Native Oaks and Urban Sprawl

A handsome survivor on farmland at Gait, California; but are its days numbered? Photographs by J. Trumbley, from Native Oaks: Our Valley Heritage.

A handsome survivor on farmland at Gait, California; but are its days numbered? Photographs by J. Trumbley, from Native Oaks: Our Valley Heritage.

For almost twenty miles it could be compared to a park which had originally been planted with the true old English oak… the stately lords of the forest in complete possession of the soil.

Captain George Vancouver describing the Santa Clara Valley near Belmont in 1798. Quoted in Native Oaks Our Valley Heritage, 1976.

Vancouver and other early travelers recorded their enthusiasm for oaks and the beauty they contributed to the western landscape. In 1850, Bayard Taylor wrote, in El Dorado, of the importance of oaks to the sweltering inland city, Sacramento.

The original forest trees, standing in all parts of the town, give it a very picturesque appearance. Many of the streets are lined with oaks. The emigrants have ruined the finest of them by building camp-fires at their bases, which, in some instances, have burned completely through, leaving a charred and blackened arch for the superb tree to rest upon. The destruction of these trees is the more to be regretted as the intense heat of the summer days, when the mercury stands at 120 degrees, renders their shade a thing of absolute necessity.

Later, during his journey from the counties of Santa Barbara, San Luis Obispo, and Monterey to the Salinas Valley, Charles Nordhoff in California: for Health, Pleasure, and Residence, published in 1872, witnessed the region’s park-like setting.

All this landscape was beautified by interminable groves of live and white oaks… low-branching, gnarled, huge, and as artistically disposed in groups and single trees as though the most skillful landscape gardener had planted them… a sufficient defense of the natural school of landscape gardening.

Today both men could locate reminders, on maps of western states, of the oak forests that once flourished: Oakesdale, Oak Harbor, Oakville, Oak Grove, Live Oak, Oakland, Oakridge, Oakview, Big Oak Flat, Oak Knoll and similar names are often all that remain of the trees’ original territory. After over a century of development, the number of native oaks in Sacramento could now be counted, were he here, on Taylor’s fingers. Charles Nordhoff would discover that the natural school of landscaping is at the mercy of property owners and developers and governmental agencies and that the few oaks remaining in urban areas stand alone, surrounded by asphalt in shopping centers, or marooned in amassments of single and multi-family residences.

Little concern is shown for this tree on a development site near Sacramento; its chances of survival are slight.

Little concern is shown for this tree on a development site near Sacramento; its chances of survival are slight.

The trees that Vancouver, Taylor and others admired may have included valley oak (Quercus lobata), blue oak (Q. douglasii), interior live oak (Q. wislizeni) and others. Identification of some is made difficult by the many hybrids that occur among them. The valley oak most resembles those in Europe and is likely to have reminded travelers of home. Some, relics of groves, but now isolated specimens, are magnificent trees a hundred feet tall and three hundred years old. Many old trees have hollow trunks and no proper count of annual rings is possible. The famous Hooker oak in Chico, California, destroyed by a storm in the late 1970s, is estimated to have been 1,000 years old.

Recognition of the significance of what is lost with these old oaks is spreading. Some city and county planning agencies attempt to preserve them by prohibiting their removal from development sites. But attempts often fail because the root systems of these great trees are easily damaged during and after construction. Over millions of years oaks have become well adapted to their environment and the slightest disturbance can kill them.

With few exceptions, native Americans were innocent of conspicuous consumption in their dependence upon oaks. Indians used the trees for food, medicine and firewood, but seldom destroyed them. With the arrival of white settlers, however, eradication began. Oaks were used more intensively for fuel, and were sacrificed for building and in the clearing of pasture and crop lands. More recently, flood control levee maintenance and growing urbanization have eliminated many more.

Somehow, though, the natural assets offered by oaks to urban areas were overlooked. Their huge canopies and large limbs are handsome and provide privacy, shade, and windbreaks. Their roots prevent erosion. The trees also absorb noise and improve air quality. In addition, drought-resistant oaks require little maintenance. Using knowledge and caution, developers and home-owners can retain these amenities.

Other species native to the region such as western hemlock (Tsuga heterophylla), Douglas fir (Pseudotsuga menziesii), black cottonwood (Populus trichocarpa), Oregon ash (Fraxinus Iatifolia), and the coast redwood (Sequoia sempervirens) can usually withstand minor alterations to their immediate surroundings. But an established oak’s survival depends upon retaining undisturbed the soil directly above its roots. Any change in this delicate environment weakens the tree’s root system and may kill it.

While germinating, a young oak’s long, vertical tap root provides sustenance. As the root system matures, smaller feeder roots extend in a shallow, lateral pattern away from the crown’s heavy main roots, and the oak’s canopy broadens in the same way. These lateral roots lie approximately twelve to eigh­teen inches below the ground and eventually radiate beyond the tree’s dripline (a circle on the ground corresponding with that of the leaf canopy) to obtain water and nutrients from the topsoil. So extensive a root zone close to the surface is especially vulnerable to damage. Almost any disturbance to the soil between the trunk and a foot or so beyond the dripline can injure roots vital to the tree’s survival. Heavy machinery used near the tree compacts the soil, making it less porous. Water is less able to reach the roots, and the exchange of gases between roots, soil and atmosphere, as important to the tree as water, is prevented. Filling near the tree has the same effect.

