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  Nature Elective

The Age of Redwood Trees
First postedMay 3, 2004 Last updated June 30, 2004

Redwoods are some of the oldest plants on the planet. The tallest are our coastal redwoods, and the most massive are the giant redwoods. More information on the oldest, tallest, and largest, is here.

Bristlecone pine trees are the oldest, dating back 4,767 years. They are very slow growing pines, with some very old specimens found at Wheeler Peak, in the White Mountains of the southern Sierra Nevada. This tree is named Methuselah. It is mostly comprised of dead wood, with only a little living cambium and foliage. The climate conditions are very harsh, permitting only very slow growth. These same conditions, however, prevent rotting away of the dead wood and the preservation of the tree.

Giant redwoods can live to be 3000 years old. How do we know how old they are? Tree rings and dendrochronology! What's all this? Read on!


Trees do not grow at the same rate all year long. In the spring, the conditions for growth are better than they are during the winter. Therefore the cells laid down during the spring (called "early wood") are larger than the cells laid down during the winter (called "late wood"). This results in the formation of one light band and one dark band, which are merely alternating layers of larger cells that appear lighter in color, and layers of smaller cells that appear darker in color. Together these bands represent one year of growth. Counting the rings tells how old the tree is.

Redwood trees have been found in one study of old growth to have between 25 to 50 rings per inch of wood. A tree that is 8 feet wide could be 2400 years old. Second growth usually is faster, and the rings are not as close together.



The science of studying growth rings is called dendrochronology. It can yield insights into past climate conditions, forest conditions, dating of old wooden structures, and similar conditions.


We have a cross section of a redwood tree at Cazadero (seen at right) that is 350 years old. We have marked it with the birthdates of some of the important musicians: Mozart, Beethoven, Stravinsky. If you look at it, you will see that the redwood grew very quickly while it was young (the first 100 years), adding about 8 inches in girth. It grew slightly slower the second 100 years, about 6 inches, and then very slowly the last 150 years:only 2 1/4 inches! We have used this to calculate the age of our oldest trees, and we believe that they are 2,250 years old.