This week’s question was asked by Victoria Semelroth, fifth grade, LaGrange Elementary School.
Teacher: Chelsey Juliot.
QUESTION: Why do trees have rings?
Tree rings can be seen on a stump or log when a tree is cut down. Each ring equals one year of growth. Counting the rings is one method of telling how old a tree is. Tree rings are more noticeable in our northern climates where seasons change from hot to cold so there is a large change in growth speed through winter, spring, summer, and fall. Some trees in the south don’t appear to have tree rings.
Tree rings grow in the cambium layer that is right under the bark. The bark is pushed out while the tree is growing. New woody cells are laid down each year. The cells are the building blocks that produce new layers of wood. The lighter wood is known as the early wood, with lots of water present. This wood is laid down in the springtime. The darker, denser wood is added on in the summer and fall when less moisture is available. The growth rings are more easily seen in pine and spruce (conifers) and hardwoods such as oak, ash and walnut.
Tree rings tell scientists a lot about the weather and climate. If a tree receives lots of water, sun and space to grow, the ring will be thicker. Thinner rings indicate the tree is stressed and not receiving the resources needed for growth.
Trees are some of the oldest living things on Earth, having been in existence for 350 million years. The bristle cone pine can reach an age of 5,000 years. People in California have counted 3,000 rings on a few redwood trees. Tree growth rings can tell us about the ancient climate.
Tree rings can divulge secrets of drought, severe storms, temperatures, soil pH, CO2 concentrations, attacks by insects and disease. Tree rings are used to check the accuracy of radiocarbon dating. Growth rings can also be used to date the wood in old buildings, ships and frames for paintings.
It makes sense that drought decreases tree growth, producing a narrower ring. If a tree is crowded by neighboring trees, there will be a series of narrow rings. If the rings are narrow on one side of the tree with wide rings on the other, the tree was crowded on the side of the tree where the rings were narrow. Fire scars suggest past forest fires. The number of annual rings between fire scars show the period between fires. Certain scars can indicate insect infestations.
Counting tree rings was a pastime for the three Scheckel boys growing up on the Crawford County, Seneca-area farm in the 1940s and 1950. We cut big trees for logs to haul up to Vedvik’s saw mill in Seneca. Limbs became fence posts and firewood. Those trees were felled by a two-man crosscut saw, mind you. No chainsaw for the Scheckel boys!
We would guess the age of the tree before sawing, yell “timber” when it was ready to topple, then rush back to the stump to count the rings. No prize for the best guess, only bragging rights until the next tree fell.
You must read the chapter in Aldo Leopold’s 1949 book, Sand County Almanac, which he wrote after guiding a two-man crosscut saw through his lightning-killed oak tree north of Baraboo on the Wisconsin River in the 1940s. As he and his family cut, Leopold reflected on events during the tree’s 80-ring lifetime, roughly 1865 to 1945.
He wrote, “Fragrant little chips of history spewed from the saw cut, and accumulated on the snow before each kneeling sawyer. Our saw was biting its way, stroke by stroke, decade by decade, into the chronology of a lifetime, written in the concentric annual rings of the good oak.”
A final tidbit about tree rings. The Little Ice Age occurred from 1300 to 1850, the worst period from about 1645 to 1750. It brought such low temperatures to northern countries that crops could not be grown. Thousands, if not millions, died of starvation. New York harbor froze over and people walked from Manhattan to Staten Island. Two feet of snow fell in New England in June and July. The Little Ice Age froze the Vikings out of Greenland, accelerated the Black Death, helped trigger the bloody French Revolution and destroyed the Spanish Armada.
It was so cold throughout Europe that tree growth was stunted, resulting in unusually dense wood. It is this rare dense wood that contributed to the beautiful tonal properties of violins made by Antonio Stradivari.
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Larry Scheckel is a retired Tomah High School physics teacher.
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