Victim of a developer’s good intentions near Carmichael, California. The attempt to preserve the tree came to nothing because grading was taken too close.

Victim of a developer’s good intentions near Carmichael, California. The attempt to preserve the tree came to nothing because grading was taken too close.

Grading damages roots and exposes them to desiccation. Soil drainage is altered by grading and the tree may be deprived of water, or what may be worse, provided with too much. Excess water encourages soil fungi that are fatal to oaks. Thus the futility of many attempts to retain fine specimen trees in emerald urban lawns.

Paving buries the tree’s roots and dams water to and from it. Alternatives to asphalt and concrete are pervious surfaces, such as shallow layers of bark, gravel, or porous bricks with sand joints. All manmade covering should be kept dry in summer and free of debris. Paving within the dripline can sometimes be successful if an aeration system is incorporated within the paved surface. However, the greater the area under the canopy left in its natural state the longer the tree will survive.

Other changes, such as cuts, within an oak’s immediate vicinity, not only expose the tree’s roots, but also obstruct its natural moisture supply by causing dehydration in the soil. Conversely, ponds accumulate in cut areas and drown the tree. Trenching often causes death by severing much of the tree’s root system. If trenching under the canopy area is unavoidable, one trench should be used for all utilities. The canopy, however, will probably require a corresponding pruning, and this is best done by a tree specialist. Boring a hole for services does not rupture the roots as severely and should be employed, if possible.

Under natural conditions, oaks obtain sufficient moisture from precipitation and mountain runoff, with little, if any, water supplied during warm months. They can, to some degree, tolerate deep and intermittent summer irrigation beyond the dripline. Shallow watering causes abnormal root development too near the soil surface and contributes to the risk of uprooting during winter storms. Irrigating close to the base promotes root diseases. Summer irrigation may take three months or thirty years to kill a century-old native oak, but eventually will destroy it.

On well-drained soil, lawn or garden plants can sometimes be cultivated under an oak, especially if there is a natural grade away from the tree. Plants tolerant of shade and dry summers should be used and placed at least six feet beyond the trunk. But in areas of adobe or clay soils water drainage is slower and the risk of impeding aeration greater. Here native oaks have a greater chance of survival with no under-planting.

Trees of poor growth that are not victims of disease or insect attack may be helped with applications of balanced fertilizer. Over-fertilization must be avoided for an excess of succulent new growth encouraging mildew is easily stimulated. If it becomes necessary to replace the nutrients normally supplied by the decay of leaves and other litter, fertilizers are less likely to weaken the tree if confined to the area just beyond the dripline.

Pruning of dangerous or diseased branches and dead wood is a necessity for oaks near buildings. Indiscriminate thinning or pruning, however, produces excessive new foliage. Ideally, an oak should be cut back only during dormancy; in winter for deciduous trees and July and August for evergreen. A sealing compound for cuts is mainly cosmetic. There is little evidence that compounds prevent the entry of disease-producing organisms.

If insects or diseases attack, a professional tree specialist should be consulted. Large numbers of oak moths or galls, or the presence of pit scale, are warnings of the need for advice. Insect attack, improper soil aeration, and warm-weather watering make oaks susceptible to diseases, the most common of which are crown rot, Armillaria root fungus, heart rot, and wet wood slime flux. Obvious changes in the tree’s appearance, such as excessive sprouting; sticky, faded, or wilted foliage and branches; premature leaf loss; and an unusual number of dead branches and twigs, are signs of disease.

Regeneration is becoming rare for some oaks. One example is the valley oak (Quercus lobata) which inhabits the fertile valleys of California. When the acorns drop in October, they are consumed by mice, squirrels, birds, insects, and other urban wildlife. Because the oak population is declining in urban areas, food for the animals is limited and quickly depleted. If an acorn germinates, however, a bulldozer or lawn-mower probably destroys the seedling.

Not only urban but rural areas too are affected. Cattle and sheep join wild animals in grazing valley and hillside range land. Acorns are eaten and seedlings trampled.

A campaign is needed to preserve not only ancient trees, but young ones too. Areas must be found where they may be left undisturbed for the three- to five-hundred years needed for their development. Some may survive to replace their ancestors. Native oak seedlings, which should be transplanted from urban, not primitive, areas, do especially well in large urban yards if planted away from structures and protected from predators. In centuries to come, later generations can, with imagination, visualize the vast oak forests left by the Indians for Vancouver to observe in 1798, Taylor in 1850, and Nordhoff in 1872.

Through care (although, in some cases, neglect is better) and knowledge, native oaks are compatible with urbanization and can be retained. They have provided so much for so many and surely deserve more than just place names on the map. They deserve appreciation and, above all, preservation.