Saguaro cactus

Appearance

The saguaro is a columnar cactus that grows notable branches, usually referred to as arms. Over 50 arms may grow on one plant, with one specimen having 78 arms. Saguaros grow from 3–16 m tall, and up to 75 cm in diameter. They are slow growing, and routinely live 150 to 200 years. They are the largest cactus in the United States.

The growth rate of this cactus is strongly dependent on precipitation; saguaros in drier western Arizona grow only half as fast as those in and around Tucson. Saguaros grow slowly from seed, and may be only 6.4 mm tall after two years. Cuttings rarely root, and when they do, they do not go through the juvenile growth phase, which gives a different appearance. Since 2014, the "National Register of Champion Trees" listed the largest known living saguaro in the United States in Maricopa County, Arizona, measuring 13.8 m high with a girth of 3.1 m; it has an estimated age of 200 years and survived damage in the 2005 Cave Creek Complex Fire. The tallest saguaro ever measured was an armless specimen found near Cave Creek, Arizona. It was 78 ft in height before it was toppled in 1986 by a windstorm. Saguaros are stem succulents and can hold large amounts of water; when rain is plentiful and the saguaro is fully hydrated, it can weigh between 1,500 and 2,200 kg.

Saguaros have a very large root network that can extend up to 30 m, and long taproots of up to 1 m deep.

Saguaros may take between 20 and 50 years to reach a height of 1 m. Individual stomatal guard cells and medulla cells can live and function for as long as 150 years, possibly the longest living of all cells, except possibly nerve cells in some tortoises.

As a cactus, it uses crassulacean acid metabolism photosynthesis, which confers high levels of water-use efficiency. This allows the saguaro to transpire only at night, minimizing daytime water loss.

A saguaro without arms is called a "spear".

Some saguaros grow in rare formations called a cristate, or "crested" saguaro. This growth formation is believed to be found in one in roughly 10,000 saguaros, with 2,743 known crested saguaros documented. The crest formation, caused by fasciation, creates a seam of abnormal growth along the top or top of the arm of the saguaro.

Distribution

The Saguaro is endemic to the Sonoran Desert and is found primarily in western Sonora in Mexico, and in western Arizona in the US. There are only 30 known wild saguaros found in southeastern California. Elevation is a limiting factor to its environment, as the saguaro is sensitive to extended frost or cold temperatures. No confirmed specimens of wild saguaros have been found anywhere in Nevada, New Mexico, Texas, Colorado, Utah, nor in the high deserts of northern Arizona. The northern limits of their range are the Hualapai Mountains in Arizona. They are the northernmost columnar cacti in the Americas.: 320

Status

Harming or vandalizing a saguaro in any manner, such as shooting them is illegal by state law in Arizona. When houses or highways are built, special permits must be obtained to move or destroy any saguaro affected. Exceptions to this general understanding exist; for example, a private landowner whose property is 10 acres or less, where the initial construction has already occurred, may remove a saguaro from the property. This is common when the cactus falls over in a storm, its location interferes with a house addition, or it becomes a potential hazard to humans.

In 1982, a man was killed after damaging a saguaro. David Grundman was shooting and poking at a saguaro cactus in an effort to make it fall. An arm of the cactus, weighing 230 kg, fell onto him, crushing him and his car. The trunk of the cactus then also fell on him. The Austin Lounge Lizards wrote the song "Saguaro" about this death.

Contrary to published statements, no law mandates prison sentences of 25 years for cutting a cactus down; however, it is considered a class-four felony with a possible 3-year, 9-month maximum sentence.

Invasive species, such as buffelgrass and Sahara mustard, pose significant threats to the Sonoran Desert ecosystem by increasing the rate of fires. Buffelgrass outcompetes saguaros for water, and grows densely. It is also extremely flammable, but survives fire easily due to deep root systems. Saguaros did not evolve in an environment with frequent fires, thus are not adapted to fire survival. Most Sonoran desert ecosystems have a fire return interval greater than 250 years; buffelgrass thrives at fire return intervals of two to three years. This has led to the reshaping of the Sonoran Desert ecosystem and threatens the survival of the saguaro.

Climate change may threaten saguaros and their ecosystems, as deserts are particularly susceptible to climate effects. Rising daytime and nighttime temperatures will reduce the water use efficiency of saguaros, forcing them to use more water and making them more likely to die during drought periods.

