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Knowing Nature . . .

Arizona - Crazy Cacti and Desert Drama

April 15, 2008
Jocie Ingram

Organ Pipe National Monument photo © Dave Ingram

The so-called “spring break” (mid to late March) is seldom very spring-like. With temperatures dipping to zero, we decided to escape to southern Arizona for ten days of sun. I’ve always had a hankering to see the desert, a place as different as can be to the lush, green rainforest of coastal BC.

Our journey began in Phoenix, and we promptly left this large, sprawling city and drove south to a small town called Ajo (ah-ho), our base for exploring Organ Pipe National Monument. Someone we met on the plane couldn’t understand why we wanted to go to Ajo, since there was “nothin’ there”. We said that was exactly the reason!

Organ Pipe National Monument is at the heart of the Sonoran desert. The Sonoran is one of four major deserts in the US, and it occupies the Southwest quarter of Arizona, adjacent parts of California, and extends well into Mexico. The Sonoran is about 10, 000 years old, and due to its low latitude and altitude, is the warmest of the US deserts with the highest diversity of plants of animals.

Dry and sunny most of the year, the Sonoran receives bi-seasonal rains. Gentle rain falls over a period of days in the winter. In the summer, thunderstorms unleash intense localized downpours that may last only minutes. Soils can’t absorb all of the water, and flash floods are common. For a brief period, washes, or dry streambeds called arroyos, are transformed into rushing creeks.

Saguaro photo © Dave Ingram

The most conspicuous feature of the Sonoran desert is the saguaro (sa-WAH-ro) cactus. The largest cactus of the US, the statuesque saguaro stands up to 50 ft high and may weigh several tonnes. Emblematic of the American southwest, the saguaro has a striking silhouette made popular in cartoons and westerns, with human-like “arms” extending upward on either side of the main trunk.

Like many desert plants, saguaros are designed to conserve water. Shallow horizontal roots, spreading out from the cactus, can absorb as much as 200 gallons of water after a rain. Accordian-like pleats allow the cactus to expand and store water in its spongy flesh. The waxy green skin helps to reduce water loss, and spines shade the plant and deter animals from eating it.

Saguaros are critical to the survival of many desert creatures. Birds such as the Gila Woodpecker and Gilded Flicker excavate nest holes in the cactus. The holes are well insulated, providing protection from summer temperatures that may soar to 38 degrees Celsius and winter temperatures that may drop to freezing. Abandoned holes are taken up by elf owls, warblers, cactus wrens and many other birds.

Between late April and June, creamy white saguaro flowers (Arizona’s state flower) bloom atop the trunk and branches of the cactus. Opening after sunset, the flowers are pollinated mainly by bats. Later, the large fleshy fruits are the favourite food of many animals and birds.

Young saguaros require the protection of “nurse” plants, such as the shrub-like palo verde. It is not until a saguaro is about 13 ft high, and 50 years old that it will develop its first arm. The largest saguaros may be 100-200 years old. Being at the northern end of their range, Arizona saguaros sometimes succumb to cold snaps in the winter months. After death, the saguaro leaves behind a skeleton of wooden ribs.

Cholla Cacti photo © Dave Ingram

The Sonoran desert is home to about 50 species of cacti. Another large cactus, the organ pipe, is found only in Organ Pipe National Monument in the US, though it is common in Mexico. The organ pipe cactus has many branches that rise from the base. Other cacti take on strange and interesting forms, such as the tree-like chain-fruit cholla, which dangles necklace-like chains of fruit from its branches, or the teddy-bear cholla, which glistens in the sunlight with dense yellowish spines. The prickly-pear cactus sports disc-like pads that appear balanced on top of one another. The Javelina, a wild pig, eats these cactus pads spines and all.

Though not a cactus, the spiky ocotillo (oco-tee-yo) was one of my favourite desert plants. Wiry unbranched stems, like pipe cleaners, soar up to nine meters skyward. To conserve water the ocotillo drops its leaves in dry spells, and sprouts new green leaves after it rains.

We sampled the Sonoran desert at Organ Pipe National Monument, and Saguaro National Park on the outskirts of Tucson. Though the cacti were not yet in bloom, we enjoyed many spring flowers. Clumps of Brittlebush, a shrub with yellow daisy-like flowers, turned the hillsides a soft yellow. Brilliant orange poppies coloured the now dry washes, and there where some nice displays of hot-pink owl clover, and white chicory.

The drama of the landscape, the cacti, the flowers, and red rocky hills were set off by a sweep of blue sky. We felt in awe of the landscape, and after a crash course in desert ecology at the Arizona-Sonoran Desert Museum in Tucson, we continued our journey. Read the next article...