Archive for the ‘A Natural History of the Sonoran Desert’ Tag

Arizona Upland — The Saguaro-Palo Verde Forest   7 comments

We live in the Sonoran desert. For most people, when they hear the term “desert” they picture a dry, desolate wasteland. However, the term defines a wide spectrum of diverse landscapes, plants, and animal populations.

“A concise nontechnical definition of a desert is ‘a place where water is severely limiting to life most of the time.'” (A Natural History of the Sonoran Desert) The Sonoran desert is divided into seven subdivisions based on the diverse vegetation found in 100,000 sq. miles that include much of the Mexican state of Sonora, most of southern Arizona, southeastern California, and most of the Baja California peninsula.

Tucson and most of the Pima county area are in the Arizona Upland subdivision, which is the highest and coldest part of the desert — also called the “saguaro-palo verde forest.” The diversity of this area is partly explained by the two equal rainy seasons.

More and more, biologists are concluding that the Arizona Upland’s climate, vegetation density, and biodiversity resemble a thorn scrub biomes more than desert biomes, which might explain why many refer to this area as the “lush” desert. By any name, this is a very special place. Still many people who visit and/or move to Tucson complain about what they see as a lack of seasons, when in fact the Arizona Upland has five seasons: summer monsoon; autumn; winter; spring; foresummer — they’re just more subtle.

The defining form of the Arizona Upland is the saguaro cactus. I first fail in love with the area and its giant saguaro cactus in the late ’60s, during which time I read of the imminent demise of this iconic symbol of southern Arizona. Upon my return, some forty years later, I learned that such impending doom was no more than a modern myth, although soundly refuted refuses to die. As written in A Natural History of the Sonoran Desert, “The misinterpretation might be analogous to a situation in which extraterrestrials briefly visit the earth and collect a sample of people from a nursing home.”

Like with most species of desert plants there is an ebb and flow in the ecosystem. Declines are often caused by severe freezes or droughts. Since much of the west has been in a ten-year drought, it is not surprising that a decline may currently exist. “In the occasional wet years, mass recruitment reverses the trend of decline with a reproductive boom. In the case of saguaros, these episodes of net recruitment seem to occur less than a half-dozen times per century in the Saguaro National Park (west), and less often in the drier regions.” (A Natural History of the Sonoran Desert)

— kenne

Images by kenne

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