flats from northern California to Baja.
The lost oak savannas of Berkeley, urbanized and cleared away except for a few old trees scattered among houses and city streets, remain in memory: the “Hanging Oak” used to grow on Allston Way, where a horse thief met his end. It was cut down in 1980. From Founders Rock the view in 1860 was of a vast meadow dotted with ancient oaks (Berkeley History 1983). One Berkeley street had a grand old live oak for years right in its midst, taking up a small island with asphalt around it -- cars drove on either side along the narrow avenue. Out-of-town folks laughed when I showed them this relict tree allowed to stay in the middle of a road, but locals planted a new oak at the same spot when the ancient tree fianlly died.
William Brewer found at Nipomo Ranch Coast live oaks “with great spreading branches, gnarled and knotted trunks,” beautiful with dark green foliage (Brewer 1860). Salinas Valley originally had large live oaks scattered between Salinas and Castorville, 2 to 3.5 feet in diameter. They were cleared for strawberries, artichokes, and rangeland (Gordon 1974).
Seeking out the oak savannas that have not been engulfed by urbanization, I found most of them with weedy understories of introduced European grasses and forbs under the shade of their spreading boughs. But relict natives can be found.
In San Luis Obispo, San Diego, and Orange Counties I found remnants of Purple needlegrass (Stipa pulchra), Nodding needlegrass (S. cernua), California melicgrass (Melica californica), Sandberg bluegrass (Poa secunda), native annual foxtail fescue (Festuca microstachys), California oatgrass (Danthonia californica), and other natives typical of the original open grasslands of California around the oaks, and directly under the oak canopies, grasses that require slightly more moisture: Mountain brome (Bromus marginatus), Blue wildrye (Elymus glaucus), Torrey melic (Melica torreyana), and Bentgrass (Agrostis pallens). Scattered shrubswere also present, such as Toyon, Blue elderberry, and California sagebrush (Artemisia californica).
Father Crespi’s description of Santa Barbara in August 1769 gives a clue to possible species present:
“We went over land that was all of it level, dark and friable, well covered with fine grasses, and very large clumps of very tall, broad grass, burnt in some spots and not in others. The unburned grass was so tall that it topped us on horseback by a yard. All about are large tablelands with big tall live oaks (I have never seen larger), and many sycamores as well. We have come across rose-patches in such great amounts that the plains here were full of them in many spots” (Timbrook et al. 1993)
Giant wildrye (Leymus condensatus) may be the grass he speaks of. Patches of this coarse rhizomatous grass can grow higher than my head -- it could well be described as “very large clumps of very tall, broad grass,” as Timbrook and his colleagues (1993) suggest. In January 2004 I traveled to the Santa Barbara region to gather information for a reconstruction painting of the city, using Crespi’s description as a starting point, and my own field notes of relict vegetation to fill out the picture. Sure enough, as I drove down Highway 101 from the north and entered the narrow coastal terraces below the Santa Ynez Mountains, I was immediately struck with the abundance of Giant wildrye, growing on open grassy slopes and flats, at the edges of sage scrub patches, and amidst scattered live oaks -- just as Crespi had described. I stopped in several areas to take photographs, sketch the patterns of vegetation, and take notes of my observations. I noticed a few Purple needlegrass bunches in open areas as well, probably indicating the matrix of grassland that the tall wildrye grew in during past centuries. Despite areas of cattle grazing, shrub invasion, roads and houses, the area north of Santa Barbara shows a good relict landscape that remarkably has survived to current times. I wondered if this was a unique “lost habitat,” a Giant wildrye-Coast live oak savanna type that may have occurred on other areas of the immediate coast. I have seen a few Giant wildrye patches in open spaces around Berkeley, so perhaps centuries ago a similar community grew on East Bay flats.
What kept these savannas so open? Wildfires played a large role in savanna formation as we shall see. Grazing may also be an important process in keeping the oak communities open. In northern Baja California, ecologists found that Q. agrifolia Valuable mosaics of oaks, grass, and shrubs attract many kinds of wildlife. Lark sparrows, for instance, prefer edge habitats in live oak parklands and savannas, where they nest on the ground and perch in trees and shrubs. Their population in California oak lands may have declined since the 1960s as habitats are removed or degraded, and biologists advocate using this bird as a “focal species” for monitoring conservation efforts -- when the Lark sparrow’s ecological requirements are met and it appears to be breeding successfully, then other species will benefit including the oaks themselves (CalPIF 2002). grows from acorn to tree poorly even under slight grazing pressure by cattle, which maintains open parks of old trees. Remote from cattle, stands are dense and of mixed age (Minnich and Vizcaino 1998). Speculation: did elk in presettlement times help to maintain the live oak savannas that used to be common along the coast? Large old trees are present even in the early mission illustrations.
Valuable mosaics of oaks, grass, and shrubs attract many kinds of wildlife. Lark sparrows, for instance, prefer edge habitats in live oak parklands and savannas, where they nest on the ground and perch in trees and shrubs. Their population in California oak lands may have declined since the 1960s as habitats are removed or degraded, and biologists advocate using this bird as a “focal species” for monitoring conservation efforts -- when the Lark sparrow’s ecological requirements are met and it appears to be breeding successfully, then other species will benefit including the oaks themselves (CalPIF 2002).
Interior live oak
The Interior live oaks (Quercus wislizenii) grow commonly in mixed oak woodlands in the North and Central Coast Ranges, and Sierra Foothills above the Blue oak zone where they form savannas. They were once dominant along rivers and streams flowing from the Sierras into the Central Valley, but there has been much damming and clearing for agriculture in this zone and only remnants remain (Pavlik et al. 1991).
John Fremont left us with several descriptions of the Interior live oak habitats. In March of 1884 on Cosumnes River he described the level country as “covered with groves of oak trees, principally the evergreen oak, and large white oaks.” Toward the Stanislaus River he recalls an “open grove of live oaks, which, in form, were the most symmetrical and beautiful we had yet seen in this country. The ends of their branches rested on the ground, forming somewhat more than a half sphere of very full and regular figure, with leaves apparently smaller than usual.” On March 3, 1884, his party left the foothills following a trail. The country was now “smooth and grassy; the forest has no undergrowth, and in the open valleys or rivulets or around spring heads, the low groves of live oak give the appearance of orchards in an old, cultivated country. Occasionally we met deer....” Live oaks formed “a continuous grove” at Coloma along the American River. A grassy sward extended to the edge of the river, and the air was fragrant with flowering shrubs; “...the most beautiful valley in which we had ever traveled...” said Fremont (Bohn 1969).
