How Old is This Tree?

By Jan Jackson –

Greg Schmitz, President and CEO of Schmitz Timber Management

I visited a logging site a few weeks ago, and took some photos of a pile of logs ready to be trucked to the mill. This close up photo of a Douglas fir log shows the rings you need to count to tell how old the tree was. A tree adds new layers of wood to its trunk each spring and summer, so all you have to do is count the dark rings. This tree was probably planted in the early 1960s. It’s soon going to be made into lumber, timbers, pilings or plywood for somebody’s house and thanks to the Oregon Forest Practices Act of 1972, a new tree will be planted in its place.

If you want to know how old a tree is that is still living, go to or read the following excerpt from their website:

Estimate a Tree’s Age

Step 1

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.

Step 2

Use the circumference to find the diameter of the tree. The formula for finding diameter is: Diameter = circumference divided by 3.14 (pi).

Step 3

Determine the age of the tree by multiplying the diameter by the growth factor. Here are the growth factor rates for common trees:

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.

Related story: Working in the Woods

Photos by Jan Jackson
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