A Haven for Desert Plants-Deserts: A Parched World-Desert Plants and Man

A Haven For Desert Plants

Ayer Lake is a man-made oasis to store water for irrigating the Arboretum's gardens. It is also home to waterfowl, waders, shorebirds and local wildlife. Two endangered species of desert fish, the Gila topminnow and desert pupfish, were introduced into the lake by Arizona Game and Fish Department.

The Arboretum protects a segment of the Arizona Uplands Sonoran Desert. In the last century, the north slopes of Picketpost Mountain were overgrazed by cattle and denuded by woodcutters. During the Arboretum's early years of operation, the area was fenced for research purposes and allowed to naturally re-vegetate.

For the casual visitor, a walk through the Arboretum is an orientation to the plants of the world's deserts and semi-arid regions. For the plant enthusiast and scientist, the Arboretum is a rare opportunity to observe and closely examine a myriad of arid-adapted plants.

A network of interconnecting trails wind through the Arboretum. Along these trails, thousands of water efficient plants from arid and semi-arid regions of North America, South America, the Near East, Africa, Central Asia and Australia arrest visitors' attention. Arid land plants may take on bizarre shapes and curious life styles that have evolved as methods of coping with dry habitats.

To walk the Arboretum's Sonoran Desert Upland Natural Area is to see a landscape radically different from our popular image of the Southwest. The Sonoran Desert supports an amazing and diverse melange of life. The surrounding desert landscapes are a mosaic of colors, shapes and textures. Here, the plant communities and riparian (riverside) areas are influenced by soil characteristics and composition, air temperature, available shade and moisture, and rock types.

In addition to cacti, there are long, spiny branched ocotillo, green-stemmed palo verde, thorny acacias, low growing mesquite, desert hackberry, and golden-flowered agaves. Congested stands of chollas contrast with the decided spacing of creosote bushes--a self-imposed method of water rationing.

The High Trail crosses a north-facing slope through native vegetation of the Arizona Upland subdivision of the Sonoran Desert. From this vantage point, one looks down on a panoramic view of Queen Creek and the canyon area. The Main Trail , dwarfed by sheer canyon walls, follows Queen Creek and emerges from the reparian or stream community to a shaded, fragrant area of plants from other arid lands. The Arboretum's dense grove of broadleaf trees, conifers and tropical-looking palms create a striking contrast to the surrounding desert scrublands. Old World pistachio, olive, common myrtle, pomegranate, bamboo-like Arundo, and date palms, below, line the pathway.

Many of these water saving shrubs and trees, such as the Canary Island Palm add shade, shelter and privacy as well as color to Southwestern gardens and yards. They also have important economic potential for many arid environments. Not only do the plants provide protective shade, they are also efficient windbreaks, soil stabilizers, and renewable sources of timber, oils, resins, and edible fruits and nuts. Towering blossoms of the Arizona mountain agave foretell its demise. After many years of growth and food storage, an agave, or century plant, sends up a single stout stem bearing clusters of flowers. A year after it blooms, the plant dies.

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Deserts: A Parched World

Desert. The word conjures up images of dry, barren wastelands of shifting sand dunes and wind-sculptured rocks. Although severely restricted by shortages of water, most deserts are not deserted. Life is there--sometimes visible, sometimes hidden. Many species of plants and animals have adapted to the precarious conditions of an arid and often shadeless desert. In terms of botanic variety, the earth's arid regions may be second only to those of the tropics.

In the extreme conditions of arid environments, plants compete for available water rather than light. Plants that can grow in deserts often do not look or act like ordinary plants. To survive in the desert, a plant must be able to live with very little water and to wait for it--months or years, if need be. The South African Lithops mimic pebbles in color and pattern. This disguise helps to conceal the plants from moisture-seeking animals.

Moisture-efficient plants have evolved special means or growth habits that enable them to resist water loss and to survive long periods of drought. The South African stapelia's squat, starfish-shaped flower looks more like a marine animal. Some species give off an odor of rotting meat that attracts flies to lay eggs in them.

Xerophytes (dry habitat plants) from different botanical families have developed similar solutions to the challenges of desert life around the world. New World cacti and yuccas, South African aloes, and North African and Asian euphorbias have thick spongy leaves or stems for absorbing and holding large quantities of water.

Not all deserts are hot year round. In some arid regions, winter can be severe and icy cold. Plants in these cold deserts must endure low temperatures as well as scarcity of water. Many of the imported arid land plants growing at the Arboretum are adapted to this part of the Upland Sonoran Desert. Cold-sensitive species of cacti, euphorbias and other succulents are given additional protection in the display greenhouses located in the Smith Interpretive Center.

Desert vegetation forms the foundation of a complex yet fragile interdependent living system. This web of life is precariously balanced on the need to conserve and to efficiently use available moisture. Water governs the growth of plants and thus the welfare of the animals and people in the world's arid regions.

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Desert Plants and Man

The lives of desert-dwelling people worldwide are closely linked with their region's vegetation. Ripened fruit of the saguaro is used in the rainmaking ceremonies of Arizona's Tohono O'odham people. The fleshy fruit is also a staple food in the diet of many desert animals. The agave is another example of a plant that has long been associated with the economy and culture of southwestern indigenous people and Mexicans. They used the agave's leaf fiber to make rope, baskets, mats, thatching and coarse cloth. Young flower stalks and fruit were eaten, and the heart of the plant was roasted as a staple food. The plant's sweet sap was fermented into intoxicating beverages.

Today, we are rediscovering the value of familiar dryland plants and are exploring new ways to capitalize on their economic and agricultural resources for the world's arid regions.

The clear wax of the candelilla is used commercially in food products. The guayule's latex is a source of natural rubber. Creams, powders, lotions and medicinal products are made from the juice of Old World Aloes.

The native jojoba's bean-like seeds yield a liquid wax used in manufacturing plastics, floor wax, automobile finishes, cosmetics and machine lubricants. It has proved to be an effective substitute for the oil of the endangered sperm whale.