Edwin Bryant in 1846 visited the Rancho del Paso near Sacramento on the north bank of the American River: “We passed through large evergreen oak groves, some of them miles in width. Game is very abundant. We frequently saw deer feeding quietly one or two hundred yards from us, and large flocks of antelopes” (Woodward and Smith 1977).
In the Sierra foothills I have found highly diverse woodlands in which Interior live oaks thrive.
Sampson (1944) found Purple needlegrass to be the most widespread perennial grass in Interior live oak-Blue oak foothill woodlands with scattered manzanita in northern California counties such as Tehama, Shasta, and Colusa. After burns, the native annual Small fescue (Festuca microstachys) would appear and increase, then decline after the fifth year.
In the North Coast Range this diverse mixed woodland may be joined by Madrone (Arbutus menziesii), and California fescue (Festuca californica) as an understory to the oaks.
In the higher canyons of central California, such as along Mines Road in the Diablo Range (Alameda County) I have seen Interior live oak growing with Blue oaks scattered in a grassland with Purple needlegrass (Stipa pulchra) and Sandberg bluegrass (Poa secunda) relicts, with some Black sage, California sagebrush (Artemisia californica), Mugwort (A. douglasii), buckeye, and Blue elderberry (Sambucus mexicana).
canyon live oak
The Canyon live oak is the most widely distributed oak in California, being found in moist shady canyons with Bigleaf maple (Acer macrpohyllum), California bay (Umbellularia californica) and Tanbark oak (Lithocarpus densiflorus), steep slopes and rocky summit scrublands, mixed oak woodlands, and conifer forests.
In canyons of the San Bernardino Mountains, for example, Canyon live oaks form extensive closed-canopy stands intermixed with chaparral and conifer forests of Big-conespruce (Pseudotsuga macrocarpa) and White fir (Abies concolor). Interior live oak (Quercus wislizeni) may also be present, especially on ridgetops. Many sites are prone to periodic severe fire. After fire, most oaks regrowby vegetative sprouting (Conard 1987). Many Canyon live oak shrublands and “sprout-thickets” in southernCalifornia apparently are the result of frequent fires (Keeler-Wolf 1995, Griffin 1988).
In northern Baja mountain ranges Canyon live oak grows on steep exposed ridges and peaks on the upper edge of the chaparral belt, in mixed conifer forests, and in dense montane chaparral with manzanita (Arctostaphylos patula) and Snowbrush (Ceanothus cordulatus), all subject to local fires every 50 to 70 years. Most ignitions are by lightning, and stands of chaparral and Canyon live oak are usually destroyed and later resprout (Minnich and Vizcaino 1997). Similar patterns may have been the norm in places such as the Merced River Canyon just below Yosemite Valley, where Canyon live oaks form dense low woodlands with chaparral and Ponderosa.
Canyon live oaks growing in montane forests of the Sierra Nevada and northwest ranges typically grow on steep slopes and shallow rocky soild, often with Ponderosa pine (Pinus ponderosa), Doug-fir (Pseudotsuga menziesii) and Sugar pine (Pinus lambertiana). In the Klamath Mountains, the fire interval was estimated to be about every 11 years (ranging from three to 55 years). A 1987 fire was generally ground-hugging and of low to moderate intensity -- Canyon live oaks were little affected, having sparse, discontinous fuels under their canopies. Only a few small patches had stand-replacing crown fires (Skinner and Chang 1996).
At Dogwood Pond in the North Coast Range, a mid-Holocene maximun of inferred Canyon live oak pollen was found. Oak pollen, perhaps also Canyon live oak in large part, from Tule Lake and Lilly Pond in Mendocino National Forest shows an increase beginning at 7,000 BP, peaking a 5,000 BP, then declining slightly to the present (Byrne, Edlund and Mensing 1990). Like the California black oaks in Sierran samples, Canyon live oak was apparently also favored in places during the Xerothermic phase, and may have moved upslope and northward of its present range.
Impressive sights in California are the grand old Valley oaks dotting the grasslands, towering upward then outward with shapely enormous curving limbs. The Valley oak is the largest North American oak, reaching 120 to 150 feet tall and with a trunk diameter of 9 feet (Bonnicksen 2000). These oaks send deep tap roots down to permanent ground water under the dry plains, as well as extensive lateral roots that can reach 70 feet long just under the ground. These huge trees can reach 500 years of age.
Early settlers called it “swamp oak” or “water oak,” a name indicative of the habitat favored by these trees: floodplains and valley floors that were sometimes subject to winter overflows of their rivers or streams. Early visitors to the state wrote much about this eye-catching tree; more than any other oak it earned their admiration.
William Brewer in his travels around California in 1860 and 1861 commented often on Valley oaks. At Nipomo Ranch he likened the scene to a fine park, with large oaks scattered, green grass beneath, and a profusion of wildflowers. The Valley oaks had large limbs in great curves, 30 to 50 feet long, almost touching the ground. One close to Brewer’s camp had a crown over 100 feet in diameter, a trunk 15 feet in circumference, and lichen hanging from every branch. At Carmel he found the “roble” here very fine, one specimen attaining 26.5 feet in trunk circumference, another 6 feet in diameter, with branches spreading 75 feet each way. Two deer were seen. On the Pacheco Plain, ”California white oaks” were grand, scattered, and often spreading to 100 feet in crown diameter (Brewer 1860).
The British ship H. M. S. Sulphur in 1837 traveled 150 miles up the Sacramento River to explore. Her captain described the scene: “Oaks of immense size were plentiful. These appeared to form a band on each side, about three hundred yards in depth, and within (in the immense park-like extent, which we generally explored when landing for positions) they were seen to be disposed in clumps which served to relieve the eye wandering over what might be described as one level plain or sea of grass.” At times the crew noted fires in some stands of trees and brush along the river, describing how the natives set fire to the bases of large oak trees to help gather acorns (Bonnicksen 2000, Sampson 1944).
In the 1830s and 40s visitors to Sacramento noted immense oaks six, seven, and eight feet in diameter, some rising 60 feet before expanding into a crown of enormous branches. One tree was estimated to be 125 feet across its spreading crown. But woodcutting reduced them: one steamer used a cord of wood an hour to get from San Francisco to Colusa (Storer 1965).
Valley oaks seem to grow in two community types: dense river-edge woodlands as described above, and open savannas out on the plains and hills. One of the most famous Valley oak savannas was the Kaweah Oaks of the southeastern San Joaquin Valley. Jepson (1910) had a correspondent who remembered “...four hundred square miles of Valley Oaks...” on the alluvial soils along the Kaweah River. The wide rich plains east of Tulare Lake supported savannas of immense oaks that at times grew so densely as to form closed canopy woodlands that hindered the passage of settlers’ wagons (Preston 1981). On other spots the oaks formed “most lovely groups, masses, and single specimens” (Nordhoff 1872, in Preston 1981).
