Estimating Tree Age

Estimating tree age can be done through the use of the species' growth factor. For instance, the growth factor for Douglas Fir trees is 5. This means that in 5 years, the tree's diameter at 4.5 to 5 feet above ground increases by one inch.

Since directly measuring the tree's diameter is difficult, we can use the value of pi to help out. Here's how to estimate the age of a Douglas Fir by measuring the tree's circumference:

1. Locate the spot on the trunk that is 4.5 to 5 feet above the ground. If the ground is sloped, find a middle point in the slope.
2. Measure the circumference of the tree at that height in inches.
3. Multiple that measurement by 1.6. The result is the approximate age of the tree.

Example

A tree with a circumference of 57 inches at 4.5 to 5 feet above the ground has an approximate age of 91 years.