I’ve been asked many times to calculate the age of trees that were in danger of being felled and to determine the average age of a stand of trees. It can be a fun educational exercise.
If you’d like to have your kids or students engage in a hands-on activity, estimating tree ages requires few materials and you will be happy to know to determine tree age, pro skills are not required at all.
What is worth knowing about how old a tree really is? And how can you measure the age of a tree?
Tree age is important information to scientists and horticulturists. For the forestry industry it can:
- determine the average age of a stand of trees.
- provide information on how quickly trees are growing.
- show the relative quality of a forest site through the average height of the dominant tree species at a specific age.
- predict the future monetary value of the site when harvesting trees.
- allow foresters to predict the productivity of the land for trees and wildlife.
- determine the benefits of a tree ecologically and economically.
- Determine what trees to plant and where.
Estimate a Tree’s Age
Wrap the tape measure around the tree at about four and a half feet above the ground. This measurement is the tree’s circumference. Write down this measurement.
Use the circumference to find the diameter of the tree. The formula for finding diameter is: Diameter = circumference divided by 3.14 (pi).
Determine the age of the tree by multiplying the diameter by the growth factor. Here are the growth factor rates for common trees found at hunker.com.
2.0: Aspen, Cottonwood
3.0: Silver Maple, Pin Oak, Linden
3.5: River Birch
4.0: American Elm, Green Ash, Red Oak
4.5: Black Walnut, Red Maple
5.0: Sugar Maple, White Birch, White Oak, Black Cherry
7.0: Dogwood, Ironwood, Redbud
For example, say a Silver Maple has a circumference of 20 inches. The diameter (20 divided by 3.14) is 6.369. The diameter (6.369) x growth factor (3.0) = 19.108. The tree is approximately 19 years old. Simple.