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AGE A TREE WITHOUT CUTTING IT DOWN

Everyone knows the easy way to age a tree—cut it down and count the growth rings. The trouble is there’s an obvious flaw in this method: it kills the tree.

Fortunately there are several other ways to age a tree without resorting to this terminal solution. Here are four of them.

CORE EXTRACTION

You can use a specialized drilling tool to count tree rings without damaging the tree. An increment borer is a special drill consisting of a handle, a drilling bit, and a small core extractor that fits into the auger bit. Drill into the tree at chest height using a borer the length of which is at least 75 percent of the tree’s diameter. Put your body weight into the first few turns to get it going, making sure to keep the drill horizontal.

Keep turning the handle until the end of the well-lubricated drill reaches just a little farther than half way (i.e., just past the pith—the tree center). While the tool is still in the tree, carefully introduce the core extractor through the back of the drill. Make sure the open side of the extractor is facing downward. Then make one-half turn of the drill in the reverse direction and then slowly withdraw the core extractor. Now count the rings. Most trees produce two rings each year: one light spring ring and a darker summer ring. You can count either to determine the age of the tree. Add on a few years to allow for the early growth that won’t show up in your sample.

COUNT THE WHORLS

Each year a new whorl is created when a bud bursts through the tip of the tree to form a new branch. In some species counting tree whorls (spiral scars on the trunk) can give a rough estimate of the age. Count the number of whorls above chest height and add one year.

COUNT THE GAPS

Count the number of gaps between branch sections, including the section at breast height, and above the last branch.

MEASURE THE CIRCUMFERENCE

Measure the circumference of the trunk about 5 ft (1.5 m) above the ground. Calculate the radius (distance from center of the tree to its outer edge) using the formula r = C/2Π (i.e., divide the circumference by 6.283). Then divide the radius by the average yearly tree growth for your tree species (available online) to find its age.