THE DESERT PALM OASIS

© By James W. Cornett, Curator of Natural Science Palm Springs Desert Museum

My introduction to the desert fan palm occurred some twenty years ago at Thousand Palms Oasis in the Coachella Valley. The sight of a lush, tropical environment surrounded by one of the world's hottest and driest deserts seemed. a paradox; it was precisely what I did not expect. Deserts are arid, yet flowing water was abundant at Thousand Palms. Deserts are also shadeless with little relief from the intense sun; yet the canopy of palm fronds in the oasis was SO dense that not a single ray of sunlight reached the ground. I was equally impressed with the abundance of birds, most of which were conspicuously absent from the surrounding desert. The oasis seemed a great hub which attracted animals from all directions. This was a place to be both appreciated and understood. With the aid of a grant from the Richard King Mellon Foundation to the Palm Springs Desert Museum, Theo Glenn, Jon Stewart and I initiated a study of the desert fan palm oases of the Sonoran Desert. For the past three years we have examined as much of the ecology of these environments as time has permitted and had the humbling opportunity of retracing the footsteps of the late Randall Henderson. From 1921 until at least 1952, Henderson, with tremendous vitality and persistence, searched out nearly every desert fan palm oasis in existence and, most importantly, wrote about them in detail. His articles, which appeared in Desert Magazine, became an important part of our research (Henderson, 1938 and 1965). Our first questions involved the status of the palms themselves. How were their numbers faring since first counted by Henderson? Had the palms withstood the severe floods, fires and droughts which had occurred over the past six decades? From reports written by Richard Vogl (1966) and Lawrence McHargue (1969), and from our own cynicism with respect to environmental trends, we anticipated that palm oases would be decreasing in both size and number. We were well aware of the lowering of underground water tables. We also knew of countless palm fires started by vandals and the invasion of the noxious tamarisk into the oasis environment. We were surprised, nearly startled, by our results. Of the 100 palm oases we revisited, 63 had more palms than when first described by Henderson. Some showed dramatic increases. Andreas Canyon near Palm Springs went from 322 palms in 1946 to 1,324 in 1984, an increase of 311%. Dos Palmas Spring, just east of the Salton Sea, had just 27 palms in 1947. I counted 308 there today. Not only did we find that the number of desert fan palms was increasing, but the number of palm oases had also increased. Though two small palm oases in the Coachella Valley had been destroyed by off-road-vehicles, at least three new ones have appeared near Dos Palmas Springs and two more in Anza-Borrego Desert State Park. Unlike many other environments, palm oases are doing remarkably well. Unquestionably the life blood of the palm oasis is water. Palms are intolerant of drought and begin to die within weeks if the soil dries out. They are thus restricted in their distribution to places where the soil is permanently moist; in canyon bottoms subjected to year-round runoff or along earth faults where underground water flows may be dammed and forced to the surface. Should runoff or seepage increase, the number of palms increases; successive years of drought can result in a decrease in the size of palm groves. In theory at least, many plant species should act as a check on palm numbers, competing with palms not just for moisture but for light and soil nutrients as well. However, Washingtonia has little difficulty in dealing with competition. Their trunks grow up to two feet per year and their extensive root systems pervade the soil leaving little room (or competitors. Cottonwoods and willows are easily pushed aside and are often eliminated. Mesquite is usually relegated to the outskirts of the oasis. Our research has failed to demonstrate that even the pervasive tamarisk shrubs can displace palms. In fact tamarisk is present in most of the sixty palm oases we have visited where palms are increasing. Time after time it is the palms which are crowding out the tamarisk. Another competitive advantage of the palms is that they are resistant to the savage effects of fire. Unlike most trees with which we are familiar, palms do not have their sensitive growth layers restricted to a ring just beneath the bark. Instead their vascular tissue is strewn throughout the trunk and most of it is protected by the insulating qualities of the wet interior wood. Though the dead hanging skirts are burned away and the green leaves are killed, the palms survive and put forth new fronds in just two or three weeks. In the devastating Palm Springs Fire of 1980, thousands of palms were charred yet only one out of a hundred was killed by fire. All of the other oasis plants are wiped out or at least obliterated to ground level by fire. Many return by sprouting from rhizomes, roots or root crowns. But ii takes at least three years before they can begin to achieve their former position in the plant community (Cornell and Zabriskie, 1981). Meanwhile the palms have produced tons of new seeds, seeds which now have an open. sunlit nursery in which to grow, uncluttered with dead palm debris and shrubs and much wetter due to the temporary absence of other plants. Palm groves not only tolerate fire, they may require it. Hidden Palms, near the center of the Coachella Valley, has burned twice in the past decade, the greatest frequency of fire in

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