Q: Is there some way, some formula, perhaps, to gauge the age of trees without cutting them down and counting the rings?—Jeff Moore, French River, Ont.
A: Yes, there is a formula, originally developed by the International Society of Arboriculture. It works because trees of the same species under the same conditions grow at roughly the same rate. Here’s how you can use it: measure the circumference of the tree’s trunk about 4.5 feet from the ground. Divide that by pi (3.14); this gives you the “diameter at breast height” (or the “DBH” in arborist lingo). You then multiply the DBH by the tree species’ typical growth factor (you can find charts online). This is a number assigned to each species that corresponds to how fast it typically grows.
The problem with this formula? In Canada, what’s typical varies widely. Different regions have different growing seasons, and “there are many factors that can influence a tree’s size,” says Steve Smith, an arborist with Bartlett Tree Experts in Calgary: soil conditions, root stress, water availability, or even light availability. “Trees that are in the understory of the forest often don’t grow as much in diameter as trees in better growing
