How Do Trees Record Time?
ES2905  Records from the Past
USDA Online Photography Center

Some species of trees can live for thousands of years. Because the widths of a tree's rings reflect yearly precipitation patterns, the rings can be analyzed to reconstruct a record of past climate conditions.

Tree rings also record the occurrence of forest fires. New layers of wood added around the exterior of tree trunks are vulnerable to damage by fire. If a fire damages a tree's bark and exterior, but does not kill the tree, a new layer of wood can grow over the scarred layer the next year, preserving the scar as a record of the fire.

Evidence from tree rings indicates that the climate of the southwestern United States has experienced long periods of drought. These drought conditions are related to higher frequencies of forest fires.

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