GARDENING\Springing to the defense of deciduous plants.

Byline: Joshua Siskin

Southern Californians have one unifying prejudice: a dislike for deciduous plants. Deciduous plants are those perennials that have the audacity to lose their leaves at some time during the year. For most deciduous trees and shrubs, this annual abscission takes place in winter.

Several theories have been advanced to explain the aversion, in our part of the country, to temporarily leafless plants. Many of us came here from cold climates where trees and shrubs commonly lost their leaves in the fall; naked trees are a vivid reminder of that cold, old place, that past life. Perpetually green trees represent the endless youth to which Hollywood stars and the people who live in their shadows aspire.

Evergreen plants, especially those that bloom in our city all year long, are culturally compatible with L.A.'s freeways, cellular phones and supermarkets that never close. The constant color of the bougainvillea - no less than the constant whir of high-tech, nonstop urban life - is by turns invigorating and exhausting, exciting and a bore.

Watch the emergence of leaves and flowers on plants that were only dormant for several months, but seemed dead. You wonder how you could have doubted the re-emergence of those distinctive leaves of your favorite deciduous trees: the heart-shaped catalpa leaf, the feathery mimosa, the maple leaved liquid ambar and the fig-leaved fig.

Another often forgotten or unappreciated foliage fact is the purplish-red or bronzish cast of certain leaves when they first open. Such colors may be seen on new leaves of both deciduous and evergreen plants, including roses, xylosma and nandina. The brightest new red, if not scarlet, leaves belong to the photinia shrub.

There are three factors or variables responsible for deciduous plants losing their leaves: day length, temperature and soil moisture level. Leaf crop is a physiological hedge against drought. In cold climates where the ground freezes, it is impossible for plants to draw water out of the earth during winter months. In such areas, plants with flimsy leaves and watery sap are deciduous. Short days and cold nights are signals to deciduous trees that the ground soon will be frozen, and now is the time to grow a special, weak layer of cells between leaf and stem that makes it possible, under pressure from the slightest breeze, for the leaf to fall.

Cold-climate evergreens such as pine, cedar, juniper, and fir have leathery, drought-resistant needles or scales. They also have anti-freeze-like chemicals in their sap that keep them turgid and vitral without need for winter resupply of water from the soil.

Deciduous plants also may be found in the desert. In periods of drought and/or cold, trees such as Mexican palo verde, acacia, mesquite and ocotillo readily shed their leaves.

The two most popular deciduous trees in Los Angeles - the white birch and the crepe myrtle - have barks that provide winter interest when leaves are gone. Three white birch (Betula pendula) on a raised mound in front of the house, to the left or right of the front door, is one of the most beloved of landscape effects, and it has been repeated ad nauseam throughout Los Angeles. A pleasing variation on this theme is to mix in a few California native water birch (Betula occidentalis), which have red trunks, along with the more common white trunk varieties.

The crepe myrtle, which is the last deciduous tree to leaf out in the spring, also is threatening to wear out its welcome in our city, as it is planted almost everywhere these days. But the wine red glow of new crepe myrtle leaves is still something to behold. Both birch and crepe myrtle are pretty, small, and low maintenance. They are economical and appropriate for the times, yet without lasting impact. They simply don't grow large enough to fall under the fabric of great trees.

The great deciduous trees of Los Angeles are trees that are native to this area, but slowly disappearing because of their size and maintenance cost: the California black oak (Quercus kelloggii), the California white or valley oak (Quercus lobata), the white alder (Alnus rhombifolia), and the California sycamore (Platanus racemosa). The California sycamore grows to 100 feet and is plagued with fungus and insect problems; it has fallen from grace, no doubt, for these reasons. Yet, to see this tree in the Beverly Glen parkway just south of Sunset Boulevard is to witness a marvel of the botanical world and to wish

your own street was lined with specimens of this very same tree.