THE QUESTION is often asked, "Why do the Sequoias live so long?" The answer is probably to be found in the fact that, whether dead or alive, they are remarkably resistant to the natural enemies of the forest. In general, there are three important enemies of dead or living mature trees: namely, insects, fungi, and fire.

Insects—killers of forests.—Oaks may be harmfully affected or killed by as many as two hundred different kinds of insects. Many other trees are killed by insects, or are so weakened by them that they die from decay. Great numbers of Sugar Pine and of the western Yellow Pine have been killed by beetles, but the Sierra Redwood, although it grows in the same forests, seems to be quite free from any serious affection by any insect. The Coast Redwood is sometimes attacked by the larva of a very small insect which reduces the bark just under the surface to a fine powder; this does not, however, imperil the life of the tree.

Not only is the living Redwood tree very resistant to the work of insects, but so is its lumber. In tropical regions, among the worst destroyers of wooden houses are the termites. These insects (incorrectly called "white ants") are a type of social insect living in colonies. Their food is chiefly cellulose, a substance which forms a rather large part of the composition of all plants. The termites, acting as nature's scavengers, reduce the brush and debris of forest and jungle to a condition from which is developed humus or mulch. Numerous species of termites are found in the Tropics, of which at least three are of economic importance in the United States. Sapwood (which is the outer cream-colored wood just under the bark) even of Redwood is not naturally termite-resistant; but Redwood lumber made of heartwood and used in the Philippine Islands, Mexico, and the United States has successfully resisted termite attacks for from forty to fifty-five years.

Fungi—slow destroyers of forests.—Fungi are colorless plants that are not able to manufacture their own food, but must use extraneous materials. Saprophytic fungi, or saprophytes—for example, mushrooms, bread mold, and puffballs—live on dead substances; parasitic fungi, or parasites—for example, corn smut, wheat rust, and grape mildew—live on living plants. Fungi often kill living plants and cause dead plants to become decayed.

Redwoods have seldom, if ever, been known to die from attacks by fungi. Most other trees, if injured by fire, or by the careless breaking of limbs, soon become infected with fungi, and are likely to die as a result. Both species of Redwood are indeed often found with a small amount of "heart" rot, but since heartwood is nonliving tissue the life of the tree is not imperiled. It is probable, however, that many of the trees become so-called chimney or telescope trees through the burning of the "rot" at the center of the tree.

COAST REDWOOD TREE OF MUIR WOODS, DAMAGED BY FIRE BUT NOT DESTROYED Courtesy of Muir Woods National Monument

The unusual resistance of Redwoods to the attacks of both insects and fungi is thought to result from the presence, among other chemical agents, of a chemical known as tannin. This is a substance occurring in hemlocks, oaks, and many other trees, from which it is extracted and used in tanning leather. It has also been used recently as a remedy for burns on the human body. The Redwoods have a high percentage of tannin, and this gives both the bark and the heartwood a reddish color during the life of the tree. Tannin is also abundant in the cone, where it forms about seven-tenths of the substance known as cone pigment. If a tree falls and breaks, the tannin soon covers the broken ends of the tree, giving it the appearance of having been burned or creosoted, and this natural treatment protects the wood from decay.

Among the earliest white settlers in California was a small band of Russians who established a colony in the Redwood country at what is now Fort Ross, Sonoma County, about 100 miles north of San Francisco. This Russian colony more than a hundred years ago built numerous buildings hewn from the native Coast Redwood. One of these buildings, a church, still stands at the original site, and is a notable example of the durability of Redwood. As telegraph poles, piling, tunnel timbers, tanks, bridge towers, pipe lines, fence posts, bridges, sills, railroad tunnel timber, floor joists, and railroad trestles, Redwood has persisted with remarkably little decay for periods ranging in duration from 30 to 150 years.

Trees which have lain in the forest for centuries can still be used for lumber. In 1925, American Forests and Forest Life reported the following example of the durability of a Redwood which had been down for more than 340 years. Three hemlocks, 235, 250, and 340 years old, respectively, were growing directly over a Redwood, which was 78 inches in diameter. The living hemlocks had evidently started from seed that had lodged on the fallen Redwood trunk, and there sprouted. The roots of the seedlings continued to grow on and around the fallen tree until they gained a foothold in the surrounding soil. The fallen tree was still in a sound condition.

SIERRA REDWOOD TREE GROWING NEAR AURORA, NEW YORK Courtesy of Clyde Fisher

Fire—quick destroyer of forests.—Fire is the great quick destroyer of forests. Acres upon acres of the finest forests of the world are consumed annually by destructive fires. The pine and the fir trees are highly inflammable because of the pitch they contain. Evidence of early-day fires is apparent in many places throughout the Redwood regions, and many of the fire scars can be used to date the time of the occurrence of the fires.

Redwoods, however, contain neither pitch nor resin; furthermore, since the asbestos-like bark grows to at least one foot in thickness in the Coast Redwood, and often as much as two feet in thickness in the Sierra Redwood, fire seldom is able to kill these trees. Once in a great while, fire will go up the trunk of a Sequoia, burn the crown, and thus kill the tree. Both kinds of Redwood are thus exceedingly resistant to fire and its effects. Of course, hot fires will kill the young Redwoods, but once the trees have reached maturity they are not easily killed.

Although Indians have been blamed for setting fires which have burned Redwoods, probably many of the fires, if not all, were started by lightning. As many as six lightning fires have been known to occur in the Yosemite in one day. If fires have occurred no oftener than once in a hundred years, some of the older trees must have been attacked at least twenty times in their lifetime. Once a fire was started, it swept through the forest, burning pines, firs, and young Sequoias, but seldom killing a mature Sequoia. Most of the Sierra Redwoods show fire scars on the upper side, where dead branches and leaves have accumulated.

The Telescope Tree in the Mariposa Grove and the Chimney Tree in Big Basin show how these trees may continue for centuries to remain vigorous though their heart is burned out. How can a tree continue to live with the heartwood burned out? The term "heartwood" is really a misnomer, in that it suggests the animal heart, which is essential to the life of an animal. Heartwood is composed of cells which have ceased to live. The outer layers of the wood of a tree, known as sapwood, are the live part of the wood. Through the sapwood, water and minerals are conducted up from the roots. Food is manufactured by the green leaves in the presence of sunshine, and the food is conducted down to the various parts of the tree through the inner layers of bark.

Since the Sierra Redwood does not sprout from the base, trees which have been killed by fire cannot continue to reforest the area. The Coast Redwood, however, reproduces abundantly by forming sprouts around the base of parent trees. There are sections of country along the Redwood Highway where farmers have tried to use cut over Redwood land for agricultural purposes. But even after as many as ten successive years of heavy burning of the stumps on a cut-over region, sprouts have still continued to come up, so that the farmers frequently surrender to the persistent Redwoods.

YOUNG SIERRA REDWOOD IN MARIPOSA GROVE Courtesy of Yosemite National Park