Children of the Sun and Wind

Nature carefully designed the plants of our desert, making them sturdy and strong.

Drought resistant, members of the desert family use little water, conserve moisture for dry spells.

Spring rains bring desert flowers.

they live and function within the narrow confines of their rigid environment. Take the ocotillo, for example! Although drought-resistant in type, it has some of the characteristics of a drouth-evading perennial. Like the drouth evaders, the ocotillo enters its active season with the coming of the winter rains, and produces its flowers and fruits in the spring. Then, with the advent of hot, dry weather it discards its leaves and appears to be entering the aestivation stage of a drouth evader. But a summer thunderstorm soaks a stretch of desert and, look! The ocotillos in the area are bursting forth with a brand new ensemble of leaves while the true drouth evaders sleep on undisturbed. Whereas the drouth evaders become dormant with the arrival of the dry season, the ocotillo simply discards its leaves thereby greatly reducing the surface through which it can lose moisture. Its green bark takes over the food manufacturing functions of the leaves, and the plant goes into low gear. When a summer storm gives it a fresh supply of water, it puts out another set of leaves and shifts into high, only to shift back to low again by shedding these leaves when the soil around its roots dries out.

Because the leaves are the organs of plants through which most of their moisture is lost, drouth-resisting plants plug the leaks by doing away with their leaves, reducing them to small size, or covering their surfaces with some material that will reduce the outward passage of moisture. The creosote bush (sometimes called greasewood) which is one of the commonest shrubs of the Sonoran Desert, coats its leaves with a varnish-like substance that glis tens in the slanting rays of the sun and makes the plants look as if they were wrapped in cellophane. The mesquite, the hardy tree of desert watercourses where it takes advantage of the moisture of the occasional flash-flood runoff, has tiny leaflets which fold upon themselves and turn their edges to the sun thus resisting the forces of evaporation. Other plants reduce their leaf surface as much as possible, cover them with tough skin, but provide them with a mass of spongy tissue which stores water during the moist season for use during dry weather. These plants are known as leaf succulents.

Of much interest to humankind because of their weird shapes and interesting variations are the cacti. The many species of this family are abundant throughout the desert, and rep-

The ocotillo and century plant add their charm.

Present one of Mother Nature's most successful botanical experiments. In general the members of this group are stem succulents although one of the most popular, the Night-blooming Cereus (Peniocereus greggii of the Sonoran Desert) stores its reserve moisture underground. Practically all of the cacti are devoid of foliage except in the early spring when small leaflets appear. Food manufacturing functions of the leaves are taken over by the green skin of the stems, loss of moisture from which is combatted by great numbers of spines which serve to break up the movement of hot, dry air. Desert plants have more to fear from the steady sweep of parching winds than from the direct heat of the sun. So efficient are some of the cacti that their stem tissues are capable of storing enough moisture during a wet season to last them from one to three years, with an occasional sip from a summer thundershower. This provides a safety factor rarely taxed even by the long periods of drouth experienced by some portions of the Sonoran Desert.

Thus we find, living together in harmony, representatives of all three methods which Nature has fitted plants to survive in the desert. However, throughout any region are found a variety of conditions of soil, slope, moisture, exposure to sun and wind, and other factors. Since some plants are better fitted to meet one set of conditions than another, we find certain species inhabiting one type of area and other groups somewhere else. Several species commonly found growing together are spoken of as a plant association, and in the Sonoran Desert there are several of these associations each occupying localities where a specific set of conditions are dominant. As listed by A. A. Nichol, formerly of the University of Arizona, the principal associations are the Mesquite Bosques or thicket association, the Palo VerdeBur Sage-Cactus association, and the Creosote Bush-Salt Bush association. Of course these associations blend or overlap to a certain extent. Incidentally, the Salt Bush, a common plant of the alluvial flats, is often mistaken for Sagebrush which it superficially resembles. True sagebrush is a desert plant, but one typical of the Great Basin Desert farther north and is not one of the characteristic plants of the Sonoran Desert.

But what of the animals of the desert; how do they meet the conditions imposed by deficient and uncertain rainfall? How do they obtain food and water to maintain life under the restrictions imposed? Brace yourself, for the answer is that animals use much the same methods as the plants, either escaping, evading, or resisting the drouth. Animals, however, have two distinct advantages over plants, the advantage of motion and the ability to capture the moisture that the plants or other animals have stored.

During the spring and fall, large flocks of birds move along migration routes in a northsouth direction. Some kinds fly great distances with short stops to rest, while others travel leisurely attracting little attention. In the spring they go north to suitable nesting grounds where food and moisture are abundant, escaping the heat and drouth of the desert. In the fall they return to harvest the seeds of desert plants thereby escaping the rigors of the northern winter. They've gone! The threat of snow is in the sky. Those harsh-voiced V's of geese have all passed by. Long lines of ducks no more are seen on high. Along the shores of yonder ice-rimmed pond, bare willow limbs lift high, on leafless wand, last summer's warblers' nest, its builders gone. Where did they go, those flocks of field and fen? To warmer climes where seeds and bugs remain. Where suns are warm and parched earth soaks up rain. This is the land they seek, the great Southwest; a land of mesquite, cactus, food, and rest. Until, again, they hear Spring's call to nest. They come; urged from the North by chilly nights, some, like the ducks and geese, by mighty flights; others more slowly, bush to bush, and shunning heights. Some go beyond, urged on as if by fear, but others stop to spend the winter here, and seek the same old spot, year after year.

But birds are not the only escapists, for whereas hundreds of miles of cross-country travel may be required to bring the voyageur to a different clime, similar changes in temperature and (to some extent) moisture conditions may be found by traveling a relatively short distance upward on the slopes of the higher desert mountain ranges. A thousand feet vertical distance is comparable in climatic changes to a latitudinal distance of 200 miles at the same elevation. Remember, mountains lifting their heads into the cool regions of the upper atmosphere receive the blessings of moisture condensing from winds to pass over them. Thus, some species of animals living in the desert at the bases of these mountain ranges migrate upward in the summer into a belt or But birds are not the only escapists, for whereas hundreds of miles of cross-country travel may be required to bring the voyageur to a different clime, similar changes in temperature and (to some extent) moisture conditions may be found by traveling a relatively short distance upward on the slopes of the higher desert mountain ranges. A thousand feet vertical distance is comparable in climatic changes to a latitudinal distance of 200 miles at the same elevation. Remember, mountains lifting their heads into the cool regions of the upper atmosphere receive the blessings of moisture condensing from winds to pass over them. Thus, some species of animals living in the desert at the bases of these mountain ranges migrate upward in the summer into a belt or