Each dark ring on a tree represents one year of growth; however, if you examine the shapes and patterns of the rings, you can learn about its history—from happy sunny days to darker times.
Rings that are spaced widely are happy! They’ve had years of good weather with lots of rain and sun. When a tree’s rings appear wider on one side than the other, it’s an indication something pushed the tree as it was growing and the tree will create “reaction wood” to compensate on the side that leans.
Narrow rings in bunches signify drought, lack of water over several years. Narrow rings and holes can depict insect infestation—the larva of the sawfly (or other insects) bore into the tree while eating the leaves and leaf buds.
If everything looks good but the growth appears to have slowed for no apparent reason, a potential reason is that other trees have taken the lion’s share of sun and water from their taller crowns and stronger root systems.
A fire in the forest or other scarring on the tree’s bark can create undulations while more wood covers the scar.