Out West Magazine could not say enough about the wonders of this place. By the Kings River delta, on rich valley soil, was the Laguna de Tache grant, having a “scattering growth of magnificent oak trees, giving it the appearance of an English park.” What may be a description of Creeping wildrye (Elymus triticoides) growing in rhizomatous fields with the Valley oaks, as it does commonly today, is given when the author speaks of a remarkable “perennial growth of green grass” in “broad park-like stretches of green pasture land.” Wildflowers were abundant. So good was the grass here that thousands of cattle were grazed on the grant, brought in from as far as Nevada, Arizona, and New Mexico. By 1899 the old rancho was subdivided and planted with corn, alfalfa, hay, grapes, and orchards (Harris 1902). Immense relict trees in Fresno and Tulare Counties suggest these fields of oaks must have been impressive.
An 1854 railroad surveyer near Cache Creek stated: “This timber belt is composed of the most magificent oaks I have ever seen. They are not crowded as in our forests, but grow scattered about in groups or singly with open grass-covered glades between them.... There is no undergrowth beneath them, and as far as the eye can reach when standing among them, an unending series of great trunks is seen rising from the lawn-like surface” (Griffin 1988).
The park-like nature of the Valley oak savannas across the state was noticed over and over by passers-by. On the Santa Clara Valley plains along the southern edge of San Francisco Bay Captain George Vancouver in 1798 observed, “We arrived at a very pleasant and enchanting lawn, situated amid a grove of trees.... For almost twenty miles it could be compared to a park which had originally been planted with the true old English oak; the underwood that had probably attained its early growth, had the appearance of having been cleared away and had left the stately forest in complete possession of the soil....” (Griffin 1988). Indeed, the local tribes had probably been setting low ground fires for thousands of years here to keep the savanna open.
“The long inhabitation of the country by the Indians and the peculiar local distribution of the Valley Oak in the rich valleys is in some way connected. These oak orchards, of great food importance to the native tribes, indicate plainly the influence on the trees of Indian occupancy of the country. The extent and nature of the relations of Indian tribal culture and the habitat of the oaks cannot yet, if ever, be completely defined, although it is clear that the regular spacing of the trees is a result of the annual firing of the country....”
--Willis Lynn Jepson, botanist, 1923.
Trying to reconstruct the original complete Valley oak savanna community with its native understory species is a tough prospect, but relicts can still be found. In Walnut Creek, for example, I saw enormous old Valley oaks on flatlands with remnants of Creeping wildrye (Elymus triticoides) under them. This grass must have been the dominant understory species in places such as valley bottomlands in the Coast Ranges, floodplains in the Central Valley, flats around and under Valley oaks, and up onto low hill slopes. Sedges (Carex) grewin wetter spots. On drier hills various bunchgrasses grew next to the oaks. At Sebastopol, I found a possible hint of what parts of the Sacramento Valley looked like: lush floodplains of large Valley oaks had a grassy understory that flooded in winter and dried out in the summer heat. Lush green stands of four-foot high Reedgrass (Phalaris arundinacea) grew on short-grass flats of Meadow barley (Hordeum brachyantherum). Creeping wildrye (Elymus triticoides), bentgrass (Agrostis exarata), Sedges (Carex), rushes (Juncus), spikerushes (Elecharis), and nutsedges (Cyperus) also grew in the valley wetland.
Researchers have noticed evidence of limited regeneration by Valley oaks since the early 1900s in parts of the state. What grows under the oaks today may be quite important:greedy annual grasses induce severe water stress on Valley oak seedlings, enough to kill them. Soil moisture is lower in introduced annual grasslands than in native perennial grasslands. Wild oats (Avena fatua), a European invader, grow rapidly in February and March, reducing available soil moisture; but Purple needlegrass (Stipa pulchra), a native bunchgrass,grows more slowly and uses less water. Valley oak seedlings also grow most rapidly in February and March, so they directly compete with annuals such as Wild oats for soil moisture. The Stipa phenology instead seems to complement oak seedling growth (Danielsen and Halvorson 1991).
Not all localities are showing this negative trend, however. Along the Feather River in Sutter County good recruitment is occurring in the mesic riparian areas. Here, a large seed reserve in the soil allowed many seedlings and saplings to grow slowly, waiting for a gap to open up in the forest (Knudsen 1987).
Flooding of the great Sierran rivers in the past, as they emptied their waters out onto the valley lowlands, may have given Valley oak seedlings the chance to put on a growth spurt. Researchers at the Cosumnes River Preserve in Sacramento County found that oak seedlings needed soil moisture in order to grow well -- irrigation of planted seedlings in fields allowed them to grow fast. The age structure of oaks in the riparian woodland also correlated seedling establishment to river flood events (Meyer 2001). Water is ever important in summer-dry California.
I mention the gray-and-white colored Swainson’s hawk (Buteo swainsoni) here because it used to nest abundantly in tall Valley oaks and cottonwoods in the Central Valley, and scenes of groups circling slowly upwards and dispersing over broad golden savannas must have been commonplace. The Central Valley historically had 1,000 to 2,000 pairs, but in 1984 only 280 pairs were found from Fresno to Chico. California has had an estimated 90% decline in nesting pairs since 1900.
In fall large gatherings of hundreds of these summer hawks circled about over the plains, then sailed south of the border forming columns of migrants past the southern California peaks. What a sight that must have been. It was said to be the most abundant migrating hawk in places such as the Transverse Ranges (Bloom 1984). Today I treasure glimpsing even one of these hawks, although fortunately more places such as The Nature Conservancy’s Cosumnes River Preserve are harboring excellent Valley oak habitat for these raptors, and their future appears better.
The Ever-changing Woodland
The stars of the black night sky outlined the barely visible crowns of Blue oaks, Poorwills called their name softly, hidden, the dawn light washing over the eastern horizon. Then the morning chorus started up: a clamor of birds calling and singing to greet the sun. California thrashers, towhees, Lesser goldfinches, and Acorn woodpeckers sang simultaneously among the oaks. The dusky blanket of dark gradually lifted, awakening the landscape with warm air and soft morning light.
Hiking through a Blue oak savanna in the early morning was a delight to the eyes, the subdued gray-blue rounded leaf canopies dotting the yellow grasslands in summer. Western fence lizards (Sceloporus occidentalis) and later a Southern alligator lizard (Elgaria multicarinata) climbed up the gray-furrowed oak trunks. As I walked through the woodlands and savannas in Mount Diablo State Park I noticed a single Blue oak seedling less than a foot high in the dry grass.
