Facts About Saguaros

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Saguaro Distribution Life of a Saguaro Features of the Saguaro How the Saguaro Collects Water	The Saguaro's Flowers, Fruits, and Seeds The Saguaro as a Home People's Use of the Saguaro Saguaro Cacti Stats

Saguaro Distribution

Saguaro cacti, Carnegiea gigantea, only grow in the Sonoran Desert. However, they do not grow in all parts of the Sonoran Desert. The map on the right represents the range of the Sonoran Desert (crosshatch) with an overlay of the range of the saguaro cactus (solid). The range of the saguaro is limited by freezing temperatures in winter.

Saguaros are also limited by elevation. They are generally found growing from sea level to approximately 4,000 feet in elevation. Saguaros growing higher than 4,000 feet are usually found on south facing slopes where freezing temperatures are less likely to occur or are shorter in duration.

[Large Map]

Life of a Saguaro

The Struggle for Survival Begins

The saguaro begins its life as a shiny black seed no bigger than a pinhead. But what it lacks in size it more than makes up for in numbers. One saguaro produces tens of thousands of seeds in a year, and as many as 40 million in a lifetime of 175 to 200 years.

From the start, the odds against survival are great. Out of all the seeds that a saguaro produces in a lifetime, few will survive to adulthood.

Seeds and young saguaros have the best chance for survival if they are cared for by nurse trees such as palo verde and mesquite. Saguaro seedlings that grow under these sheltering plants are shaded from the desert's intense sunlight, blanketed from winter cold, and hidden from rodents, birds, and other animals that eat them. Rocks provide similar protection for young saguaros. Saguaros do best on bajadas–gently sloping outwash plains at the foot of desert mountains.

Growth of a Giant

A saguaro's growth is extremely slow. Growth occurs in spurts, with most of it taking place in the summer rainy season each year. The growth rate varies slightly depending on factors such as the annual rainfall of the area. The eastern Sonoran desert around Saguaro National Park receives more rainfall than that of western Arizona, and so the growth rate tends to be higher. By the end of a year the saguaro seedling may measure only ¼ inch. After 15 years, the saguaro may be barely a foot tall. At about 30 years saguaros begin to flower and produce fruit. By 50 years the saguaro can be as tall as 7 feet. After about 75 years it may sprout its first branches, or "arms". The branches begin as prickly balls, then extend out and upward.

By 100 years the saguaro may have reached 25 feet. Saguaros that live 150 years or more attain the grandest sizes, towering as high as 50 feet or more and weighing 10 tons, sometimes more, dwarfing every other living thing in the desert. These are the largest cacti in the United States. Their huge bulk is supported by a strong but flexible cylinder-shaped framework of long woody ribs.

Death and Rebirth

Saguaros may die of old age, but they also die of other causes. Animals eat the seeds and seedlings, lightning and winds kill large saguaros, and severe droughts weaken and kill all ages. The saguaro is vulnerable during every stage of its life.

Where there is a balance of life and death, saguaro forests thrive. Until recent years, in some forests in the park, deaths have greatly outnumbered the growth of new young saguaros. What has caused the decline in these areas?

Biologists believe killing freezes are the park's major cause of saguaro deaths. The saguaros here are at their extreme northern and eastern range, where the coldest winter temperatures most often occur. Humans, too, have played a part in the decline. Livestock grazing, which continued from the 1880s until 1979, devastated some cactus forests. Seedlings were killed outright by trampling or were unable to find suitable places to grow because the ground had been compacted and nurse plants killed.

Today, with grazing eliminated, recovery of the saguaro is underway in several areas. Thousands of young saguaros have taken hold, and they are thriving. Still, natural forces, vandalism, and cactus rustling – the theft of saguaros for use in landscaping – continue to take a toll on the park's saguaro forests.

