As a pine tree grows, the trunk and branches get thicker. Each year adds another layer of wood. Counting these new layers or rings determines the age of the tree fairly accurately, but cutting down a tree just to determine its age isn’t very practical or environmentally conscious. Other methods such as calculating the diameter of the tree or counting the whorls of a pine tree are useful tools for estimating age.

## Calculating Diameter

The approximate age of a pine tree can be determined by first calculating the tree’s diameter and multiplying the diameter by the growth factor. Measure the circumference of the tree trunk at about 54 inches above the ground or chest height. Using the formula of diameter equals the circumference divided by pi, calculate the diameter of the tree. A pine tree with a chest-high circumference of 70 inches has a diameter of about 22.29 inches.

## Growth Factor

The International Society of Arboriculture, the organization responsible for creating this formula, assigned a growth factor number to various species of trees according to their average growth rate. The white pine tree has a growth factor of 5. Multiply the diameter of the tree by the growth factor to determine the tree’s age. A white pine tree with a chest-high circumference of 70 inches is about 110 years old.

## Accuracy

Because the tree’s growth varies each year depending on climate conditions, the answer is only an estimate. Also, this formula is more accurate with forest-grown trees than with trees grown in the urban landscape because the growth factor is based on the growth rate of trees in the wild. Irrigation and applications of fertilizers by homeowners and park maintenance workers prevent maintained trees from experiencing true growth based strictly on natural condition.

## Whorls

The age of a pine tree can also be determined by counting whorls. As a pine tree grows each year, new branches form a circle, or whorl, around the trunk. The number of whorls is an approximation of the age of the tree. However, being able to see and count the whorls on very old trees may be difficult and impractical.

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