Estimating Tree Age Based on Diameter and Species
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| A 52-year-old Zelcova tree |
Suppose you’re out on a walk or a bike ride and you spot
a very large tree. Perhaps it’s very
tall, it has a massive trunk, or its branches spread in an enormous canopy. One of your first questions might be, how old is that tree?
You could cut down the tree or use a tool called an increment borer so
you could count the growth rings. However, cutting the tree down obviously kills the tree and
the increment borer can damage the tree by making holes in it. What other options are there?
To get an age estimate in a non-invasive way, you can determine the diameter and calculate the age as follows:
- Determine the species using a tree identification book or a cool online site like this one.
- Using a tape measure, determine the circumference of the tree at 4.5 feet (54 inches) above the soil.
- Calculate the diameter, which is circumference divided by pi. The value you get is the DBH or diameter at Breast Height, which is that 54 inches above the ground.
- Multiply by the species-specific growth factor in the table below or by looking here:
Tree Species
|
Growth factor
|
Red maple
|
4.5
|
Shagbark hickory
|
7.5
|
Sweetgum
|
4
|
Douglas
fir
|
5
|
Sugar maple
|
5.5
|
White oak
|
5
|
Cottonwood
|
2
|
American
sycamore
|
4
|
American beech
|
6
|
Here’s an example.
For the Zelcova tree shown below, the circumference at 54 inches above
the soil was measured at 131.5 inches.
The diameter (DBH) is then 131.5 inches divided by 3.14 (pi) or 41.87
inches. If the growth factor for a yard-grown Zelcova* is 1.24, so we multiply 41.87
inches X 1.24 years/inch = 51.9 years.
 |
| Measuring circumference at 54 inches. |
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| The circumference is 131.5 inches and the tree is about 52 years old! |
For further information:
1) To determine tree species, try http://www.arborday.org/trees/whattree/
2) To learn more about species-specific growth factors in years/inch try:
3) To learn about the 10 most common trees in the United States try:
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