Michele Sue Anderson, age 102 of Phoenix, AZ for her question:

How are tree rings formed?

An ancient sycamore may stand 125 feet tall. It could be 350 years old. An old bur oak may stand 170 feet tall„ It could be 500 years of age. But we cannot be certain of the ages of these trees until they are cut down. Then we may count the banded rings on a slice of the trunk.

In a flat board of wood; the grain runs in grooves from end to end, A slice across the trunk gives a different view of these groove. Here they run in circles, one outside the other,

Lets fell and examine the old oak, Each ring of lighter wood is banded with a thin, darker line. Each lighter ring is softer and much wider than its dark rim, It was made in the growing season when sunshine summer making plant food, Some of the food was used to make a new layer of wood around the outer edge of the tree trunk.

Under the bark is a special layer of wood‑making cells called the cambium. Cells of the cambium can divide, producing daughter cells, Most now cells are Produced on the inner edge of the cambium. These are the woody cells that build the tree rings, The outer edge of the cambium produces calls of now bark, '

In summer the new woody cells are large. Food is plentiful and new wood is needed to carry supplies up and down the tree trunk. In winter, the woody cells are smaller and packed close together, Those are the slim bands of dark wood that border the wide ring of light, summer wood. Each years growth should show a ring of lighter wood.. fading to a dark rim, '.

Some of the rings on our oak are wider than others. They were made during the very good growing seasons. Some are narrow, They were made in dry summers. One has fuzzy darker lines among the light wood. Here the summer was a measure of rain and long droughts. The rings say our tree was ten‑ years old, They also give us a record of the weather  for 300 seasons,

The sycamore turned out to have a hollow trunk, We cannot count its ago. But we can see why a tree has to grow new wood every season. The inner heartwood of the tree is old and dead. Its only use is to give support to the trop trunk. The tree can stay healthy and keep on growing even if its heartwood is rotted away.