The Living Forest: What Tree Rings Tell us About the Life of a Tree

Trees are great record keepers, they tell us so much about the past. They are also resilient organisms, outliving humans and animals. Some of the oldest trees in the world are thousands of years old — like bristlecone pine. They’ve lived through major environment changes, climate shifts, and numerous historical events. There are trees standing today that are older than the establishment of this country, how remarkable.

We can learn a lot from trees, but first we must understand them.

Every year, trees form new growth rings (also called tree rings). Not only do these tree rings tell us the age of a tree, but they also tell us climate conditions during the life of a tree. Trees add a new layer of wood between the bark and the trunk each growing season. The wood formed in spring grows faster and lighter and consists of larger cells. In the late summer, growth is slower, so the wood has smaller cells and is darker. One light ring and one dark ring represent one year of the tree’s life. Additionally, a young seedling will grow faster than a mature tree. So, growth rings may become progressively smaller as the tree ages.

Since trees are sensitive to climate conditions like temperature, moisture, and sunlight, their growth reacts to these factors. Wider tree rings may indicate a warm, wet year, whereas fine tree rings can indicate a cold and dry season. Additionally, finer tree rings may indicate distress from fire, pests, or disease.

Read 3 Things You Should Know About Climate Change

Many factors affect the way the tree grows, altering the shape, thickness, color and uniformity of the rings, so tree rings will read differently. Factors like tree species and geographic location can impact the size and growth of tree rings. Long-lived species like oaks will have narrower tree rings, while species like willows and aspen will have wider rings because of their short life cycle.

Check out this timeline to see the life of a loblolly pine and factors that affect the tree’s growth rings.