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Sonoran Desert

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The Sonoran Desert is one of North America's most interesting deserts, with more plant and animal types than any other desert in the world. It is the wettest and the warmest desert on the North American continent. The Sonoran Desert is located in the southwestern United States and northern Mexico. In the United States it reaches from southeastern California to the western two-thirds of southern Arizona. In Mexico it includes much of the state of Sonora and the eastern shore of Baja California. It covers an area of approximately 120,000 square miles. There are some mountainous areas where frost occurs, but most of the desert is frost-free. The Colorado, Yaqui, Salt, Verde and Gila Rivers pass through this desert.

The boundaries of the Sonoran Desert are determined by the plants and animals that live in the regions. The Arizona Upland region is located in south-central Arizona and northern Sonora. It has more mountain ranges than other areas of the Sonoran Desert and is the highest and coldest region. The valleys are very narrow. Saguaro cacti are found everywhere except on the valley floors. It is the only region of the Sonoran Desert that experiences frequent hard frosts. Succulent cacti, drought resistant and thorny shrubs are common. On mountainous slopes towards the north, these plants mix with chaparral type vegetation of dense thickets and fire adapted plants

The Lower Colorado Valley is the largest, hottest and driest region of the desert, and is known for its beautiful wildflowers displays. Drought deciduous trees and shrubs are common here. Many are very thorny to discourage browsers. Toward the south the Sonoran Desert gradually merges into the Tropical Dry Thorn Forest of southern Sonora and Sinaloa.

The Sonoran Desert on the Baja peninsula is also known as the Vizcaino desert. Off-shore islands located in the Gulf of California are also part of the Sonoran Desert. The summers aren't quite as hot as the rest of the Sonoran Desert. A high mountain range shields the desert from Pacific storms and accounts for the small amount of rain that falls in the winter. Moisture and fog from the Gulf of California can be considerable, allowing epiphytes to grow on the desert plants. Many different species of succulents like agaves and yuccas grow here.

The Sonoran Desert is known for its beauty and for the amazing cacti and succulents. Some 2,500 plant species grow in the harsh conditions of the Sonoran Desert. More than 160 plant species depend on other plants, like the nitrogen fixing desert ironwood, mesquite, and palo verde trees, to germinate and grow into mature plants. These trees provide plants and animals with a habitat, food and shelter necessary for their survival. Found on the Sonoran coastal plain region, the desert ironwood is the oldest desert tree. The ocotillo has adapted to the severe climate by remaining leafless during the coldest or driest months. They grow new leaves with every rainfall, only to drop them a few weeks after the rainy spell is over. During severe drought, they even drop some of their branches. The most recognizable cactus in the Sonoran Desert is the saguaro cactus. The chain fruit cholla and teddybear chollas, pipe organ, barrel cactus, and jojoba are some other cacti found here.

Between late February and mid April beautiful carpets of annuals like poppies, lupines and owl clover cover the desert floor. These flowers depend on rainfall and this display of flowers occurs only about once in a decade. Locally a good bloom can occur every three years or so. Winters need to come earlier and be wetter than normal. Seeds of summer poppy and devil's claw germinate soon after the first rain and begin flowering only 3 weeks later. Chinchweed has adapted well to all conditions, and ranges from New Mexico into the central Mojave desert.

Herbaceous perennials and shrubs like penstemon, brittlebush, and fairy duster are less sensitive to the timing of rainfall and are more dependable bloomers than the annuals. These plants grow in small patches and don't carpet the ground with color like the annuals do however. Most herbaceous plants flower opportunistically with enough rain, and sometimes more than once. The desert zinnia will flower in both rainy seasons. Ocotillo will grow and shed its leaves three weeks later after every rain.

The Sonoran Desert, like many other deserts, was considered by people in the past to be a wasteland. Now more and more people are attracted to, and moving into the Sonoran Desert. They come to enjoy the large open spaces the desert can give them, to camp and experience the desert in their all-terrain vehicles. Unfortunately, the lifestyles of people, and the needs of wild life are often conflicting. Urbanization is spreading further into the desert every year around Tucson, Arizona. Roads bisect territories, and many animals become road-kill as they attempt to cross. Many species won't cross roads and become isolated in smaller and smaller pockets. This reduces their ability to find mates and reproduce, resulting in the extinction of that species in that particular area of the desert.

Large parts of the Sonoran Desert are still intact due to careful planning and conservation. The Coalition for Sonoran Desert Protection was responsible for getting The Ironwood Forest National Monument designated on June 9, 2000. Located northwest of Tucson this 129,000 acre area contains large stands of ironwood trees and an amazing diversity of birds and animals.

Many areas are already managed by the federal government. Organ Pipe Cactus National Monument is run by the National Park Services, Cabeza Prieta National Wildlife Refuge by the U.S. Fish and Wildlife Service, and the Barry M. Goldwater Air Force Range by the Department of Defense. All together these parks cover more than three million acres west of Tucson, Arizona. The National Parks Conservation Association proposes the establishment of a Sonoran Desert National Park and Preserve. Legislation to authorize a study of management options for the parks is pending in the US Senate.


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