SEQUOIA GIGANTEA IS OF AN ANCIENT AND DISTINGUISHED FAMILY
There are two kinds of sequoias: the Sequoia gigantea of the Sierra Nevada, and the Sequoia sempervirens of the central and northern California coast. The two are members of the same sequoia genus. Both may be called sequoias. The sequoia of the mountains is the giant sequoia, and coast redwood is the accepted common name for the other. The following table compares the two species.
The two sequoias of today are all that remain of many species that once grew widely in every northern hemisphere continent, and the fossil record of the sequoia genus extends back a hundred million years or more in geologic time. The coast redwood once grew abundantly throughout North America, and in western Europe. The fossil record of the giant sequoia by comparison is very meager. Its fossils are few, and are restricted to western United States. We can only speculate, but perhaps this tree was always a mountain tree growing where the opportunities for entombment and fossilization were infrequent.
As world climates changed during the latter part of the Cenozoic era, first toward drier, then colder conditions, some species of sequoia became extinct, and the range of the surviving ones became more and more restricted. Only along the coast where the climate is moist and temperate did the coast redwood find conditions favorable for its survival.
Something similar must have occurred in the case of the giant sequoia. Today these trees do not form a continuous forest as is more or less the case with the coast redwood, but are separated into individual groves, distinctly and in some cases widely separated from each other.
This is a surprising circumstance, but perhaps at one time these trees did in fact comprise a more or less continuous forest along the entire length of the Sierra western slope. Just as the glacial advances during the Great Ice Age restricted the range of the coast redwood, so the alpine glaciers that moved down the Sierra canyons may have cut this continuous forest into isolated groves. In the glacial canyons, and near the glaciers, the sequoias disappeared. In the areas between the canyons, sufficiently removed from the frigid glacier influence, they persisted. Time has not been sufficient since the last glacial advance to determine whether these separated groves will eventually reseed the areas between sufficient to establish communication with each other. This is not surprising when you consider, for example, that the General Sherman tree is approximately 3,500 years old, and that a minor glacial advance occurred as recently as 5,000 years ago. In fact, six or seven generations of trees the age of General Sherman would take us back to the climax of the last glacial period. Truly, the giant sequoia is "a living link with the geologic past."
Until quite recently only the giant sequoia and the coast redwood were known`to be living. During the mid 1940's a Chinese botanist found in Central China what at first appeared to be a new species of tree. Examinations of the wood, foliage, flowers, and seeds by Chinese and American scientists disclosed an amazing fact. This new tree was identical to one long known from fossil remains found in wide distribution on all northern hemisphere continents, and already named the dawn redwood, Metasequoia glyptostroboides. Dr. Ralph W. Chaney of the University of California and Milton Silverman of the San Francisco Chronicle flew to China in 1948 to observe and collect seeds and specimens of this fossil tree come to life. There, growing in the same assemblage of plants with which it was associated in fossil bedsbirch, oak, beech, chestnuts and sweet gumwere the last remaining groves of the dawn redwood. Best known from its remains in the fossil beds of central Oregon, here was a tree alive and flourishing twenty million years after it was thought to have become extinct, and 10,000 miles removed from its last known habitat on another continent.
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Young sequoias grow more rapidly than the other evergreens, and in favorable sites easily overtop the firs, cedars, and pines planted at the same time.
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Young sequoias growing along the roadside seem to luminesce under light reflected from car lights. Their greater shine from reflected light distinguishes them from the neighboring pines, firs, and incense cedars.
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Sequoias are remarkably resistant to decay and insect attack. Several boring beetles do work in the wood, particularly of the branches, and others live upon the foliage, but we know of no case where insects have become epidemic on the sequoia, nor where they have resulted in the death of the tree.
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The dead tops of older trees may be from lightning damage, from breakage under the weight of winter snow or from wind, but may be the result of a restricted flow of sap between the foliage and roots caused by severe injury at the base of the tree.
Last Updated: 02-Feb-2007