All winter long, the tissues that normally carry water up a tree to its leaves alternately freeze and thaw. This causes air bubbles to form that would prevent the tree from transporting water to new leaves in the spring. So in early spring, the trees will begin to produce a new ring of woody tissue, using energy reserves from the previous summer.
This new growth is called “early wood,” and its width reflects growing conditions in the previous year. Late wood, which develops later, is denser and lighter in color. The contrast in color creates the tree rings that we are all familiar with.
Also known as growth rings, they’re are easy to see on trees grown in regions with alternating hot and cold seasons. Tropical species, because they don’t experience the freeze/thaw dynamic, don’t show strong ring patterns.
We all know that growth rings can be used to determine a tree’s age. In addition, a scientific field known as dendroclimatology is using tree rings to produce detailed reconstructions of past climates.
Living Bristlecone pines, thousands of years old, have provided superb climate reconstructions for the American interior west. And ring patterns on dead trees and on lumber from buildings and archaeological sites, are allowing scientists to reconstruct important information about temperature, precipitation, sunlight, and other climatic conditions at different locations throughout the world.
Tree rings can tell a story. We should take the time to read it.
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Photo, taken on April 29, 2007, courtesy of Sheila Miguez via Flickr.
Earth Wise is a production of WAMC Northeast Public Radio. Support for Earth Wise comes from the Cary Institute of Ecosystem Studies in Millbrook, NY, with partial support from the Field Day Foundation.