Features of the Saguaro

Many features assist the saguaro in storing and conserving that most precious of desert commodities – water. Accordion-like pleats allow the saguaro to expand and hold water collected through the roots. Spongy flesh in the trunk and branches serves as a reservoir where water is stored as a slow-to-evaporate gelatin-like substance. Unlike most plants, the saguaro cactus has no conventional leaves, which transpire large amounts of water. The food-making process of photosynthesis normally carried out by green leaves is performed in the trunk and branches. Spines discourage animals from taking the cactus' moisture, shade the plant, and shield it from drying winds. Waxy skin aids in reducing moisture loss.

Saguaro Pleats

The roots of a saguaro grow out from the plant in a radial fashion, several inches under the ground. During a heavy rain, a saguaro will absorb as much water as its root system allows.

To accomodate this potentially large influx of water, the pleats expand like an accordion. Conversely, when the desert is dry, the saguaro uses its stored water and the pleats contract.

Because the majority of a saguaro is made up of water, an adult plant may weigh 6 tons or more. This tremendous weight is supported by a circular skeleton of inter-connected, woody ribs.

The number of ribs inside the plant correspond to the number of pleats on the outside of the plant. As the saguaro grows, the ribs will occasionally fork and the corresponding pleat will also fork at the same place.

Why Some Saguaros are Crested

Even when saguaro cacti grow in their normal form, they rarely grow symmetrically. Saguaros sometimes grow in odd or mis-shapen forms. The growing tip occasionally produces a fanlike form which is referred to as crested or cristate.

Though these crested saguaros are somewhat rare, over 25 live within the boundaries of the park. Biologists disagree as to why some saguaros grow in this unusual form. Some speculate that it is a genetic mutation. Others say it is the result of a lightning strike or freeze damage. At this point we simply do not know what causes this rare, crested form.

How the Saguaro Collects Water

The saguaro collects water with a network of roots that lies about 3 inches below the surface and stretches as far out from the main stem as the saguaro is tall. In a single rainfall, these shallow roots–along with special small root hairs that grow moisture–may soak up as much as 200 gallons of water, enough to last the saguaro a year.

The Saguaro's Flowers, Fruit, and Seeds

The saguaro flower forms a cluster of creamy white petals around a dense group of yellow stamens on a 4 inch long stem. The saguaro has more stamens per flower than any other cactus flower.

Pollination

In the few hours the flowers are open a variety of flying animals will have succeeded in pollinating many of them. Whitewinged doves and longnose bats–summer migrants from Mexico–honeybees, and moths accidentally become powdered with sticky pollen as they feed on the sweet nectar inside the flower. As they travel from flower to flower, they transport the pollen, fertilizing as they go. A saguaro can only be fertilized by pollen from another cactus. If fertilization has taken place, a fruit will begin to form at the base of the flower.

Fruit

In June and July the fruit of the saguaro ripens. The sugary pulp of each fruit can contain more than 2,200 seeds. Javelinas, coyotes, foxes, squirrels and other rodents, harvester ants, and many birds feast on the fruit and seeds.

The Saguaro as a Home

The saguaro is like a multi-storied apartment complex: many animals live in close quarters and the occupants change constantly. Two common residents are the Gila woodpecker and gilded flicker. These birds dwell in nest holes they make in the trunk and larger branches of saguaros. The birds excavate new holes each spring, and they often make and reject several cavities in one nesting season before settling in one and raising a family. Their industriousness leaves many holes for other animals, who rapidly move in. The birds who compete for the homes include American kestrel, Lucy's warblers, cactus wrens, western kingbirds, phainopeplas, elf owls, and purple martins. Honeybees also inhabit some holes. For residents, the holes are a retreat from desert temperature extremes. Well insulated by thick walls, the holes are as much as 20º F cooler in the summer and 20º F warmer in the winter than outside. Other saguaro dwellers live not in holes but in bulky nests. These include red-tailed hawks and Harris' hawks.

Learn more about the animals of Saguaro National Park on our Animals page.