Constructing a picture of the structure and composition of the Blue oak woodlands and savannas before European contact was ever on my mind as I hike through the oak ridges and valleys, looking for clues and taking notes on the plant and animal associations I find. No one knows how the pre-contact Blue oak habitats looked. My paintings and descriptions are speculative.
The early travelers give us only general descriptions such as that of John C. Fremont as he crossed the Calaveras River in the year 1884: ”This place is beautiful, with open groves of oak and a grassy sward beneath, with many plants in bloom; some varieties of which seem to love the shade of the trees, and grow there in close fields” (Bohn 1969).
Although the grass component of the Blue oak savanna has been drastically changed by the spread of European annual grasses during the 18th and 19th centuries I have still been able to discover clues as to the original makeup of the native groundcover by examining hundreds of Blue oak habitats and searching for native remnants. They are in fact fairly common, and I think a good idea of the original matrix for the oaks and wildflowers of the savannas can be reconstructed.
Often I could detect differences between grass species growing under the canopies of Blue oak trees and those in the open. Some of the bunchgrasses that especially favored the shade of Blue oaks included Blue wildrye (Elymus glaucus), which was common and often formed dense patches under the oaks, California melic (Melica californica), Mountain brome (Bromus marginatus), and Bentgrass (Agrostis pallens). In rare instances I found Idaho fescue (Festuca idahoensis) growing under Blue oaks, as near Redding in northern California, and near San Miguel in the South Coast Range. California fescue (F. californica) seems to be exclusively a mesic shade species, which prefers the cover of the various oak species. Studies on Hastings Reserve showed that vegetation under the oak crowns grew faster and produced almost twice the biomass of vegetation in the open. Herbs also matured later and had a higher nutrient content due to the oak leak litter (Griffin 1988). Open grassland species that I observed growing around and also freely under the oak canopies included Prairie junegrass (Koeleria macrantha), Sandberg bluegrass (Poa secunda), the native annual Small fescue grass (Festuca=Vulpia microstachys), Big squirreltail (Elymus multisetus), and Small-flowered melic (Melica imperfecta).
Purple needlegrass (Stipa=Nassella pulchra) is mainly an open-grassland species, growing next to Blue oaks, but occasionally I have seen bunches under canopies, even right next to the trunk. Nodding needlegrass (S. cernua) seems to be found almost wholly in the open between oaks in savannas. Creeping wildrye (Elymus triticoides) can be found in patches on open flats with deep soils or in low areas. I also occasionally met with the dry-land bunch rushJuncus tenuis in the oak savannas.
Forbs were abundant in the spring and summer in the savannas and shrubs are often scattered throughout. Other oaks, and Gray pines (Pinus sabiniana) often mixed in.
But since the 1980s many observers noticed subtle clues hinting at changes in the seemingly pristine Blue oak wildlands. What ecologists call the “age structure” of the woodland was skewed: on my hikes I often saw only seedlings and old trees but a distinct lack of middle-age saplings, or woodlands with no seedlings at all. If this pattern is continued into the future, the old trees will not be replaced as they die. What is the cause of this pattern? That is still a mystery. Numerous range ecologists, paleoecologists, and botanists have been trapsing out into the field to study the situation, adding pieces that help to fill out a picture. Proposed explanations for the lack of young trees include cattle grazing, grazing by native herbivores such as deer and rodents, insect predation, fire suppression, competition from introduced annual grasses, and climate change. This is a typical example of the complexity that confronts the historical ecologist, and the difficulties humans face when trying to understand such a long-lived entity as a tree.
Researchers tried to solve the mystery by looking at the early stages of the young oaks. Some found that Blue oak seedling populations may be large but are ephemeral, with high mortality rates. If a seedling can reach the sapling stage it has a higher chance of survival as it sent its taproot down deep into the often dry soil (Muick and Bartolome 1987, Matsuda and McBride 1986). Others noticed that Blue oak seedlings were constantly present in the oak understory of their Sierra Foothill study site. Fire and sheep grazing had little effect on their survival. But no saplings were found (Allen-Diaz and Bartolome 2001).
Rodents were the most important predators of acorns and seedlings, mostly pocket gophers, as well as mice and voles (Davis et al. 1990). But are these small mammals enough to cause wholesale population changes in a woody species? Probably not. Cattle and deer caused small trees to have a browseline at roughly 4.5 feet, and could retard growth of the oaks and keep them shrubby for 30 years. Protection from browsing allowed the trees to grow the tallest in some studies (Bartolome, et al. 2001, Mensing 1992). “Seed-caching corvids”-- Scrub jays for instance, may be largely responsible for increasing or maintaining woody plant populations, and they apparently are doing their job well. Something is happening after the acorns reach the ground and sprout.
Other “plant detectives” found that dry winters killed many oak seedlings just after they sprouted from their acorns, but that if the surrounding cover of introduced annual grasses such as Ripgut brome (Bromus diandrus) was pulled out the oaks seedlings sprouted in larger numbers and their roots grew more (Griffin 1971, Davis et al. 1990). In Mediterranean Spain and Portugal, oaks savanna was favored when periods of severe grazing reduced the competitive and thirsty annual grasses, allowing trees to grow upwards. The age structure of this oak population reflected periods of overgrazing and undergrazing (lack of native tule elk) in the past, and no period was apparently abnormal for the range of variation of the landscape (Grove and Racham 2001).
One of the most picturesque Blue oak savannas is found around Lake Berryessa in the dry inner North Coast Range of Napa County, a relatively pristine place despite the reservoir that exists there. At a quiet picnic ground deer, House finches, Nuttall’s woodpeckers, Bushtits, and Western wood-pewees sung in the oak branches over a layer of dry yellow grass. I noticed many Blue oak seedlings on the bare ground along the receding lake shore, along with the diminutive native annual grass Foxtail (Festuca microstachys). Here, few introduced annual grasses grew, although they were common nearby in the main oak savanna: Wild oats and Soft chess (Bromus mollis). Perhaps the low level of competition on this scoured reservoir edge allowed both native annual grasses and Blue oak seedlings to thrive.
Competition from mature trees themselves can inhibit sapling growth: in Mediterranean Europe, ecologists found that existing large trees in a savanna could monopolize the underground soil space, filling the soil with their roots even when the above-ground area has gaps between the trees (Grove and Racham 2001). Young trees had a difficult time getting at the water supply. Again, in summer-dry climates water may be key to maintaining thirsty oaks.