Habitat

The Saguaro is endemic to the Sonoran Desert and is found primarily in western Sonora in Mexico, and in western Arizona in the US. There are only 30 known wild saguaros found in southeastern California. Elevation is a limiting factor to its environment, as the saguaro is sensitive to extended frost or cold temperatures. No confirmed specimens of wild saguaros have been found anywhere in Nevada, New Mexico, Texas, Colorado, Utah, nor in the high deserts of northern Arizona. The northern limits of their range are the Hualapai Mountains in Arizona. They are the northernmost columnar cacti in the Americas.: 320 The saguaro is a keystone species, and provides food, shelter, and protection to hundreds of other species. Every stage of the saguaro's life sustains a significant number of species, from seedling to after its death.

Reproduction

Gila woodpeckers and gilded flickers create holes in the cactus to make nests, which are later used by other birds, such as elf owls, purple martins, and house finches.
Cavities in saguaro cactuses in the Southwest are common. Both gilded flickers and Gila woodpeckers make these cavities for nesting, but they often choose different locations on the cactus. The stouter bills of the gilded flickers allow them to cut cavities through the wooden ribs near the top of the cactus where the ribs converge.
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Gila woodpeckers stay at midlevel on the cactus where the ribs are separated enough to cut a cavity between them. Cavities in saguaros are cut out by these birds the year before they are inhabited. The excavated cactus secretes a fluid that hardens into a scab, thus preventing water loss, which could kill the cactus, as well as waterproofing the inside of the nest cavity. — Elbroch, Marks & Boretos, p. 311 harvp error: no target: CITEREFElbrochMarksBoretos2001
Gilded flickers excavate larger holes higher on the stem compared to Gila woodpeckers. The resulting nest cavity is deep, and the parents and young are entirely hidden from view. The saguaro creates callus tissue on the wound. When the saguaro dies and its soft flesh rots, the callus remains as a so-called saguaro boot, which was used by natives for storage.

Gila woodpeckers create new nest holes each season rather than reuse the old ones, leaving convenient nest holes for other birds, such as elf owls, tyrant flycatchers, and wrens.
Although they do not use them immediately, waiting first for the sap to harden, Gila woodpeckers excavate cavities in cacti and trees as nesting sites. Females typically lay two broods a year of three to five eggs, which incubate for 14 days.
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Once abandoned, the cavities are occupied by reptiles, rodents, and small birds like kestrels, elf owls, flycatchers, and wrens.
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In the desert, the woodpeckers perform the important ecological function of removing unhealthy flesh from the saguaro cactus. Some insects on which it feeds carry diseases, harmless to the bird, which damages the cactus and leaves discolorations. The marks signal larvae to the bird, and as it excavates the insects, it also cuts away the diseased tissue. As the sap hardens, the cactus is healed, and the excavation becomes a convenient nesting site. — Nature Conservancy
In recent years, early-breeding aggressive non-native birds have taken over the nests, to the detriment of elf owls that breed and nest later. In 2020, a bald eagle was found nesting in a saguaro for the first time since 1937.

Food

The saguaro provides voluminous amounts of pollen, nectar, and fruits. The fruits are eaten by the white-winged dove and ants, so that seeds rarely escape to germinate. White-winged doves are important pollinators, visiting blooms more often than any other bird species. For desert white-winged doves, 60% or more of their diet is saguaro-based. Their breeding cycle coincides with that of the saguaro blooming.

Cultural

Arizona made the saguaro blossom its territorial flower on March 13, 1901, and on March 16, 1931, it became the state flower.

The saguaro is often used as an emblem in commercials and logos that attempt to convey a sense of the Southwest. Notably, no naturally occurring saguaros are found within 400 kilometers of El Paso, Texas, but the silhouette is found on the label of Old El Paso brand products. Though the geographic anomaly has lessened in recent years, Western films once enthusiastically placed saguaros in the Monument Valley of Arizona, as well as New Mexico, Utah, and Texas.

America West Airlines, and later U.S. Airways after their merger in 2007, used the call sign "CACTUS" for radio communication on flights. America West was based in Phoenix, AZ, and "cactus" was chosen as a tribute to the saguaro cacti growing in the Phoenix area.