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The Secrets of Tree Rings

The Secrets of Tree Rings
A portion of a black walnut tree core as seen through the lens of a microscope

I’ve spent the a majority of my time since my last blog peering down a microscope at tree rings, so I figured now was as good a time as any to share what I’ve learned.

For starters, trees grow out, not up. A branch that was five feet off the ground in 1998 will still be five feet off the ground tomorrow. Furthermore, trees grow from the outside, laying down layers of new wood just underneath the bark; rather than from the center. Especially in places like the midwest that have distinct seasons, trees alternate between periods of growth in the summer and dormancy in the winter. The harsh lines formed between growing seasons are what cause the visual rings.

Since trees create a new ring every year, by counting backwards from the bark you can determine how old a tree is! I wouldn’t be surprised if many of you already knew this, but this isn’t all tree rings can tell us.

The width of a tree ring can also tell us a lot about how the tree grew in that particular year. Large rings mean that tree was able to grow a lot; this could mean lots of sunlight, copious amounts of rain, or appropriate pruning. Similarly, small rings are from years that the tree didn’t do as well, often from injury or lack of rain. Most of the trees I’ve measured have had distinctly small rings in 2012 due to the drought.

Thus, tree rings allow scientists to look into the history of both a tree and it’s environment. In my particular case, I’m comparing the tree rings of trees from parts of the forest under different prescribed burning treatments in order to see if the varying fire regimes have any effect on tree growth. Fire is an important management tool in midwest oak forests so I’m excited to know if it is actually as good for the trees as we think is.


About the Author
My name is Sierra Lopezalles. I am a rising sophomore at the California Institute of Technology double majoring in Biology and History. I am a 2017 summer undergraduate research intern at The Morton Arboretum working in the forest ecology lab with Dr. Christy Rollinson. My project is to study how different regimes of prescribed burning effects the mature trees of the Morton East Woods.