Other researchers turned from seedlings to look at the woodland as a whole, the “stand age structure” of a population of trees. At the huge Tejon Ranch in the Tehachapi Mountains in Kern County, ecologist Scott Mensing (1992) did a stand age analysis, taking small cores from trees and comparing their annual ring counts. These showed that successful recruitment (young individuals making it to maturity) occurred historically until 1900; after that no new trees grew to adulthood. The lack of recruitment presently may be due to a natural cycle or a response to environmental changes from European settlement, but the picture is unclear. From 1570 to 1850, recruitment of trees was fairly regular. A dramatic increase occurred in the 1850s and 1860s, but only 9% of present trees have grown since 1864. The oldest tree was found to be 412 years, and even small stems (less than 9 inches in diameter) were over 100 years of age. What clue does this pattern point to?
The reconstruction of oak savanna and woodland ecology is complicated by the effects of climate on tree growth. Short-term climate changes have a definite impact on Blue oaks: during drought, seedlings often die back and few germinate. But during a following moist period many seedlings will germinate, and older sprouts will regrow.
Long term climatic cycles may play an important role. Favorable climates have been proposed as prerequisites for successful recruitment; Blue oaks and Coast live oaks are regenerating more successfully in moister geographic areas and more mesic, shadier sites. If recruitment is cyclic, then we have information only about the most recent episode during the late 19th century settlement period, which is associated with major disruptions of the many factors that could influence oak establishment (Bartolome et al. 1987). Poor recruitment today could be due to less favorable spring rains now than in the past, or the disastrous droughts that plagued the early 20th century -- possible signs of Global Warming.
Extreme climate events may be more important than shifts in averages. Oaks may have rapid recruitment in short-term wet periods. Severe droughts in the Southwest have been known to topkill oaks, which later resprout and recover. Pulses of woody plant recruitment may result from brief periods of high soil moisture. Mesquite savannas in Texas, for example, grow in clusters; during dry periods more clusters die. During average and above-average rain years new clusters form and existing clusters expand. Fluctuations are visible over time (McPherson 1997). But that is the key: reconstructing what is happening to the trees over a long enough period of time to actually reveal the changes.
Is the savanna a remnant of the Little Ice Age? Interestingly, Mensing’s recruitment data show that Blue oaks most successfully gained new trees during the 1850s -- just as Sierran glaciers reached their maximum extent in 1850 to 1855 (Stine 1996). Both glacier size and oak recruitment have since shown a steady parallel decline. Long periods of greater rainfall during the last few centuries may have favored oak regeneration, and what we are seeing today could be a long term cycle of drying, of coming out of the wet period that ended roughly in the last decades of the 1800s; this dry period may be naturally less favorable for maintaining oak savannas, and may be one consequence of Global Warming in California.
In the strangely parallel world of Mediterranean Iberia, oak savannas look strikingly like California in places, with Prickly oak (Quercus coccifera), Live oak (Q. rotundifolia), and Cork oak (Q. suber) trees scattered in a summer-dry grassland that has also had a history of fire and grazing. Where the soil moisture is sufficient some areas are infilling with young trees as goats and sheep are removed. Other areas show no recruitment. An area may have trees 90, 210, 240, and 570-year-old in clusters, but no intermediate ages -- these apparently represent years when circumstances (plentiful late springs rains, a preceding fire, and disease among the browsing goats) conspired to favor growth of trees. Large areas of oak savanna in Portugal have an age structure that could date the trees to a high rainfall period in the 1880s and 1890s. Ecologists A. T. Grove and Oliver Racham (2001), who have been reading the vegetation and land for clues in their fieldwork for decades, admit that the historical ecology of Mediterranean areas is not easy to study due to the episodic nature of their ecologic processes. There is no equilibrium model that land managers can strive for -- the same thing does not happen every year.
Back at the Tejon Ranch, Scott Mensing next looked at the fire history of the woodland, dating the scars left by flames on the trunks, scars which were then healed by subsequent growth of wood. Blue oaks survived the fires well. They have thick bark, an adaptation to resist burning. Those that are crown-scorched resprouted leaves as quickly as two weeks later. Smaller trees, under about 8 inches in diameter, were often topkilled (where the trunk dies), but they also often resprouted vigorously from the base to grow a new trunk. In one study 93% of Blue oaks survived two years after a fire (Haggerty 1990). In Mensing’s fire scar research one tree had 7 fire scars. Scars were regular prior to the 1860s, and periodically increased in occurrence about every 10 years. From 1843 to 1865 the fire interval was every four to five years. Fires were most numerous in the 1850s. From 1864 to the 1920s there was a complete absence of fire scars.
Prior to European arrival, Blue oak recruitment was low but regular and no problem existed to halt woodland replenishment. Four Mexican land grants were established in the Tejon area in the 1840s, and European settlers began arriving in 1853; Fort Tejon was built by the U.S. Army in 1854. Young oaks were unusually successful during the 1850s. Was this due to a change caused by European land use, or a coincidental climatic or natural environmental change? In 1865 General Edward Beale bought and consolidated the Mexican land grants here and moved 14,000 sheep onto his new ranch. In the 1880s he exchanged them for cattle, which have been on the Tejon Ranch ever since. Cattle grazing may have decreased the fuels necessary to maintain ground fires, thereby allowing the oak canopy to increase in density. More fires were recorded in the 1930s, but by then the oaks were large enough to withstand ground fires. Mensing could not determine from his study the effects cattle grazing had on the oak population.
James Bartolome, a range ecologist at U. C. Berkeley has been studying the problem for years. He believed that new fire-stimulated growth on saplings could be retarded by the hungry muzzles of browsing deer and cattle. Perhaps protection from these herbivores would allow small trees to grow to large size (Bartolome et al. 2001). I wondered if the 1850s phase of many fires on the Tejon Ranch ‘flooded’ browsers with so many sprouts that a large number escaped chewing to grow to maturity?
The historic fire return interval for Blue oak habitats in general in California is speculative, and estimates range from an average of every 8 to 25 years before 1900, and every 78 years after this date (Gruell 2001, Anderson, Barbour, and Whitworth 1998). More study will be needed to tease out the story of how fire affects oak growth and woodland structure by looking at history and records of long ages of time embedded in the oak landscape itself.
I have been thinking a lot about the causes of change in the Blue oak lands, in order to develop accurate paintings of pre-settlement scenes (at least best-guess hypotheses presented in visual form), and I have come to the conclusion that Nature present us with multi-faceted and interconnected processes operating often simultaneously. There is no one answer. Many factors in the environment are likely involved with the changes in oak woodlands. Fires kept rodent populations down, perhaps allowing more seedlings to become established. Long-lived trees could afford to wait for the rarer combinations of good acorn years coupled with wet winters and low browsing pressure (Pavlik et al. 1991). Blue oak establishment could be episodic. James Bartolome and his colleagues (Bartolome et al. 1987) determined that only 18 new trees might be needed each decade in a favorable rain period to continue a stand of 600 trees per hectare (one hectare=2.47 acres).
