Tree rings are like a diary of growth, written in the concentric circles of the trunk as it expands outward. RUTH SMITH / For the Monitor

Take Me Outside is a monthly feature exploring New Hampshire wildlife and the natural environment. Ruth Smith, earned a master's degree and state-wide and regional awards in environmental education. She has taught countless children and adults about ecology at several New Hampshire non-profit organizations. She lives in a solar-powered home on a small homestead farm in Canterbury. She is not a member of the Monitor staff.

When trees receive adequate sunlight, water and nutrients, many species can live for decades or centuries. During their lifetime trees will experience a variety of conditions and events which impact their growth. Those events leave clues which reveal the history of the tree and its surroundings many years later.

Tree rings are like a diary of growth, written in the concentric circles of the trunk as it expands outward.

Counting the rings is possible because of the different seasons of growth. In the spring and early summer rapid growth occurs creating large cells and light colored wood. Late summer growth is slower, the cells are smaller and closer together and the wood is darker. By fall growth stops, marking a clear line between each year (at least for trees in temperate zones). Therefore counting the dark rings (or the light rings) will provide an accurate tally of the age of the tree.

There is more than chronology that can be learned from examining rings. When I recently scrutinized the stump of a 90-year-old white oak, the rings in the center were significantly wider than the ones on the outer portion of the trunk. The tree likely received more sunlight and had less competition when it was a young seedling. As it got older and other trees were closing in around it, the amount that it grew each year diminished greatly.

The rings shared more stories. As I counted in from the bark toward the center, when I reached the wood that had been added 40 years ago, there was a dramatic difference. During 1981, the non-native gypsy moth caterpillars (now called the spongy moth) devastated the forests from Maine to Maryland. Consumption of leaves (especially on oak trees) by these caterpillars created the greatest deforestation ever recorded in the Northeastern US, according to the US Forest Service.

Without foliage, a tree can’t produce the carbohydrates that enable growth. In 1981, the growth ring was tiny in comparison to years before and after that year. Even if you didn’t experience or know about the gypsy moth outbreak, you could tell from the growth rings that something significant happened in that year which negatively impacted the growth of the tree (and all the others around the area).

Defoliation is one thing that can reduce growth, other impacts such as drought, immediate competition for light or fire can create changes in the rings. The reduced light or fire might impact only one side of the tree, causing an uneven growth ring that is narrow on one side of the tree but wider on the other. A fire may leave a charred mark that is enveloped by new wood, but shows up when the trunk is opened, revealing a traumatic event and a bit of land history that the tree trunk can tell.

Tales of activity can also be visible from the outside of the tree. Strange growth patterns result when ice storms break branches or wind topples or bends trees. There are places where you can still see evidence of the 1938 hurricane or the ice storms of 1998 and 2008.

Patterns of holes can indicate that woodpeckers have sought insect meals from within the tree. Large pileated woodpeckers carve out rectangular feeding holes sometimes large enough to insert a soda bottle. Diminutive downy woodpeckers leave much smaller feeding holes with jagged edges. The yellow-bellied sapsuckers create lines of small round holes that look like someone took a drill to the tree. In this case the birds are “tapping the tree” to get the sap to run. They lap up the sap along with any insects that are attracted to the sticky liquid.

Human-made drill holes, especially in maple trees indicate that sap has been collected for making maple syrup. These tap holes close up in a year or two, covered over by new wood, but if you cut open an old maple tree, it is common to see the scars from many years of sap harvesting.

The next time you are in the woods, whether you find a newly cut stump or a standing tree, look carefully for clues to past events, you may learn some history written in the chapters of the tree book.

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