“How can you tell the age of a tree?” asked Bill.
“That can’t be done until the tree is cut down,” said Cecil. “Each year during the life of a tree a complete coating of fibre is formed around the trunk of a tree underneath the bark. These coatings take the form of rings and are called ‘Annual Rings.’ They are formed in regular sequence around the center. By counting the rings the age of the tree is determined.”
“Why go to all that trouble?” asked Bob. “If there is one ring for each year and the rings are all the same size, why not measure the diameter of the tree and divide by the distance between the rings?”
“It would be much simpler if we could do it that way, but unfortunately the distance is not the same in any two different kinds of trees, or even in the same tree,” replied Cecil. “There are many things that affect the growth of trees. For instance, if a young tree is crowded for light and room, the rings will be very close together. Then if the surrounding trees dies or are cut down and the crowded condition relieved, the young tree will grow much faster and the distance between two rings may be the same as that between seven or eight rings during the period of slow growth. Two trees growing side by side, although they may be of the same species, may have entirely differently spaced annual rings.”
“That depends upon the species,” replied Cecil. “One of the giant trees in the Sequoia National Park was undermined by a creek a short time ago and fell. That, as you know, was a Redwood. They made a cross section of that tree seventy feet above the base and it measured eleven feet in diameter. The tree was 280 feet tall and had a base diameter of twenty-one feet. The annual rings showed it to be 1,932 years old. Of course those trees are the oldest living things in the world.
“Other species do not get so large in the trunk but grow higher. You yourself remarked about that flagpole at San Francisco. That tree must have been over five hundred feet tall when it was standing here in these woods, and yet its trunk probably did not measure over fifteen feet in diameter. You can see some of the large Douglas fir and pines over there. They have not such large trunks but their tops are well up in the air. The average is well over three hundred feet. Take the Juniper, for instance; it is rare that we find one over ten feet in diameter. The foresters in Nevada made quite a news item out of one they found up in the mountains at the head of Broncho Creek. It was located at an altitude of about eight thousand feet and was a monster of its kind. For its diameter near the base was fifteen feet. It is rarely ever that we find a black walnut over fifty inches in diameter when fifty years old. An inch a year is a rapid growth for that tree.