January 02, 2014

The Saguaro

The saguaro cactus has been called the monarch of the Sonoran Desert. In its old age, it is has majesty and personality, with odd, somewhat human shapes ~ shapes that inspire all kinds of imaginings, especially in such a harsh climate.

The Sonoran Desert is a surprisingly lush region, full of life: cacti, animals, birds, trees and shrubs. Still, it is one of the hottest and driest places in North America. During most years, less than 30 cm of rain falls here annually. Summer temperatures often exceed 40 degrees. It is not unusual for several months to go by without a drop of precipitation. Temperatures during winter nights often reach freezing.

Life for a saguaro is difficult. It begins with a seed no bigger than a pinhead. One saguaro cactus can produce tens of thousands of seeds every year; as many as 40 million in its lifetime, which could be 200 years.

Out of the millions of seeds produced, only a few survive to adulthood. In most cases, young saguaros have the best chance for survival if they grow under or near other trees, shaded from intense sunlight, blanketed from the winter cold, and hidden from rodents, birds and humans.

Saguaros grow slowly, and mostly in spurts during the summer rainy season. After one year, a seedling may measure only 5 mm. After 15 years it may be 25 or 30 cm. At about 30 years saguaros begin to flower and produce fruit. At 50 years the saguaro can be 2 metres tall, and after 75 years it might begin to produce its first branches, or arms. These branches begin as balls, then extend out and upward.

At 100 years of age the saguaro could be 8 to 10 metres tall. The grandest sizes are reached after 150 years when they tower over most other things in the desert, at a stately 15 metres. Give or take.

Woodpeckers and flickers drill nest holes in the trunks or branches. Sometimes they make and reject several cavities in one season before settling in one to raise their family. This  provides holes for other birds and honeybees, unable to drill holes in the cactus. Insulated, the holes are up to 10 degrees Celsius cooler in summer than the outside.

Saguaros die naturally of old age. They also die of other causes. Animals eat the seeds and seedlings. Lightning and wind kill large saguaros, and droughts weaken and kill all ages. Humans have been a problem for the saguaro too. Livestock grazing, widespread for one hundred years beginning in the 1880s, devastated some cactus forests. Poaching has been an issue with the theft of saguaros for use in landscaping the yards and driveways of the wealthy.

All photos by Jim Murray. 
Copyright 2013.

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