How to Calculate the Age of a Tree
Professional foresters and arborists often determine the age of a tree using the calculated estimate method. The only way to revel the exact age is counting the rings when the tree dies or taking a sample by increment boring, however the calculated estimate method does not damage the tree.
Cut off the largest dead branch on the tree. Cut a thin slice or "tree cookie" from the widest part of the branch and paint the tree cookie with stain to enhance the growth rings. Use a clear stain or linseed oil on dark woods such as cedar or walnut and a dark stain on lighter woods such as maple, ash and white oak. Allow the stain to dry.
Measure the average growth rate per inch with a ruler. Trees grow two rings per year; one is darker and one is lighter. Calculating the average of all the rings adjusts for uneven growth caused by weather patterns, insect invasions and other environmental stressors.
Measure the circumference (distance around) of the tree trunk right above the root flare. This is usually about 4.5 feet above the ground. Professionals call this diameter at breast height (DBH). Have a helper hold one end and circle around the tree with a cloth measuring tape or a piece of string. Divide the circumference by Pi (3.1415). This gives you the diameter (distance from one side to the other). Divide this by two to get the radius (the distance from one side to the center). If there is more than one trunk choose the the largest one for your measurement.
Divide the radius by the average from the tree cookie and you have a very good estimate of how old your tree is.
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