People's Use of the Saguaro

For centuries peoples of the Sonoran Desert have used natural products of the saguaro. In the summer the saguaro provided a nourishing bounty of juicy, fig-like fruits. Native Tohono O'Odham Indians harvested them by knocking them off the tall cacti with long poles. From the fresh fruit the Tohono O'Odhams made jam, syrup, and, for their religious ceremonies, wine. So important was the fruit to the Tohono O'Odhams that the season of harvest marked the beginning of their new year. The saguaros also provided seeds for the Tohono O'Odhams and their chickens to eat, and strong woody ribs, which the plant uses to support its huge weight, to build shelters and fences.

Saguaro Cacti Stats Classification Kingdom    Subkingdom    Superdivision Division Class    Subclass Order Family    Cactus Group Genus Species Plantae    Tracheobionta    Spermatophyta Magnoliophyta Magnoliopsida    Caryophyllidae Caryophyllales Cactaceae    Cereus Carnegiea Carnegiea gigantea Plants Vascular plants Seed plants Flowering plants Dicotyledons Cactus Saguaro Location Location Range Westernmost Northwesternmost Easternmost Southernmost Elevation Habitat Soil Densest Forest Sonoran Desert (map) S AZ, Sonora, SE CA (3 isolated sparse sites along the Colorado) (map) Colorado River Hualapai Mountains, near Kingman, AZ Galiuro Mountains, NE of Tucson, AZ Rio Mayo, Sonora 0' - 4500' Desert, esp. sloping foothill bajadas, relatively frost-free areas Coarse, gravely, airy, good drainage Saguaro NP, Tucson Mtn. District Life Cycle Seed            2-3    days 6  weeks >6  weeks 1     year 7   years 10   years 15   years 20   years 25   years 30   years 40   years 50   years 75   years 100   years 125   years 150   years 200+ years Small pinhead-size Germination Av. life expectancy - new saguaros (critical period) <1% live longer ¼" high Woody ribs appear 1½" - 3" high 9" high 18" high 26" high Flowers and fruit 7'+ high 12'+ high Arms begin to grow 30'+ high 36'+ high 41'+ high Lifespan Size Weight Height Record Height Seed/Maturity Ratio Trunk Width 10 tons + 50' + 78' (died in 1986) 100's of millions 3' + Root System Depth Length Water intake 3" below the surface 50'+ from the main stem 200 gallons absorbed during a single rainfall Flowers Size Stem Color Annual production Bloom period - Species Bloom period - Individual saguaro Bloom period - Individual flower Bloom cycle - Individual flower 3" wide 4" long Creamy white 100 Late April - June 4 weeks 1 day Late night until next afternoon Fruit Color Ripens Food Deep red Late June and July Fruit, syrup, juice, jam Seeds Color Single fruit production Annual production Lifetime production Survival rate Germination rate Glossy, reddish-black 2,200+ Tens of thousands 40,000,000 Only a few of all of these will survive until adulthood <1 in 1,000 Ribs No. of ribs - young saguaro No. of ribs - adult saguaro No. of ribs - saguaro arms 10 - 13 20 - 30 15+ Animal Use Animal use Animal hole insulation Nest dwellers Hole makers Other occupants Pollinators Eaters – fruit & seed Food, home, shelter, shade, safety Summer: 20º cooler / Winter: 20º warmer Red-tailed hawks, Harris' hawks, etc. Gila woodpecker, gilded flicker, etc. American kestrel, Lucy's warblers, cactus wrens, western kingbirds, phainopeplas, elf owls, purple martins, bats, bees, insects, etc. Whitewinged doves, longnose bats, bees, moths, etc. Javelinas, coyotes, foxes, squirrels, rodents, harvester ants, many birds, etc. Miscellaneous Pronunciation Color Tissue U.S. cacti size rank Cristate saguaros More moisture = Status Saguaros in Park (sah-WAH-row) Light olive green May be 85% water 1 1 in 250,000 (25+ in park) More saguaro arms Protected; AZ State Flower; Park symbol 1.6 million

Related Topics:   Science • Climate • Animals • Geology • Deserts • Geography • Riparian Areas • Biotic Communities • Sky Islands • Plants

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