A tree's age can also be measured by counting the annual growth rings within the tree trunk. There are two ways that you can count growth rings. The first way is to count the rings on a log or a tree stump after a tree has been harvested. The second way is to use a tool called an increment borer to remove a small core of wood from the tree. After extracting the core, just count the rings as you would on a log. By using an increment borer, our foresters can tell a mature tree's age without risking the health of the tree.