- Distribution

Photo: Five redwood seeds on  a penny .Present Distribution

Today giants sequoia grow and reproduce naturally only in scattered sites along the western slope of the Sierra Nevada. These sites are all within a 260 mile long zone at elevations between 4,000 and 8,400 feet. Even in these widely scattered places giant sequoia does not form pure stands as does the coast redwood. Instead, it occurs sporadically, scattered throughout a forest community made up of sugar and ponderosa pine, white fir, and incense cedar as well as a characteristic group of shrubs and smaller plants.

Graphic: Map of west coast with redwood distribution.

The most northerly grove of giant sequoias is near the middle fork of the American River in Placer County. It consists of only six trees, and is of particular interest because it is so small and so widely separated from the other sequoia groves. Recent reproduction seems to be extremely limited, and the grove may well be struggling against adverse environmental conditions. Toward the southern end of the giant sequoia range - in the Kings, Kaweah, and Tule River Basins - the trees are much more numerous, and they occur throughout broad areas, sometimes as few as two or three to an acre. South of the Converse Basin the sequoias form an almost continuous belt, with none of the groves being more than five miles from its nearest neighbor. Nevertheless, most observers continue to apply the grove concept and identify a total of sixty-five or as many as sixty-seven groves.

Past Distribution
As a species, giant sequoia has been traced as far as the middle Miocene epoch of the Cenozoic era, fifteen to eighteen million years ago. But the present-day giant sequoia and other redwoods of the past and present all belong to a family of trees - Taxodiaceae - that probably had its origin in the Triassic period of the Mesozoic era some 200 to 230 million years ago.

Graphic: Timeline chart.

By the beginning of the Cenozoic era, the "era of recent life," some sixty-five million years ago, the ancestors of our present-day redwoods were part of an extremely diversified plant community that was established in the middle and high latitudes of the northern hemisphere. The forest trees of this community included both conifers and deciduous hardwoods, such as oak, birch, elm, chestnut, and others. Among the conifers several redwood species were especially abundant. As Asa Gray maintained more than one hundred years ago, redwood-filled forests did in fact extend into the arctic regions in such places as Greenland, Iceland, Northern Siberia, and even Spitzbergen and Ellesmere Island, both of which are now located far to the north of the Arctic Circle.

Several species of Sequoiadendron were present in western Europe and in both western and eastern North America. As with other redwoods, these Sequoiadendron species were driven southward after the close of the Paleocene and may well have disappeared from Europe as early as the Oligocene or early Miocene some twenty-five million years ago. In North America a similar pattern of southward retreat and extinction was followed until finally just one species of Sequoiadendron remained. This was S. chaneyi, a tree that seems to have been virtually identical to our present-day giant sequoia.

As climatic conditions in Nevada and Idaho during the Miocene become generally cooler and drier, there was also a trend toward more extreme seasonal differences. As rainfall decreased still further toward the middle of the Pliocene, virtually all of west-central Nevada's forest trees were restricted to stream and lake borders, and then eliminated.

At this time, the mid-Pliocene, perhaps six to eight million years ago, the Sierra Nevada was much lower and had a warmer climate than at present. Geologists are not in complete agreement about the timing of Sierra Nevada uplift, but it now seems likely that during the middle Pliocene the northern part of the range stood at about one to two thousand feet elevation while the central part of the range had reached about three to four thousand feet. Once the range had reached this elevation, and later, toward the end of the Pliocene as it was lifted still higher, it began to have an increasingly strong influence on weather conditions - that is, its presence began to bring about conditions that were favorable to the development of a giant sequoia forest on the west slope and unfavorable to the continued survival of the older forest on the east. Giant sequoia had completely disappeared everywhere except on the Sierra Nevada's west slope by the time the great Pleistocene Ice Age began, perhaps as little as one million years ago.

In the Sierra Nevada, glacial activity seems to have reached its maximum extent 25,000 to 50,000 years ago. We can not be certain what happened to giant sequoias during this time. The most recent glacial advance, the Wisconsin, has been identified as the major reason for the present, widely separated or discontinuous occurrence of giant sequoia groves.

John Muir theorized that giant sequoia had probably once been widely and uniformly distributed along the western slope of the Sierra. Its present highly discontinuous distribution was due to its elimination from those valleys down which glaciers had advanced. Although his analysis of the impact of glaciation on giant sequoia distribution is still accepted in general, particularly for the northern half of the Sierra where glaciation was more severe, other climatic factors may have had a role in restricting giant sequoias to their present grove areas.

Excerpted from "The Enduring Giants" by Joseph H. Engbeck Jr., published by the California State Parks.