 One tree lives longer. One other tree has a greater diameter. Three other species grow taller. But in volume of total wood, the giant sequoia stands alone. The largest tree and the largest living thing on the face of the earth. The ancestors of the giant sequoia ranged over the northern hemisphere. In the age of dinosaurs, large flying reptiles may have soared over sequoian forests. But as climates changed, as the earth's crust rose and fell in the slow dance of geologic history, the giants retreated. Now the big tree's natural range is restricted to the western slope of the Sierra Nevada in California, a strip 260 miles long, less than 15 miles wide. Only here, in isolated groves, is a sequoia able to reseed and regenerate itself by natural means. The Indians of the central Sierra pondered the size of the giant sequoia and held it sacred. With discovery of the tree by Western man in the middle of the last century, however, it faced unfamiliar kinds of threats. Loggers rushed to the sequoia groves, their eyes popping. But the brittle wood was a scant economic value for more than shingles and grape stakes. The tree's power to move the emotions, even of those who had exploited, led early to its protection in federal and state preserves. When Yosemite Valley and the Mariposa giant sequoia grove was set aside in 1864, the park concept was born in the United States. Excess human curiosity and affection for the big tree, however, presented a threat from trampling its young and damaging its fragile turf. There was a threat of fire, not too much, but too little fire. For millions of years, lightning set fires have been part of the life cycle of sequoian forests. Heat is a rival of the tree. The sequoia has evolved in ways that help it resist the heat of its marriage to fire. Trees only a few hundred years old are wrapped in porous bark up to half a foot thick. The spongy fiber contains little or no resin to fuel flames. It also protects the tree's life-sustaining wood tissues from excess heat. These tissues conduct water and minerals up to the treetop and return food down to the roots. The mature sequoia's crown of evergreen foliage stands so high in the sky that ground fires seldom reach it. Older trees bear the scars of many fires. With most of their hotwood burned away, some of the old giants still produce cones and seeds at a rate approaching that of a 300-year-old youngster. The mature sequoia is ever having died from disease or insect attack. Affliction's common to other trees in their old age. It comes to the giant by toppling. After hundreds or thousands of years of vigorous growth, they suddenly fall, brought down by a storm, by erosion around their shallow root system, or by some other combination of forces. Though it lives long and remains virile throughout its life, the giant sequoia is a classic example of reproductive fragility in the plant world. Most other trees are showering the forest with seeds two years after their cones appear. Sequoia cones stay green and closed on the tree for more than 20 years. Propagation of the giant sequoia is totally dependent on seeds, although its cousin, the coast redwood, is noted for stump sprouting. Many other trees sprout from their roots. Most other species have some kind of seed dormancy, a delaying device that permits seed germination and conditions favor growth. The giant sequoia has no such mechanism. And while the seedlings of competitive trees thrive in a shade, giant sequoia seedlings need sunlight. Even in soil prepared by fire, the sequoia seedling death rate is high. Lack of moisture, insect attack, fungus disease, too much shade, or too much direct sun, each contributes to the mortality of the seedlings. To balance the vulnerability of its young and the scale of species survival, the giant sequoia produces cones and seeds at a prodigious rate. In an average year, a mature tree produces more than 2,000 cones containing nearly half a million seeds. The sequoia also has evolved to serotonous cone. The green, closed cone that stays in the tree for as long as 20 years. By the end of their second year, the cones contain seeds ready for germination. Thousands of cones accumulate on the tree. When fire comes along to dry them out and clean out the groves, an explosive seed release occurs under conditions that favor sequoia reproduction. Continuous year-around seed release is another of the giant sequoia's survival strategies, a strategy based largely on the feeding habits of two animals. The Douglas squirrel, or chicory, a hot spark of life, in John Muir's phrase, feeds on green sequoia cones, much as people chew kernels from an ear of corn. It also cuts and stores cones for eating later. Hundreds of seeds may be found in the piles of chewed cones the chicory's leave in sequoia groves. Also important to survival of the sequoia is a tiny cone-boring beetle. The beetle larvae chew their way into the cone's interior, taking nourishment from its tissues. As cone veins are cut, the scales dry out and shrink. Permitting seed fallout over a period of months as the beetle eats its way through. The chicory and the beetle feed mostly on cones of different ages and thus complement each other as seed release devices. Each of the seeds, small as a grain of wheat, holds at least the potential to become a giant sequoia. The work of the chicory and the beetle will be in vain, however, unless some of the seeds fall on bare mineral soil. Both are essentially backup systems to the occasional reproductive explosion fathered by fire. Weeks following a hot fire, the ground is peppered by a seed fall as much as 20 times the yearly average. Incineration of litter and dust on the forest floor provides the bare mineral soil needed for successful growth. By killing competitive trees, fire opens the forest canopies so that sequoia seedlings can receive the sunshine they must have. High temperatures kill insects, fungi, and other microscopic organisms that attack both seeds and seeding roots. The seeds of white fur and other more shade-tolerant species are baked in the soil beneath the fire. High temperatures also make the soil of the Sierra Nevada crumbly and wettable. Both conditions required for the infant trees to get a roothold. The policy of suppressing fire in sequoia grows has tended to frustrate the tree's adaptations to its environment and to endanger its survival. Beginning in 1886 in Yellowstone, park policy was to put out all fires. The National Parks Act of 1916 emphasized the protection of objects, including trees, rather than preservation of natural processes. Yet fire is the giant sequoia's greatest ally in its struggle to reproduce and continue its kind. Since the late 1960s in Yosemite and in sequoia and King's Canyon National Parks, lightning set fires at higher elevations have been allowed to burn. Prescribed burning by the park service has been conducted at lower elevations. The prescribed fires are applied in relatively small patches much as natural fires burn. The long-term goal is to establish conditions that will allow natural processes to take over in the forest without further intervention by man. Wildlife is not greatly disturbed by small fires. Many species benefit from the changes in vegetation that fire sets in motion. In this respect, they are like the sequoia itself. The sequoia grows seem relatively static in size. Hundred-year-old trees are growing along several boundaries. The young spire tops let their start after the last major fires. And if conditions for seedling growth improve, the grows may expand in the future. The existence of scattered sequoia communities along the central Sierra is a wonder and a mystery locked in nature. But fresh insight into the giant's reproductive strategy gives hope for a long-term species survival. Working to re-establish the natural wedlock of tree and fire, man may yet help the forests find their own destinies in their own way. The giant sequoia has one last immutable friend, time. The big tree can afford to wait. Wait a hundred, five hundred, or a thousand years. Wait for the hot fire to open the forest to its young. The tree is so ancient and so tenacious of life it is not soon likely to disappear. Even in death, flat in the wet ground, the heartwood of the giant seems to endure forever. She and still unborn will come to admire the groves and never see the end of the oldest tree among them. Time is confined to his meager three-score and ten. But no one truly knows how long the giant sequoia may live.