nature

If you are in the mood to see a saguaro cactus, you will have to go to the Sonoran Desert-northwestern Mexico, southern and western Arizona, or a strip along the California side of the Colorado River. The cactus grows nowhere else in the world. Its great size and distinctive form make an adult saguaro easy to spot. Is it the biggest cactus in the world? No it is not, although it is close to the top of the list. Even though few saguaros actually go above 30 feet, they nevertheless seem inordinately tall, perhaps by contrast with the smaller desert plants surrounding them. How do you pronounce its name? The saguaro, which is sometimes spelled "sahuaro," is properly pronounced suh-WARoh. Pronunciation can be a problem for newcomers to the desert, but these giant cactusesmmore than compensate for any trouble their name causes by adding so much drama and majesty to their special environment. Why don't saguaros grow throughout the arid Southwest? The saguaro and other desert plants that define the Sonoran Desert are not adapted to cold weather. If temperatures stay below freezing for more than 24 hours, this cactus is in deep trouble. At higher elevations about an hour's drive north of Phoenix, cactus-killing freezes occur too frequently for saguaros to survive. Even within the low desert, the rare hard freeze, coming at intervals of a decade or more, kills or damages many of them on shaded slopes and in depressions. The occasional freezes in saguaro country contribute to the wonderful individuality of the adult cactuses. Those distinctive saguaros with an undulating arm or two have been hit by a hard frost sometime in the past. Portions of their arms froze, weakening the tissue and causing the appendages to droop downward. If the damaged arms do not die, they eventually begin growing up against gravity once again. Why doesn't the extreme heat of the

EVERYTHING YOU EVER WANTED TO KNOW ABOUT Saguaros

Saguaros

THE REALLY LARGE SAGUAROS, THE 20TO 40-FOOTERS, HAVE WATCHED OVER THE DESERT FOR MORE THAN A CENTURY.

summer kill saguaros? Prolonged heat and drought can kill them. But once a saguaro gets to be a foot or so tall, it possesses a thick waxy skin that helps it avoid rapid water losses even during the hottest, driest part of a Sonoran Desert summer. Water conservation is a key to the survival of the saguaro (and other desert-adapted plants). Most cactuses, the saguaro included, not only have waxy, water-tight surfaces, they also close the microscopic pores in their green chlorophyll-containing skin during the day. Only at night do the pores open to capture the carbon dioxide the cactuses need to make life-sustaining sugars. Because temperatures are reduced at night, water losses from their pores are kept to a minimum. How old are the big saguaros? Cactuses as a group are extremely slowgrowing because their need to conserve water interferes with efficient photosynthesis. A saguaro requires about 25 years just to reach the three-foot mark; another 15 years or so will pass before the cactus is as tall as a man. Not until the plant is 50 or 60 years old will it produce its first flower. The really large attention-getting saguaros, the 20-to 40-footers, have watched over the desert for more than a century, and a few may have been around for 200 years or so. Rainfall or the lack thereof can affect the growth rate of a saguaro so dramatically that a 30-year-old saguaro at Saguaro National Park East will be more than three feet tallerthan a similar-age one at the drier Organ Pipe Cactus National Monument. Why are so many of the big cactuses riddled with holes?

Saguaros

Let us ignore, if we can, the small holes caused by bullets fired by a certain class of "sportsmen" and focus instead on the large dark holes dug into full-size saguaros. These are the handiwork of Gila woodpeckers and gilded flickers, which chop through the thick skin to form nest chambers within the flesh of the cactus. Fresh wounds of this sort can sometimes become infected by a potentially lethal bacterium. But healthy saguaros have the ability to seal off open wounds with dense scar tissue, which quickly surrounds the cavities excavated by the birds. But once constructed, the nests of woodpeckers and gilded flickers are there to stay. After the first year, the chambers serve nesting ash-throated flycatchers and elf owls (and starlings, too, these days).

The old nests of woodpeckers and gilded flickers endure even after the death of the host saguaro. In my favorite saguaro forest, a true giant went down in a monsoon rainstorm in August, 1983. In the years since then, the flesh of this 35-footer has decayed and disappeared, leaving behind a pale skeleton of ribs, the central column of woody tissue that supports the body of the saguaro, and a large number of saguaro "boots," the durable containers of scar tissue that once were filled with baby birds.

Why is the body of the saguaro pleated instead of smooth?

The pleats or ridges running up and down the trunk and arms of the saguaro are part of the plant's water-storage system. Saguaros are wonderfully adept at collecting water and storing it when it is available. In most years, desert rains come at the end of summer and during winter. As soon as a storm replenishes soil moisture, a host of small water-collecting hairs quickly develop all along the extensive shallow root system of the cactus. These "rain roots" absorb water, which is transported to the body of the cactus and stored there.