Thus we may be living in a time when oaks are not reproducing, whether for “natural” reasons or because of a century of altered landscape practices, and our own generations are too short to see the oak’s big picture. Whether the oak woodlands and savannas of California continue far into the future will require more evidence to determine, gathered by plant detectives looking at the long-term processes of competition, herbivory, climate change, and wildfire. Your observations now could be invaluable a hundred years in the future.
Little Oaks of SoCal
A true California endemic, the Engelmann oak (Quercus engelmannii) grows from Los Angeles County south to northern Baja west of the deserts. Its leaves have a bluish color but the tree is not related to the Blue oak; it is apparently related to several Mexican oaks of arid summer-rain climates (Nixon 2002).
The Engelmann oak used to grow between Claremont, Pasadena, and Pomona on deep valley clay soils and on the foothills of the San Gabriel Mountains. A few still grow in the Huntington Gardens and at Los Angeles Arboretum, but to see their natural community one must now head south (Griffin 1988, Lathrop and Arct 1987, Pavlik et al. 1991).
Usually mixing in with Coast live oak (Quercus agrifolia), Engelmann oak grows in a wide band through the south coastal counties. Some grow on the Perris Plain, but most grow in the foothills of San Diego and southwestern Riverside Counties (Scott 1990). In San Diego County they are found on rolling hilltops and foothills, sometimes in pure stands. In pre-settlement times there was an estimated 80,500 acres of open oak woodlands in the interior. Recently many have been invaded by housing tracts or cut to make avocado orchards (Oberbauer 1990).
This small rounded tree becomes dominant on only a few places: the Santa Rosa Plateau, Mount Palomar, and Cuyamaca Mountain (Scott 1990). The Nature Conservancy bought the Santa Rosa Plateau Preserve in 1984, saving it from a planned massive urban development. I have visited this plateau in Riverside County, California, and took journal notes.
The oaks on the plateau form a savanna and open woodland in wide-spreading grasslands. Searching the preserve I found Purple needlegrass commonly in the open grasslands, but invasive wild oats and mustards were abundant.
On the plateau Coast live oaks are more sensitive to moisture loss, and so usually germinate in more mesic sites such as the north sides of rocks. Engelmann oaks, on the other hand, tolerate more aridity, and can live on hot, dry, open areas. Their roots grow down deeper to reach soil moisture before sending up a shoot (Snow 1990).
Lathrop and his coworkers (1990) found a lack of young Engelmann oaks on Santa Rosa Plateau, and most of the rare seedlings were found under the canopy of nurse trees. As with other oaks in California, recruitment is a problem for this oak, and altered fire ecology may be playing a part.
Mature Engelmann and Coast live oaks are not affected by a fire; usually only the lower branches are scorched, and they resprout after a few months. If enough fuel is present under the canopy, the entire crown may burn, but it will resprout abundantly. Saplings destroyed by fire will stump-sprout even within a few days (Lathrop and Osbourne 1990).
California black oak
The sweet-smelling acorns of the deciduous black oak were the among the most favored by many of the people of California before European arrival -- the nut meat is light-colored and tasty, as I finally discovered after waiting for a local grove to produce a crop. (These oaks produce an acorn crop every two years, but masting is usually poor, with good years only every six year intervals.) Collecting some, I made acorn bread from the ground flour and indeed it had a pleasant aroma and nutty taste unlike anything I had ever eaten; a rare bit of original California cuisine.
California black oaks (Quercus kelloggii) occupy many different habitats in California, and it was a learning experience to explore and discover the huge landscape diversity of these oaks.
Black Oak Woodlands
In the North Coast Ranges California black oak often grows in diverse moist mixed forests. At Anadelle State Park in Sonoma County, mixed California black oak woodlands are common and still show a diverse native grass assemblage in openings and glades where more sunlight could reach the ground. In the central Coast Range, the most common native understory plants accompanying black oak are California fescue (Festuca californica) and Blue wildrye (Elymus glaucus).
On the west slope of the Sierra Nevada, California black oak grows in mixed conifer forests. Brewer in his travels mentions that Big Oak Flat was named for a grand tree 10 feet in diameter, that later was undermined and killed (Brewer 1860). Just above the Blue oak zone in the Sierra foothills a distinctive black oak savanna may develop, more open than black oak woodlands, and with a green sward of Bracken fern (Pteridium aquilinum) and grasses below. Such savannas exist today in Yosemite Valley, and once grew in the now-flooded Hetch Hetchy Valley just to the north. Black oaks are also found in small groves and mixed forests on the Modoc Plateau of northeastern California mixing with Great Basin sagebrush and juniper communities.
Changes in the Woods
Black oaks may be recruiting less in the Coast Range, Cascades and southern California than in the Sierras; old trees are apparently being replaced by new trees most successfully in the northern Sierras (Muick and Bartolome 1987).
In places in the Sierras black oaks have declined as conifers have grown ever denser and shaded them out -- acorns need sunny situations to germinate and grow well (Garrison, Otahal, and Triggs 2002). The black oaks stump-sprouted after logging. Some stands had continuous regeneration from acorn to tree, while other stands grew up in pulses.
These sunny places that allowed black oaks to mature were often created by low-intensity ground fires that travelled through the mixed conifer forests of the Sierras about every 10 to 25 years, keeping them open (Kauffman and Martin 1987, Skinner and Chang 1996).
Experiments with burning at Blodgett Forest Research Station in El Dorado County and in the Quincy area of Plumas County showed that low intensity fires killed only the smallest oaks. More fuels and high intensity fires killed a large number of the older shrub-sized oaks. Two seasons later the burned sites had two to ten times more seedlings appearing than on unburned sites. Fire may improve the soil by destroying pathogens and fungi and decreasing “damping off” of seedlings (where overly moist soils cause molds to attack and kill the roots). Fires may topkill black oaks, which often resprout on the crown, along the trunk, or from the base.
Numerous acorns-caching animals help the oaks to colonize newly burned areas: jays, Western gray squirrels (Sciurus occidentalis), and Douglas tree squirrels (Tamiasciurus douglasii).
