SAGUARO CACTUS IS AN IMPRESSIVE PLANT

by Whit Gibbons

May 30, 2010


President Teddy Roosevelt, who developed the concept of the national park system, said, "A grove of giant redwoods or sequoias should be kept just as we keep a great or beautiful cathedral." While in Saguaro National Park near Tucson, Ariz., last week I was able to fully appreciate his point.

They don't call clusters of saguaro cactus "groves" or even "forests," nonetheless, a stand of upright plants with few limbs and no leaves dominating a mountainside at sunrise is inspiring. At a certain distance from such a stand, an observer might wonder why our national park system is preserving a landscape of telephone poles. But the close-up view is awesome, and the plant itself has qualities as singular as those of the redwoods.

Both represent their state symbolically. Redwoods are the state tree of California. Saguaro enjoys recognition as the state flower of Arizona, being so designated in 1901, more than a decade before Arizona became a state. Although nearly all Arizonans I was with carried guns, no one would dream of using a saguaro cactus for target practice or harming one of the plants in any way. A gun would more likely be used against someone who violated the sanctity of the saguaro cactus. Those impressive green giants of the Sonoran desert seem to be respected by all the residents.

Like many Arizonans, saguaro cactus themselves are armed, Many have one or two, some three or more, horizontal "limbs," which then grow vertically to create the classic captured-bandit pose. But the majority simply stand upright with no arms because it takes as many as 75 years to grow the first one. Arms on a saguaro are especially important for reproduction: the top of an arm is where the flowers are located. According to one account, a saguaro cactus takes an average of 50 years to reach maturity. In some areas, maturation can take more than 100 years and cacti can live more than 150 years. A 10-year-old saguaro may be only a few inches tall.

The saguaro cactus belongs to the cactus family, but it is the only species in its genus. This means there is no other species that is closely related or that can be confused with this spectacular plant. The tallest individuals are up to 50 feet, and the diameter can be more than three feet.

In much of the Sonoran Desert habitat, saguaro cacti are the dominant plant, towering above the agaves, chollas, and barrel cacti. The saguaro cactus has a critical role in the desert community. Gila woodpeckers and gilded flickers interact with the cactus, the only "tree" around, in the manner other woodpeckers do with a pine tree. They look for insects and excavate holes for their nests. Other birds, such as purple martins, house finches, and elfin owls, also make their nests in holes in the cactus.

Saguaro typically bloom in April and May, and I was fortunate enough to see some blooming. The best time to see the arrays of white flowers is at night, although some blooms stay open during the morning. Among the chief pollinators of saguaro cactus are bats. Of course, the bats are not being altruistic and simply helping out the cactus. The nectar of the saguaro cactus is very rich, and one scientific study found that the amino acids associated with the cactus pollen have a positive effect on lactation in some bat species. Because most of the flowers are closed up during the day, the nectar is not depleted by diurnal birds and insects and is available as a valuable nutrient source for the bats.

At 10-year intervals a census is taken of the number, sizes, and ages of saguaro in Saguaro National Park. The census is always in the same year as the U.S. Census. Since saguaro cacti do not move around and have no political agenda, a cactus population census is more reliable than a census of humans. In the last estimate, 1.6 million saguaro lived in the national park. As President Roosevelt recommended, we should strive to keep them.



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