Oaklee loves pi
Time for another edition of Oaklee Does Math for Pie! Actually, it’s pi day so we’ve enlisted everyone’s favorite squirrel to teach you a bit more about how to use pi to estimate the age of a tree.
For this exercise, you’ll need a tree (forest grown trees work best — trees out in the open grow at different rates depending on site conditions), measuring tape, and a calculator.
Step 1: Identify your tree and find it on the list (below).
Step 2: Measure up to 54 inches from the ground (4 1/2 feet). This is Diameter Breast Height, or DBH.
Step 3: Measure around the tree at DBH to find the circumference in inches.
Step 4: Divide the circumference by the mathematical pi π (3.14). This will give you the tree’s diameter (we learned that last year, remember?).
Step 5: Multiply the diameter by the growth rate number listed next to your tree species in the chart. This will give you the approximate age of your tree! For example, a white oak with a circumference of 126 inches would have a diameter of about 40 inches. Multiply that by the white oak’s growth factor of 5, and you’ll find your white oak is approximately 200 years old.
C/π=d, where C is circumference and d is diameter
d*gr=age, where d is diameter and gr is growth rate number
Growth Rate
| American beech | 6 | Norway spruce | 5 |
| American elm | 4 | Pin oak | 3 |
| American sycamore | 4 | Redbud | 7 |
| Austrian pine | 4.5 | Red maple | 4.5 |
| Black cherry | 5 | Red pine | 5.5 |
| Black maple | 5 | River birch | 3.5 |
| Black walnut | 4.5 | Scarlet oak | 4 |
| Bradford pear | 3 | Scotch pine | 3.5 |
| Common horsechestnut | 8 | Shagbark hickory | 7.5 |
| Colorado blue spruce | 4.5 | Shingle oak | 6 |
| Cottonwood | 2 | Shumard oak | 3 |
| Douglas fir | 5 | Silver maple | 3 |
| European beech | 4 | Sugar maple | 5.5 |
| European white birch | 5 | Sweet gum | 5.5 |
| Green ash | 4 | Tulip tree | 3 |
| Ironwood | 7 | White ash | 5 |
| Kentucky coffee tree | 3 | White fir | 7.5 |
| Littleleaf linden | 3 | White oak | 5 |
| Northern red oak | 4 | White pine | 5 |
| Norway maple | 4.5 | Yellow buckeye | 5 |