Paradoxically, at the same time recruitment of oaks is sometimes lacking in some places, other evidence points to an increase of oaks from their pre-contact levels. Gruell (2001) found in his repeat photography study of the Sierra Nevada that California black oaks were greatly increasing in density over the past 75 to 100 years. An 1867 photo from Placer County at 2900 feet elevation, for example, shows a scattering of black oaks in an open, patchy Ponderosa forest. Low chaparral is present in some openings. A 1993 photo from the same site, however, shows closed stands of black oak, manzanita, and buckbrush, and second-growth pines growing more densely than originally. From an open pine-black oak forest, the modern vegetation has become a thicket due to fire suppression.
“A fire-glow in the distance, and then the wavy line of burning grass, gave notice that Indians were in the valley clearing the ground, the more readily to obtain their winter supple of acorns and wild sweet potato root -- ‘huckhau.’”
--H. W. Baxley in Yosemite Valley, 1865.
The Miwok managed the valleys of the Sierran west slope with fire, and prescribed burning was part of the ecology of places like Yosemite Valley for the last 3,000 years or longer. Charcoal lies in every layer of a small oxbow pond along the Merced River in the Valley back to the beginning of the record 700 year ago (Anderson and Carpenter 1991).
Galen Clark, caretaker of Yosemite in 1894 commented that the Indians’ purpose “was to annually start fires in the dry season of the year and let them spread over the valley to kill young trees just sprouted, and keep the forest groves open and clear of all underbrush, so as to have no obscure thickets for a hiding place, or an ambush for invading hostile foes, and to have clear grounds for hunting and gathering acorns“ (ibid.).
Keeping the oak groves “clean” could mean the use of regular burning to remove pest insects, such as the California acorn weevel (Curculio unifornis) that infests acorns. Larvae feed on the acorns, then drop out of the trees to the leaf litter below to pupate in the soil. Burning woody debris, fallen bark, and layers of leaf litter may have kept their populations down(McCarthy 1993, Powell and Hogue 1979).
In addition, when hunting deer in Yosemite, Miwok men set many small fires in the forest around the meadows to drive deer out into the open. They were shot with bow and arrow as the hunters waited in hiding. Deerbrush patches were particularly sought out for burning, as deer congregated about them (Lewis 1993).
Interestingly, the ancient Romans, like people in the oak savannas of modern Spain, used a somewhat reminescent way of life to that of Old California, roasting acorns and making acorn bread from their oaks, eating pine nuts, living off acorn-fed pigs that roamed the oak svannas freely, practicing sheep transhumance and burning the savannas to benefit their herds (in California the numerous deer and elk herds also fed much on acorns and burnt-over pastures), “pollarding” the trees for fuelwood (cutting branches off living trees rather than clear-cutting them, a practice which was said to increase the acorn crop), and cultivating grains in shifting fields around the trees (in California the wild grasses provided a similarly abundant annual crop of seeds for pinole) (Grove and Racham 2001).
While a university student I enrolled in an enlightening class called “Pollen Analysis” taught by plant geographer Roger Byrne. During field trips to the Sierras we camped by small lakes in dark pine-oak forests. Lake Moran, really a pond, for thousands of years had pollen wafting into its waters from the surrounding trees, pollen now preserved in the layers of ooze at the bottom. We rafted out onto the middle of the lake, then lowered a metal bore down into the bottom muck, drilling it in, and pulling it back up. Inside was a long cylinder of mud, and if carefully preserved from contamination and taken back to the lab, it would produce a time-lapse view of the changing numbers and types of pollen grains from the local vegetation.
In the lab we placed washed samples of the mud onto glass slides and with microscopes counted pollen types using standard identification guides. With this information we could calculate percentages of each pollen type in different time periods, and infer vegetation. Bits of organic matter throughout the core could be sent to a carbon-dating service, thus giving the sequence marker dates.
Although oak pollen is unfortunately not diagnostic as to species, we could infer that oak pollen in association with other plants was California black oak. Thus a window could be opened into deep time, looking at a rough picture of oaks back into the last Ice Age.
Pollen, macrofossil, and charcoal from cores taken by Roger Byrne and his associates at Lake Moran in the Sierras, presently at the upper elevational limit of California black oak in mixed conifer forest, showed a decrease in mesic forest trees such as Mountain hemlock (Tsuga mertensiana) and Lodgepole pine (Pinus contorta) and an increase in oak and Ponderosa pine with increasing charcoal (indicating fires in the forest), from 10,000 to 5,000 BP. This is probably showing the retreat or disappearance of glacial forests in the early Holocene and gradual formation of drier-adapted forests with warming. At Gabbot Meadow in the Stanisalus River drainage of the central Sierra, pollen showed that oaks were more common during the period from 9,000 to 5,000 BP than at present -- a warm, dry phase is indicated. At Exchequer Meadow, oak climbed in elevation slightly above its present limit from 9,000 to 7,000 BP (Byrne, Edlund and Mensing 1990). Oak pollen may be indicating the onset of the warm dry Xerothermic phase of the Holocene, when temperatures peaked; after this period temperatures fell slightly to today’s mean.
What I learned from reading the pages of pollen-layers in the mud was that through the thousands of years of oak history in the forests there is no “typical,” there is no “average,” there is no one snap-shot of time that could be called “normal.” As climate changes gradually and imperceptibly, the woodlands and forests respond.
Northern California-Oregon Oaks
Oregon oaks remind me of blue oaks and valley oaks. They occupy a transition area of high biodiversity, edemism, and topographic complexity in northwestern California mountain ranges.
“’What bush is this?’ the questioner pointing, or perhaps even having hold of a specimen of Quercus dumosa. And in nearly all instances I have had to hunt up an acorn-cup still fast to the shrub, in order to back up my assertion that it was an oak. I am willing to admit -- from personal experience long ago -- that it is a novel sensation for one who all his life long has walked underneath the oak trees to come here and tramp along a trail bordered with a forest of oaks no taller than his head!
“Chaparral comes from chaparro, the Spanish name for live oak; and from chaparral, or perhaps direct from chaparro, comes chaps -- those hide appendages which the vaqueros wear to protect their legs from the hostile scrub-oaks.”
--Francis M. Fulltz, The Elfin Forest of California, 1923
As we transition from discussing oak habitats to chaparral, the various scrub oaks form the perfect link, being both oaks yet also important members of California’s chaparral scrublands. The identification of scrub oaks has been confused lately, but is coming to a resolution. What botanists once thought were a few species are apparently numerous types that sometimes look outwardly similar. Because their identification is important to the historical ecology of this group, I present summaries of each scrub oak species that occurs in the state, based on work done by Nixon (2001) and Hickman (1993):
Q. palmeri (Palmer’s oak)-- in older literature it is labeled Q. dunnii. This scrub oak is rare in California and more common in Arizona and Baja California. It prefers summer rains, and its fragmented Califormia distribution may indicate attrition over the millions of years that a Mediterranean climate has developed in California (Nixon 2001). It occurs in semi-desert chaparral or pinyon-juniper woodland, 3000-5000 feet in elevational range, along the inner Peninsular Ranges and Transverse Ranges, as well as the inner Coast Ranges from Santa Barbara to San Benito Counties. The northernmost population is in the eastern Diablo Range in Alameda County (Pavlik et al. 1991).
