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Calendar Elm

Feb 27, 2012

Even mundane chores can lead to profound revelations. Yesterday I cut down a big elm tree whose rampant growth was shading out the part of my postage-stamp yard where I grow tomatoes. When the tree fell, I glanced at the stump and noticed something interesting.

The annual growth rings in the central 5 inches of tree trunk were so narrow they were nearly impossible to count. The growth rings in the outer 16 inches were several times wider, some exceeding half an inch. What set off this amazing growth spurt?

Out of curiosity, I counted the wide growth rings and came up with 23. That was an interesting coincidence; our house was built 23 years ago. Then light bulb went on. Twenty-three years ago, this elm was struggling to survive. It was in the midst of an overcrowded forest with infertile sandstone soil on a dry, west-facing slope. Overnight, it found itself on the edge of a clearing with its leaves basking in sunlight and its roots bathed in nutrient-rich seepage from the leach field of a newly installed septic system. No wonder its growth increased exponentially!

Getting rid of a dead tree had turned into an exercise in “dendrochronology,” the study of tree growth-ring patterns. The science got its start in the early 20th century, when astronomers discovered that the patterns in tree-growth rings recorded weather changes caused by sun spots. Then archaeologists began matching up the patterns in growth rings of trees living today with those that lived in the past. Eventually, they developed a continuous growth-ring chronology extending thousands of years back into history. That enables them to accurately date archaeological sites by the growth rings in timbers used to build ancient structures. Today, they even use dendrochronology to calibrate radiocarbon dating.

I will miss the elm. I have watched as many as 15 squirrels at once gleefully devouring its flowers and seeds in the spring. But I love my tomatoes, and I will always remember the lesson I learned from my amateur foray into dendrochronology.

Next time you find yourself looking at a tree stump, consider what secrets it might be trying to tell you.

Jim Low


Anonymous, I will add to Jim's comment that the tree had grown so tall and swayed so much during heavy wind that I was afraid it would blow down onto our home's roof. We have tried to preserve as many of the large trees as possible in our 5 acres. It is so nice to see the growth of the trees, especially those that are down in the bottomland. Since we don't like to mow anymore than the next person, we try to keep as many trees as possible while maintaining a healthy forest. Go ForestKeepers!

Thanks for your comment, Anonymous. Look at it this way. Our 5 acres supports approximately 1000 trees. Sacrificing one of those trees in the interest of six tomato plants seems like an acceptable trade-off until I learn to make a killer bacon-lettuce-and-elm-seed sandwich. :) Jim@mdc

I liked your story and the peek into practical dendrochronology. I can't help but feel a bit sad that your beautiful elm, which survived development of the area, needed to be sacrificed for a tomato garden.

Hi, Karin. I would imagine that Missouri trees will have very narrow 2011 growth rings on account of last year's drought. In fact, it could be two years in a row. An expert at UMC is predicting another very hot, dry summer. See for details. Jim@mdc

I was just pondering how this past dry dry dry summer (east KS) will appear on the growth rings of the local trees. That weather changes are directly affected by sunspot activity was a bit of a revelation to me, and that scientists use those patterns from throughout history is really remarkable. Thanks for sharing.

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