The Saguaro Cactus

The Saguaro Cactus Where do saguaros grow? Saguaro cacti, Carnegiea gigantea, only Saguaros are also limited by elevation. grow in the Sonoran Desert. However, They are generally found growing from they do not grow in all parts of the sea level to approximately 4,000 feet Sonoran Desert. The map at left repre- in elevation. Saguaros growing higher sents the range of the Sonoran Desert than 4,000 feet are usually found on (crosshatch) with an overlay of the south facing slopes where freezing tem- range of the saguaro cactus (solid). The peratures are less likely to occur or are range of the saguaro is limited by freez- shorter in duration. ing temperatures in winter. How do saguaros grow? Saguaros are a very slow growing cac- Here at Saguaro National Park, branch- tus. In Saguaro National Park, studies es normally begin to appear when a indicate that a saguaro grows between saguaro reaches 50 to 70 years of age. In 1 and 1.5 inches in the first eight years of areas of lower precipitation, it may take its life. up to 100 years before arms appear. These tiny, young saguaros are very When a saguaro reaches 35 years of age hard to find as they grow under the it begins to produce flowers. Though protection of a “nurse tree”, most often normally found at the terminal end of a palo verde, ironwood or mesquite the main trunk and arms, flowers may tree. As the saguaro continues to grow, also occur down the sides of the plant. its much older nurse tree may die. Flowers will continue to be produced Some scientists believe that competi- throughout a saguaro’s lifetime. tion from the saguaro may lead to the death of the nurse tree by taking water An adult saguaro is generally consid- and nutrients from the soil in the im- ered to be about 125 years of age. It may mediate area. weigh 6 tons or more and be as tall as 50 feet. The average life span of a saguaro As a saguaro begins to age, growth is probably 150 - 175 years of age. How- rates vary depending on climate, pre- ever, biologists believe that some plants cipitation and location. We do know may live over 200 years. that the period of greatest growth in a saguaro cactus is from unbranched to branched adult. Why are saguaros pleat- The roots of a saguaro grow out from made up of water, an adult plant may ed? the plant in a radial fashion, several weigh 6 tons or more. This tremendous inches under the ground. During a weight is supported by a circular skel- heavy rain, a saguaro will absorb as eton of inter-connected, woody ribs. much water as its root system allows. The number of ribs inside the plant correspond to the number of pleats on To accomodate this potentially large in- the outside of the plant. As the saguaro flux of water, the pleats expand like an grows, the ribs will occasionally fork accordion. Conversely, when the desert and the corresponding pleat will also is dry, the saguaro uses its stored water fork at the same place. and the pleats contract. Because the majority of a saguaro is Why are some saguaros Even when saguaro cacti grow in their over 25 live within the boundaries of crested? normal form, they rarely grow sym- the park. Biologists disagree as to why metrically. Saguaros sometimes grow some saguaros grow in this unusual in odd or mis-shapen forms. The grow- form. Some speculate that it is a genetic ing tip occasionally produces a fan-like mutation. Others say it is the result of form which is referred to as crested or a lightning strike or freeze damage. At cristate. Though these crested saguaros this point we simply do not know what are somewhat rare, causes this rare, crested form. Do animals use the sa- Saguaro cacti are host to a great vari- abandoned hawk nest. guaro? ety of animals. The gilded flicker and Saguaro cacti also provide a valuable Gila woodpecker excavate nest cavities source of food for animals. In late sum- inside the saguaro’s pulpy flesh. When mer, ripening fruit provides moisture a woodpecker abandons a cavity, elf and an energy-rich food during a time owls, screech owls, purple martins, of scarcity. finches and sparrows may move in. In drier areas of the Sonoran Desert, Large birds, like the Harris’s and red- pack rats, jackrabbits, mule deer and tailed hawks, also use the saguaro for bighorn sheep will also eat the saguaro’s nesting and hunting platforms. Their flesh when other water sources are not Gila Woodpecker stick nests are constructed among the available. arms of a large saguaro. In turn, ravens and great horned owls may take over an How does the saguaro In late April through early June, the system unharmed and are distributed reproduce? tops of the saguaro’s trunk and arms throughout the desert. However, if the sprout a profusion of large, creamy seeds are eaten by a dove or quail, they white flowers. Individual flowers open will be completely consumed in the at night and close the following after- digestive system. noon. To develop into fruits, they must be pollinated within this time frame. It is estimated that a saguaro can pro- Pollination is carried out by nectar duce some 40 million seeds during its feeding bats, birds and insects. lifetime. However, few will survive to become a seedling. Fewer still will be- Each fruit contains about 2,000 tiny come an adult. The low survival rate of Lesser Long-nosed Bat black seeds. When the fruit and seeds seedlings is due to drought, prolonged are eaten by a coyote or cactus wren, freezing and animals eating them. the seeds pass through their digestive Do humans use the sa- Archeological evidence indicates that These long poles were used to knock guaro? the Hohokam used the saguaro in their ripe fruit down from the top of the daily life. The strong, woody ribs were plants. It would then be gathered to eat. gathered to construct the framework for the walls of their homes. The Tohono O’odham continue to gath- er saguaro fruit in this manner. They Additionally, saguaro ribs were used to use the sweet fruits to make ceremonial collect saguaro fruits, which grow high wine, jelly and candies. They also use up on the plant. Several ribs were tied the seeds as chicken feed. together with a cross piece at the end. Are there threats to the Reports of a saguaro “disease”, popu- of new homes in the Tucson area has saguaro? larized almost fifty years ago, persist, resulted in a tremendous loss of saguaro but saguaros are not subject to blights. habitat. With this influx of people has The saguaro is a long-lived cactus, most come another threat to the saguaro-ex- affected by long-term climate cycles otic plants. Exotic plants almost always of frost and drought. In actuality, the out-compete native plants for the lim- saguaro is a common plant in the Sono- ited resources of water and nutrients. ran Desert, not an endangered species. They have also led to an increase in wildfires, which harm or kill native veg- Without question, the biggest threat to etation, including the saguaro. the saguaro is our rapidly expanding human population. The development EXPERIENCE YOUR AMERICA.

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