May 6, 2001
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Site Highlights:
Near Tucson
Uncrowded
Desert ecology trail
Hiking trails
Cactus forest drive
Picnic grounds
A desert museum
| Go to first part of trip - Colossal Cave Go to third part of trip - San Xavier Mission Go to fourth part of trip - Pima Air & Space Museum |
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Route To Site
Site Map of Saguaro National Park
Site Map of Saguaro National Park (East)
Panoramic View of Saguaro National Park
The Saguaro
Site Gallery - At Saguaro National Park
The life of a saguaro
Storing and conserving water
Site Gallery - The Saguaro
Saguaro flowers
Site Gallery - The Saguaro Flower
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| The Saguaro The Monarch of the Southwest |
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The saguaro has been described as the monarch of the Sonoran Desert, as a prickly horror, as the supreme symbol of the American Southwest, and as a plant with personality. It is renowned for the variety of odd, all-too-human shapes it assumes, shapes that inspire wild and fanciful imaginings.
In lushness and variety of life, the Sonoran Desert far surpasses all other North American deserts. And yet, it is one of the hottest and driest regions on the continent. Summer midday temperatures commonly climb above 100 degrees. Fewer than 12 inches of rain falls in a typical year. The plants and animals able to survive in this environment, with adaptations specially designed for desert survival, make up one of the most interesting and unusual collections of life in the United States. |
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| Site Gallery - At Saguaro national Park |
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| The life of a Saguaro |
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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 its life, 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 Green 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. By the end of a year the saguaro seedling may measure only 1/4 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 and weighing 8 tons, sometimes more, dwarfing every other living thing in the desert. These are the largest cacti in the United States. A strong but flexible cylinder-shaped framework of long woody ribs supports their huge bulk. 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 deaths have greatly outnumbered the growth of new young saguaros in some forests within the park. What has caused the decline in these areas? Biologists believe that severe 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. |
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| Storing and conserving water |
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Many features assist the saguaro in storing and conserving the 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 that transpire large amounts of water. The food-making process of photosynthesis narmally carried out by green leaves is performed in the trunk and branches. Spines discourage animals from taking the cactus's moisture, shade the plant, and shield it from drying winds. Waxy skin aids in reducing moisture loss. | ||
| Site Gallery - The Saguaro |
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| The saguaro flower |
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Saguaro flowers -- big, bold, and numerous -- bloom and color the desert in late April, May, and June. Each blossom opens in the cool of the night a few hours after the sunset. By the next afternoon, the flower has wilted and the brief period of bloom has ended. The spectacle repeats itself night after night for about four weeks until as many as one hundred flowers have appeared on each saguaro. | |
| In the few hours the flowers are open a variety of flying animals will have succeeded in poliinating many of them. Whitewinged doves and long nose bats -- summer migrants from Mexico --- honey-bees, 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.
In June and July the fruit of the saguaro ripens. The sugary pulp of each fruit contains as many as 2,000 seeds. Javelinas, coyotes, foxes, squirrels and other rodents, harvester ants, and many birds feast on the fruit and seeds. |
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| Site Gallery - The Saguaro Flower |
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