Our Window on Nature

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Palm Oasis: Remnant Of A Tropical Past

Filed under: Trees — Lowell Christie -- June 8, 2007 @ 1:53 pm

PalmWhen we think of palm trees, we imagine tropical beaches and pineapples, and dancing girls shaking their hips to the rhythm of drums. Palms belong in Hawaii or Bali, or at least in the Florida Keys.

In California, however, native fan palms are surrounded by desert. Sound like a contradiction in terms? These California fan palm oases aren’t widespread, but rather are tiny pockets of vegetation, a carryover from a time when the entire area was blessed with a tropical climate.

Isolated though they are, you can still visit some of these palm oases on your next trip to the Southwest.

During the Miocene and Pliocene epochs, southern California, northern Baja, and western Arizona enjoyed warm and wet weather. Sunny skies still dominate those regions, but now water is limited to trickles and ponds. Beyond reach of the moisture, desert extends toward the horizon, giving life to a few mesquite trees, and patches of creosote bushes and bur sage.

Obviously, water isn’t widely available in this barren desert, but it sometimes percolates up to the surface through fractures along fault zones or through tiny cracks and crevices in otherwise solid rock. Sometimes, surface water collects at the base of an alluvial fan. Since the rocky alluvium eroded off of mountains in the first place, it’s not surprising that water should also seep down from the mountains and that some of it should collect in depressions in the bedrock and gradually rise to the surface.

Most palm oases, however, are found under other conditions. They are hidden away in deep gorges and canyons, where rainwater and snow melt funnel from mountain to desert. There, the passing moisture creates a microclimate that is able to support large populations of palms — sometimes numbering in the hundreds.

The California fan palm ( Washingtonia filifera) is named for its broad, fan-shaped leaves. Think back (if you are old enough) to hot summer days spent in non air-conditioned churches and halls, and picture the cardboard fans that made your hours bearable. Fan palm fronds could serve the same purpose admirably, if you were a giant. But with no one to pick them, the old fronds droop and dry, to hang around the base of the trunk until wind or fire removes them.

Mature Washingtonias may be as much as 90 feet tall, but even then, the girth of the trunk is small. Unlike true trees, the palms don’t increase much in diameter with age, so they exhibit no annual growth rings. That makes it impossible to accurately judge the age of a palm. Scientists’ best guess is that they live for a couple of centuries.

In the spring, myriad tiny flowers cluster in and amid the fronds, but by early summer, they’ve been replaced by the small datelike fruit (edible dates also grow on palms) that’s so attractive to birds and other animals. The palms provide more than food; they offer shade and shelter as well. In fact, the entire oasis teems with life.

Canyon tree frogs are the noisiest creatures of the summer. Their Johnny-one-note bleats waft into the night — love songs luring mates to a poolside orgy. Hours later, when old Sol glides over the distant peaks, lizards emerge from their burrows to search for insects or to do push-ups in the sun.

Overhead, a hooded oriole tears strings from the palm fronds. These orioles use the strands to weave their pendulous nests. They even sew the nests (without using needles, of course) to the undersides of the fronds. Hooded orioles will nest in trees other than palms, but only when absolutely necessary.

One larger animal that is much in evidence (although not necessarily visible) is the coyote. True omnivores, the coyotes eat the palm fruit as soon as it falls from the trees, making the fruit the bulk of their diet. Later, they perform the service of dispersing the seeds through their droppings.

For the last thousand years, man has also played a role in the existence of the palm oasis. Early Indians built clusters of huts in the shade of the palms, often using fronds to thatch their roofs. They didn’t intend to use these houses all year, however, because the availability of food in the desert either brings feast or famine. Living the vagabond life of hunters and gatherers, the Indians arrived at the oasis in May and June, using it as a base camp while harvesting mesquite beans, cactus fruit, and hearts of agave; then, in early fall, they moved up the slope to where acorns and pinon nuts were ripening.

Even in that early era, Indians understood how to use fire to maintain open water in the oasis. By setting fire to the groves and killing off some of the palms and most of the undergrowth, they could make sure that less water was consumed by the plants. That left more for the Indians. The palm oasis would look blackened and bare at first, but in a few months, new growth would appear.

Other animals also benefited from the burning. As fire consumed dead palm fronds, grasses, and brush, it left behind as much as a foot of ash – nutrient-rich ash, ready for recycling back into the soil. Several seasons of heavy blossoming and abundant palm fruit followed each time the oasis was burned, and that in turn brought an increase in the population of birds, small mammals, and other forms of wildlife.

The Indian villages have vanished, but birds, lizards, frogs, and coyotes still frequent the waterholes. People come, too; but now they arrive in vehicles or on foot, to spend an hour relaxing and listening to the wind whisper through the palms.

Several of California’s palm oases are easily accessible to travelers. One is situated behind the visitor center at the northeast entrance to Joshua Tree National Park, and a second, more beautiful one is a short drive or hike from Cottonwood Campground. Anza-Borrego State Park contains quite a few oases, although not all are accessible to visitors without four-wheel-drive vehicles. You’d be best off checking with a ranger about those oases. Finally, Palm Springs (well named) is home to several lovely palm oases, situated at the base of Mount San Jacinto. Local visitor centers will be happy to give you directions.


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