Imagine a modern growing city of more than 800,000 people where a half hour drive lands you in a national park. That’s Tucson Arizona. The park in question is the Saguaro National Park and its two parts are east and west of the city. This nearness to a large urban area is quite unusual in our national park system. Most national parks are located far from population centers and involve spectacular geological features. Saguaro National Park has no unusual canyons or geysers, but features a giant cactus, the saguaro (pronounced sah-WAH-ro).

Tucson is in southeastern Arizona sitting among mountains in the valley of the Santa Cruz River. Don’t expect to catch any fish in the river because it is dry for most of the year. Tucson experiences less than twelve inches of rain annually and summer daytime temperatures regularly are above one hundred degrees Fahrenheit. It is located in a desert, the Sonoran Desert, to be exact. Southern Arizona borders the Mexican state of Sonora which is mostly desert and the region around Tucson is part of it. Most months are totally dry and the rain that falls comes during brief summer and winter rainy seasons.

Given the heat and dryness of the Sonoran Desert, there are amazing communities of adapted plants and animals living there. The saguaro cactus is the largest and most impressive plant able to survive in this desert. The tallest and oldest specimens may reach fifty or more feet. With their arm-like branches, saguaros very often take on a human-like appearance. In the minds of many people, a picture of a saguaro is a symbol which means desert anywhere in the U.S., even though they only grow in this particular place.

The saguaro has a combination of features that make it possible to survive under conditions of low rainfall and high heat. Its root system radiates out in all directions as much as fifty feet in mature plants. Some 95% of the roots lie within a few inches of the surface and very few of the roots go deeper than three feet. Rainfall in the desert comes hard and fast, when it does come, and it barely penetrates the baked soil surface before running off. With its roots so close to the surface, the saguaro is able to take advantage of these desert conditions and soak up enough water in a matter of days, to last a year. In order to deal with so much suddenly available water, the plant must be able to expand its girth to store it. The plant can do this without bursting because an outer skin of accordion-like pleats covers it.

Once the water is inside the plant, it is lost very slowly because the outer skin is waxy and there are no leaves. Most plants pass water into the air through their leaves and in non-desert situations of plentiful rainfall such transpiration is normal and not a problem. In the desert, plants cope with the lack of precipitation and conserve water by having either tiny leaves, losing their leaves for part of the year, or having no leaves at all like the saguaro and its cactus relatives. So, how does a plant make food for itself without green leaves? In the case of the saguaro, the main stems and branches are green with chlorophyll and there they slowly carry on photosynthesis.

The accordion-like pleats add some rigidity to the plant, but the main support is inside the branches and main stem. From bottom to top and out to the tips of the branches, there are woody ribs acting as a kind of skeleton. There may be from twelve to thirty such ribs, which are visible only in dead saguaros where the flesh has rotted away. Sharp spines along the outside folds cover the pleated skin. These serve to provide some shade for the outer skin and keep thirsty animals from eating the plant.

In spite of the formidable covering of spines there are creatures making their homes in or on the saguaro. The Gila woodpecker and gilded flicker live in nest holes they make in the trunk and branches of the plant. They may make and try a few holes before finding one they like and settling down to lay their eggs. Empty holes are quickly filled by a variety of other birds including elf owls and screech owls. Sometimes even bees move into the empty holes. Harris hawks and red-tailed hawks build more conventional nests on the outside. All together about eleven species of birds can find homes in or on the saguaro. No wonder some people think of these giants as apartment houses for birds.

Humans, mainly the native - American Tohono O’Odham people of southern Arizona, also depend on the saguaro. They use the wooden ribs to build shelters and fences, but for them there is something more important that the cactus provides. Starting in April and ending in June, the saguaro sprouts flowers at the tips of trunks and branches. Each flower produces a sweet pulpy fig-like fruit through the June and July ripening period. The Tohono O’Odham harvest the fruits using long poles to knock them loose. They eat the fresh fruit, make preserves and also ferment it into wine for their June New Year celebrations. They may also make a kind of food spread from the hundreds of tiny seeds in each fruit.

In the lifetime of a saguaro, it can produce as many as forty million pinhead size seeds. The fallen ripe fruits are part of the diets of foxes, javelinas, squirrels, coyotes, small rodents and birds. Those seeds that are able to germinate have their best chance of survival if they end up near so-called nurse trees like mesquite or palo verde. Here the young seedlings will be protected from winter cold and summer heat. They may also be hidden from birds and rodents that eat saguaro seedlings as part of their diet.

Growth is slow and the seedlings that survive may only reach about 1/4 inch after the first year. Once established, the saguaro grows about a fraction of an inch taller each year. Thus, a three-foot high plant may be about thirty years old, a seven- foot plant may take fifty years to reach that size and the first branches show up only after about seventy years. The tallest plants are the oldest with those twenty - five feet tall estimated at one hundred years of age. Some of the tallest saguaros are estimated to be as old as two hundred or more years. Within U.S. borders, the saguaro is the largest cactus, but in North America there is one that is even larger. The cardon cactus of Baja California in Mexico has some huge individual specimens over seventy feet high and that species holds the record for producing the tallest cacti in the world.

The people of Arizona early recognized the special character of the saguaro. It has been a protected species since 1933 and its blossom was adopted by the legislature as the state flower of Arizona.