Coring Trees

This is not how you actually hold a corer – I was too busy posing to keep my hands in the proper position! You’re supposed to have one facing up, one facing down.

My hydrology class went out coring trees to study dendrochronology! Dendrochronology is the study of trees through time . To take a core sample, you gently screw this hollow tube into the tree, and then insert an extractor that much resembles a long-handled ice tea spoon, which grips onto the end of the core and pulls it out.

Much as it seems really invasive, they’ve apparently figured out a way that this doesn’t harm the tree. I like to think of it like getting an ear piercing with a hollow needle, or a biopsy.

Then we let the cores dry out in the lab, and our professor used a planer saw to flatten them out. Then the real work of counting and measuring rings began!

The youngest rings are the smallest, because a tree grows from the inside-out. When the tree has grown larger, the total growth for the tree is spread out over a larger area – this results in smaller rings. In addition to marking the years on the core-holder, you also mark the core with a certain number of dots – one for a decade, two for a half-century, three for a century, etc..

Once you get close to the tree’s center, the rings become much larger. In this picture, you can see how the rings near 1810 are curving, instead of being perpendicular to the core – this means that we missed the core. These rings aren’t very useful to measure, because it’s difficult to get a good reading on their actual width.

We correlated this data with historical precipitation data, to see how the growth reacted to precipitation. Our correlation was quite poor, since our measuring tools were fairly low-grade. (Plus, we’re newbs.) But, with the proper measuring tools, many more data points, and a lot more practice, a good correlation can be established. The relationship from this correlation can then be used as a proxy to establish possible precipitation values for the years before historical measurements exist. In addition to being a useful tool for looking at a particular region’s specific precipitation and plant growth patterns, this is one of the primary methods current climate change studies rely upon to establish past climate figures.