The age of a large, woody tree can be determined accurately only by an actual count of the annual growth rings on a cross section of the stump or butt log after the tree is cut down.

Fortunately, the age of each tree is recorded in the wood of the

Cross-section of a Giant Sequoia showing growth rings back to A.D. 58.

From Shirley, Redwoods of Coast and Sierra, courtesy University of California Press.

THE HISTORY OF A GIANT SEQUOIA

As illustrated by a section (bark to center) from an individual which for nearly twenty centuries lived in the Nelder Grove in Sierra National Forest. Familiar events of the Christian era which occurred within the lifetime of this tree are named at the left; on the right are indicated the corresponding periods in the growth of the tree. It was 57 feet in circumference at base, 234 feet high, when cut down.

trunk. Just between the bark and the wood of a tree, there is a thin layer of cells known as a “cambium.” The cambium is the growing tissue of a tree. It covers the top and sides of the wood of a tree like a cone. Each year the cambium forms bark on the outer side and wood on the inner side. The slight difference in the appearance of the wood cells produced in the spring from the darker ones produced in the summer makes it possible to count the annual rings of growth. These annual rings are wider in the early life of a tree, and much thinner as the tree grows older. Further, the size of the tree is not always an accurate guide to its age, as the annual ring of wood may vary in width according to the difference from year to year in climatic conditions. Thick rings indicate long favorable seasons and prosperous growth, and thin rings record years of excessive drought or short cold seasons with consequent stunted growth. For example, ring counts made on two giant sequoias, both about 15 feet in diameter above the butt swell, revealed that one was 2,410 years old and that the other was a mere youth of only 1,740 years. Such counts made on a large number of giant sequoias of various sizes reveal that there may be a wide variation in the age of trees of approximately the same size.

The late Ellsworth Huntington of Yale University made a study of climatic changes reflected in the annual growth rings of the giant sequoias. From a curve based on this information he was able to show a correspondence with the historic rise and fall of nations from 1500 B. C. to the present, and concluded that historic changes may have occurred in response to climatic pulsations. He assumed that the thicker the annual rings of growth, the heavier the precipitation had been, whereas Waldo S. Glock in summarizing the evidence concludes that the reverse is true in the case of the giant sequoia. The heavier the precipitation, which is mostly snow, the shorter becomes the growing season, thus limiting the thickness of the annual rings of growth.

Claims of great age have been made for many species of trees. In practically every case where careful study and comparisons of very large trees have been made by scientists, age estimates have been materially reduced from the claims made by enthusiastic boosters, in some cases to less than 1,000 years.

Actual ring counts on many fallen and cut giant sequoias show that the age of this species frequently exceeds 3,000 years. John Muir writes, “The wood-rings in the section I laid bare were so involved and contorted in some places that I was not able to determine its age exactly, but I counted over 4,000 rings, which showed that this tree was at its prime, swaying in the Sierra winds, when Christ walked the earth. No other tree in the world, as far as I know, has looked down on so many centuries as the sequoia, or opens such impressive and suggestive views into history.” (Mountains of California.) Another authenticated ring count proved an age of 3,210 years and some of the larger trees may exceed 3,500 years.

An estimate of the growth rate of a tree may be secured by using an increment borer to obtain a core showing the annual rings. It is not practical, however, to remove a core more than 2 feet deep in most trees, so that accurate information concerning only the more recent growth may be obtained.

All trees normally grow faster during their youth than in later life. For example, during the early years in the life of a giant sequoia, it may increase in diameter at the rate of about an inch every five years. One of our museum specimens actually increased its diameter more than one inch a year. However, in some veterans it may require more than 20 years to produce a one-inch diameter increase. Thus it is impossible to say with any degree of accuracy just how old a large, standing, living tree may be. On the basis of present verified evidence mature giant sequoias are the oldest living things on earth; and of all the giant sequoias, the Grizzly Giant in the Mariposa Grove, estimated at 3,800 years of age, is considered by many to be the oldest. However, the General Sherman and the President in Sequoia National Park have their supporters as contenders for this title.

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