The saguaro has a skeleton consisting of a cylinder of semi-independent rods (the saguaro's ribs). The ribs surround a pithy central core and are in turn surrounded by a coat of fleshy tissue. The flesh of the cactus takes up water and as the nourished internal cells swell, the pleats permit the body of the cactus to expand without cracking or splitting. As the plant gradually uses its water supply during droughts, its body deflates and the pleats become more pronounced again.

If you cut into a water-swollen saguaro, could you collect water to drink?

In the first place, chopping into a saguaro is an illegal act that could earn you jail time and a $3,000 fine. In the second place, no fluid would flow from the wound, and even if you were somehow able to extract liquid from a quantity of saguaro flesh, you would find it a bitter and poisonous brew. The cells of a saguaro contain chemical toxins that make its flesh and fluids unappealing to most desert plant-eating animals.

When can I see saguaros in bloom?

Typically in late May, when temperatures are already passing the 100° F. mark, tiny green flower buds push through the white cottony patches that protect the growing tissue on arm tips and trunk tops from extremes of heat and cold. The buds grow until they achieve a height of four or five inches and a shape like a light bulb. Then one day the first bud opens into a magnificent creamy-white flower that glows from its elevated perch.

Each flower survives for a day and a night, spreading its white petals around a great army of pollen-bearing anthers. During the day, bees and other insects disappear into the upright anthers as they travel down to the base of the flower for nectar. At night bats plunge face-first into the flowers, licking up nectar and carrying off pollen on their fur to still other flowers.

All through June, flowers open, pollinators come and go, and flowers close in a disorganized jumble of petals. Temperatures climb even higher. At the base of each pollinated flower, a small green fruit begins to expand even as the flower above it wizens into a stiff, black, useless appendage.

As they mature, the fruits grow to the size of a large plum and then turn orange or red before splitting along three or four seams. The thick rind slowly pulls back, revealing the scarlet inner lining of the fruit. The red flag advertises the availability of a core of red pulp riddled with blackish seeds. House finches and white-winged doves hurry in to gather the food, leaving behind only flared, empty rinds, which soon topple from the cactus to lie on the desert floor.

A single saguaro fruit contains as many as 2,000 seeds, and botanists have estimated that a long-lived adult can expect to produce upward of 40 million seeds during its lifetime. The overwhelming majority are immediately harvested and digested by seed-eating birds and rodents. But a few seeds will pass intact through a consumer's gut and fall into crevices between rocks or onto the soil beneath concealing bursages or patches of dried grass.

As June becomes July, more and more fruits mature, split open, are harvested, and more and more seeds find their way to hiding places. By early August, most fruits are eaten, and the adult saguaros have lost their flamboyance for another year.

FOR DECADES, CATTLE REMOVED THE GRASS COVER NEEDED BY SEEDLING SAGUAROS, SO FEW YOUNG SAGUAROS BECAME ESTABLISHED THERE.

Most years the first summer thunderstorms arrive in late July, sweeping the desert clean with their violence. Additional rains provide the soil moisture that stimulates tiny saguaro seeds to germinate in good numbers. A new generation starts the improbable journey to adulthood. It will be a long haul. The young plant is almost ridiculously tiny, and the seedling saguaro grows with excruciating slowness. After an entire year, it might be a tenth of an inch tall. Most seedlings fail to enjoy even a year of micro-growth, falling prey to foraging rodents or dying during a dry spell, a hot spell, or a cold spell.

Are saguaros an endangered species in Arizona?

Despite the huge odds against any one seed producing a saguaro that will reach maturity, saguaros are an abundant cactus in some parts of Arizona. Still, conservationists are concerned about the welfare of the species, which has suffered from urban development, overgrazing, illegal poaching of specimens for sale, and weekend target shooters. Even the wonderful forest of fully protected saguaros in Saguaro National Park near Tucson is in severe decline. By the year 2000, there may well be no large adults in much of the eastern part of the park.

This sad state of affairs appears to stem from the long history of cattle grazing in the area, which only ended in the 1970s. For decades, cattle removed the grass cover needed by seedling saguaros, so few young saguaros became established there. As the older cactuses went down from disease, windstorms, and freezes, they were not replaced.

Happily, with the removal of cattle from the parkland, new recruits have become established in droves in recent years, although it will be many more years before the once-impressive forest of giants has formed again. This is particularly true if, as some people fear, air pollution harms the saguaros or if populations of the important bat pollinators continue to decline.

Despite all the past and future problems facing this magnificent cactus, there are still many places in the state where the saguaro is more than holding its own. Its capacity to endure gives cause for celebration, for it is huge yet graceful, tough yet serene, a worthy symbol of life's triumph even in the desert.