Q. dumosa complex-- the pattern of variation in acorns, trichomes (hairs on the underside of the leaves), and habitats of this oak suggest five species may be present. Two species are currently recognized as being related:
Q. dumosa (Nuttall’s scrub oak)-- The 19th-century wilderness naturalist Thomas Nuttall originally collected this type of scrub oak along western shores of the state on low coastal hills of loose sandstone or granites, in “soft chaparral” (now known as coastal sage scrub). It is a rare form ranging from Santa Barbara County to northern Baja California. Urban develpoment has destroyed most populations of this scrub oak, ironically lost in a nomenclatural haze that prevented it from being recognized as threatened, it fortunatelty survives in such places as Torrey Pines State Park in San Diego County. It is found on bluffs, headlands, and hillsides by the ocean (Nixon 2001, Pavlik et al. 1991). See Figure XX for a diagramm of this scrub oak’s habitat.
Q. berberidifolia (Scrub oak)-- this common and typical scrub oak of the “hard chaparral” of chamise and manzanita, this species is found on higher and more interior localities of the Coast Ranges, in the Transverse and Peninsular Ranges, and Sierra foothills north to Tehama County. Formerly called Q. dumosa, it is an important member of the chaparral, growing from 6 to 15 feet tall (Nixon 2001, Pavlik et al. 1991).
Q. durata (Leather oak)-- this scrub oak is restricted to serpentine and diabase outcrops, the only North American oak to have this requirement (Nixon 2001, Wells 1962). It ranges from the Klamath Mountains, Coast Ranges south to San Luis Obispo and Santa Barbara Counties, and the San Gabriel Mountains. In the Sierra foothills it ranges from Nevada County to El Dorado County (Pavlik et al. 1991).
Q. cornelius-mulleri (Muller’s oak)-- the first of the dumosagroup to be recognized as a separate species. It is found in dry washes and slopes in chaparral on desert margins and in pinyon-juniper woodlands of San Bernardino, Riverside, and San Diego Counties, to northern Baja California. It can be seen in Joshua Tree National Park and on the western edge of Anza-Borrego Desert State Park, and along the eastern side of the San Bernardino, San Jacinto, and Laguna Mountians. It is associated with California juniper (Juniperus californica), Red shank (Adenostemma sparsifolium), Sugar bush (Rhus ovata), and at its lower limit, Creosote (Larrea tridentata) (Nixon and Steele 1981, Nixon 2001, Pavlik et al. 1991).
Q. john-tuckeri (Tucker’s oak)-- once considered to be the same as desert scrub oaks in Arizona, this species has recently been seggregated from those oaks, and found to be closer to Q. berberidifolia. It is found in interior desert margins in chaparral thickets and pinyon-juniper woodland on the east side of the Tehachapi Mountains, South Coast Range, Transverse Range, and northern San Gabriel Mountains (Nixon 2001). This scrub oak locally dominates chaparral in the Diablo Range and Santa LuciaRange (Griffin 1988).
Q. turbinella (Shrub live oak)-- a true desert scrub oak of Arizona to Texas and northern Mexico, found isolated in California only in the New York Mountains of the east Mojave Desert, in granitic pinyon-juniper woodlands that apparently recieve much summer rain (Nixon 2001).
Scrub oaks grow in a large variety of vegetation types, from chaparral, to woodland, to grassland. Scrub oak chaparral with Q. berberidifoliaoften grows on slopes above 3000 feet in southern California mountains, and in the northern part of the state above the chamise chaparral zone on slopes and ridges where the soil is suffieciently deep. Usually the canopy is so dense as to exclude understory plants. Other shrubs are often present with scub oak (see Figure XX for a typical North Coast Range chaparral community with scrub oaks).
After fires, Scrub oak (Q. bereberidifolia) in chaparral resprouts quickly, but does not seem well adapted to grow from acorns on scorched ground -- very few seedlings are usually seen on recent burns. Zedler (1977), in searching for them in San Diego County, found Scrub oak seedlings only in old unburned stands 90 years old, in deep leaf litter. The seedlings were in groups as if germinated from animal caches.
In San Benito and Monterey Counties Q. berberidiflora on long-term range study plots of Blue oak savanna had a native bunchgrass understory of Sandberg bluegrass (Poa secunda) in 1932. By 1990 the cover had changed to annual introduced Foxtail barley (Hordeum leporinum) and bare gound. The plots had a history of cattle grazing and drought. The scrub oak cover had increased among the Blue oaks, many forking and becoming larger, but no seedlings were seen (Holzman and Allen-Diaz 1990). Did fire historically keep scrub oaks less dense in mixed woodlands?
In the Garin Hills of Alameda County, Safford (1995) found Quercus durata and Q. palmeri growing in the middle canopy layer of Coast live oak (Q. agrifolia) woodlands.
Searching out scrub oak communities myself, on the arid interior slopes of the mountains in Los Padres National Forest at about 4000 to 5000 feet I examined low mixed woodlands of Tucker oak (Quercus john-tuckeri), Pinyon (Pinus monophylla), and California juniper (Juniperus californicus) to record which natives still grew with them in the flood of annual grasses from Europe. In these open scrub-woods were fine examples of manzanita (Arctostaphylosspp.), Whipple yucca (Yucca whipllei), California buckwheat (Eriogonum fasciculatum), Blue elderberry (Sambucus mexicana),Pine bluegrass (Poa secunda), Prairie junegrass (Koeleria macrantha), Desert needlegrass (Achnatherum speciosum), Squirreltail grass (Elymus elymoides), native annual Foxtail fescue (Festuca microstachys), Wild onion (Allium sp.), and Penstemon (Penstemon eatoni).
On some low hills surrounding the arid Cuyama Valley in the same area I walked among scrub oak savannas with much evidence of old burns -- charred Tucker oak branches, resprouted from their bases and six feet high. They grew scattered in an open grassland with the natives Nodding needlegrass (Stipa cernua) and Sandberg bluegrass (Poa secunda). I pondered about whether this represented a relict community typ of fire-adapted scrub oak savanna, perhaps once more common in California.
These few examples of scrub oak communities in California give only a hint of the probable diversity of the group, in the present and in the past. More study needs to be done to discover the changes that have occurred in these “elfin forests.”
to paint an oak