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Tough Trees : Finding Hardy Plants to Weather the Drought

March 21, 1991|DIANE CALKINS

By summer a lush lawn may be a luxury of the past, but who can imagine a landscape without trees?

In dry times even ordinarily hardy trees, especially those accustomed to regular irrigation, can succumb. Once weakened by drought, they become susceptible to pests, disease and pollution.

Watering of trees is one of the few outdoor uses of water that will be allowed under the water conservation plan adopted a week ago by the San Diego County Water Authority.

The regulations, which go into effect April 1, permit trees and shrubs to be watered using a bucket, drip irrigation, or a hand-held hose that includes a shut-off nozzle. Sprinklers may be used to irrigate trees and shrubs planted in turf and ground cover, but only once every two weeks.

Although most native and non-native trees and shrubs suitable to our environment should be salvageable, some thirstier species may go the way of turf. And, by the time rain returns in earnest, Southern Californians may have learned to rely more strongly on plants naturally suited to this climate.

Actually, the Southern California landscape, including North County, does not offer a naturally tree-rich milieu, says R. Mitchel Beauchamp, author of "A Flora of San Diego County, California."

This is especially true if certain types of trees are excluded: those found above 3,000 feet (like the big cone Douglas fir on Palomar Mountain) and along streams (like the willow and California sycamore along the San Luis Rey and Santa Margarita rivers). These trees do well in the specific environment where they are already established, but do not thrive in the Mediterranean scrub flora communities most common in North County.

Although everyone has his or her own favorites, a few trees and shrubs emerge as definite winners for a variety of landscaping situations from Del Mar to Oceanside, Carlsbad to Escondido.

In this climate, just determining what is a tree can be tricky. A number of plants that are technically shrubs grow to the size of trees.

Trees are defined in P. Victor Peterson's book "Native Trees of Southern California" as woody plants "at least 10 feet high with a distinct stem or trunk not less than 2 inches in diameter and, except for unbranched yuccas or palms, with a more or less well-defined crown."

About the oak, there is no doubt.

"What is more characteristic of the California landscape than the oak," writes Sharon Johnson in "Living Among the Oaks," a publication of the University of California Cooperative Extension. "Round-crowned oaks dapple the rolling hills, solitary monarchs shade our rural roads, and valley giants stretch skyward in banners of leaves and lichen. Past and present-day travelers have stopped in awe of our native oaks, and countless photographs and memories are framed by their spreading, weather-worn branches."

California Indians prized the oak beyond its appearance, and some researchers estimate that more than 50% of their diet consisted of acorns, which were ground and used for mush or cakes. Oak trees offer shelter as well as food to birds and small mammals.

The coast live oak, an evergreen tree with low spreading branches, and the Engelmann oak, which is often mistaken for the former, are particularly suitable for North County. Because of its smaller size, the Engelmann oak makes more sense in the average garden.

Also known as the mesa oak, the Engelmann grows naturally in a limited area, primarily in western San Diego County.

Dedicated to preserving the Engelmann, a small group of admirers led by the late Frances Ryan planted trees grown from acorns in Escondido. Of particular note are the trees at the Ryan Oak Reserve, including one that is nationally registered, and at Oak Glen Elementary School.

Biologist Brad Burkhart, revegetation manager for ERC Environmental and Energy Services Co., developed a class on native plants that he now teaches at Quail Botanical Gardens. Of the 20 species of Pinus native to California, he singles out several: the torrey, Coulter, digger and Bishop pines.

Although the Torrey pine has suffered losses because of the drought at the Torrey Pines State Reserve, home gardeners do not have to hold back a little supplemental irrigation as the rangers at the park are required to do.

A sprawling tree when exposed to offshore winds, Pinus torreyana may reach a height of 50 or 60 feet if planted away from the ocean.

"The Coulter pine is used to a little bit higher elevation but can do well in lower elevations, and the Bishop is potentially useful near the coast," says Burkhart.

Sometimes described as a tree you can see right through because of its sparse long needles, the digger pine was scorned by the early settlers, especially since it had little value as lumber. The Indians, however, relied on the tree for its seeds and cones. The settlers often lumped all California tribes together, calling them Digger Indians, and may have given the Pinus sabiniana that name with equal contempt.

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