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|Saguaro National Park|
One of America's newer national parks is located in the Sonora Desert in southern Arizona approximately 60 miles north of the Mexican border. Saguaro National Park, previously Saguaro National Monument, consists of 91,327 acres which contain spectacular examples of Sonoran Desert ecosystem including a wide variety of desert plants, and of course the famous saguaro cactus, symbol of the American Southwest.
The park is composed of two separate sections--Saguaro East, also known as the Rincon Mountain District (the entrance to which is shown above), and Saguaro West, also known as the Tucson Mountain District--which lie on the opposite side of the city of Tucson. A portion of the eastern section, with the Rincon Mountains in the background, is shown below.
There is evidence of human habitation in the Saguaro area as long ago as 12,000 years ago. The area was much wetter then than it is presently, supporting habitation by animals like the mammoth, bison, and other mammals. About 2300 years ago the Hohokam people settled in the area, and by 700 AD they had learned to practice agriculture. The Hohokam flourished in the Santa Cruz Valley (where Tucson is currently located) for many centuries but vanished in the 15th century.
The Europeans first visited the area in 1694, represented by Spanish Jesuit missionary Padre Eusebio Kenio. He encountered the Tohono O'odham people who practiced a lifestyle based on cultivation and hunting.
From 1821 to 1854 the area was ruled by Mexico. It was used by farmers, miners, merchants, and ranchers. The area became part of the United States in 1854, and after the Civil War and the cessation of Apache raids in the area there was a great increase in the local population. The arrival of the Southern Pacific Railroad in 1879 brought more people. Between 1870 and 1890 there was also a tremendous increase in the use of area for cattle grazing, an activity which had seriously deleterious effects of the growth and survival of young cactus.
In 1933 the Rincon Mountain District was made the Saguaro National Monument. It was the first national park or monument set aside to protect a species of plant. However, in 1959 additional effort was required to resist opening part of the park's area to exploration for copper. In 1961 the 15,360 acres of the Tucson Mountain district were added to the monument by President John F. Kennedy. 21,000 additional acres were later added to this district. The monument was finally made the nation's 52nd national park in a bill signed by President Bill Clinton in October, 1994.
If there is one image most people think of when the desert is mentioned it is the magnificent saguaro cactus.While this image may be synonymous with the desert in actuality the saguaro is endemic to the Sonora Desert. But there are saguaros aplenty in this national park, which in fact represents the extreme northern portion of the saguaro's range. The saguaro lives in dry conditions at altitudes ranging from sea level to about 4500 feet. As such, the conditions in the Tucson basin are ideal for the Saguaro. One of these cactus can be seen below, with a prickly pear cactus in the foreground.
The saguaro grows extremely slowly at the beginning of its life. In fact, it may take 5 years for the young plant to achieve a height of 5 inches! At its fastest, however, the saguaro may grow 5 feet per year.
These cactus are familiar because of their wildly branching arms, but it is not until they're about 65 years old that these arms begin to develop.
Some saguaro develop as many as 50 or more of these appendages.
The saguaro likes the rocky, gravelly soil of the desert. It also requires warm conditions and will die if the temperature does not rise above freezing for any extended period, for example beyond 24 hours. As a result, few can be found above 5000 feet here or elsewhere. In the eastern part of the park the saguaro used grow in a relatively thick forest, but years of grazing by cattle resulted in a serious decline in the numbers and densities of these giants. In fact, even after initial creation of the national monument in 1933 cattle were allowed to continue to graze on the lands among the saguaro. The last feral cattle were not removed from the monument until the mid-1980's.
The saguaro were also seriously affected by some freezing conditions. In February of 1939 temperatures in the area plunged to 25 degrees and remained at that level for several hours. As a result the stands of cactus seen in the eastern section of the park are much less dense than would have been seen years ago. However, in the western section relatively dense stands of cactus may still be seen, and as a result of conservation measures enacted after the area was declared a national monument the saguaro numbers are once again on the rise in the east side.
The saguaro is host to a wide variety of desert life. Gila woodpeckers or gilded flickers bore holes into the cactus, as can be seen below. Because of the high moisture content of the inside of the cactus these holes are well insulated and make an excellent home for several types of animals. In fact, the temperature and microenvironment within a hole is equivalent to what would be found climbing 200 feet up into the mountains.
The cactus is supported by 12-30 internal woody ribs. These can only be seen when the cactus has died and the plant's flesh has decomposed, as in the picture below.
Another shot of a skeletal cactus can be seen below, still standing and serving as a perch for a couple of birds. Typically the mature saguaro lives for a very long time, but it is usually finally felled by lightning, windfall, or extended freezing temperatures.
Another saguaro skeleton can be seen here.
The mature saguaro produces a colorful bloom, which is the Arizona state flower, and which eventually develops into a red fruit.
These fruit are food for many animals and were also gathered by the Indian inhabitants of the area who knocked them off the top of the cactus with long poles.
The saguaro survives through its capacity to store massive amounts of waters. This water is gathered by a shallow, broad root system (ranging up to 50 feet in all directions but never sinking more than three feet into the ground) which takes advatanges of the summer and winter rains which visit this area of the Sonora Desert. The saguaro cactus can soak up to 200 gallons of water when it is available and it can make this supply last for a year. The water is stored in the cactus's soft internal tissues and it expands and contracts like an accordion as its supply of stored water supply varies. Its waxy coating also helps keep retard moisture loss through evaporation.
Although each saguaro produces millions of seeds, only a very small number of small plants may survive. The year old saguaro may be only a few inches high. Often, a palo verde tree which provides shade and other forms of protection functions as a "nurse" for the young cactus.
The saguaro is a magnificent plant by any estimation. It can be up to 50 feet high (they average about 35 feet at maturity) with branches beginning some 12 feet above the ground, has a diameter of about 30", may weigh over 5 tons (as much as 90% of which is water), and it may live for 200 years, although few live more than 150.
Although development in southern Arizona poses a serious threat to its range, preservation of some of the best stands within the national park boundaries greatly increases its chances for survival.
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