Tree Stories: How Tree Rings Reveal Extreme Weather Cycles

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When you look at a forest in Utah, whether from an airplane or hiking around, you might not realize that there's a library of information in those trees. Each tree is recording information about the environment that it's growing in. The main focus of my work right now is to try to reconstruct stream flow from tree rings. The process is dendrochronology, so "dendro" for tree and "chronology" for time. We primarily take very small core samples about the diameter of a pencil with a handrill and then we take it back to the lab. By cross stating the rings in this dead tree with living trees, we'll be able to identify when this tree died. Then we follow that up by measuring the rings a thousandth of a millimeter, so its very detailed work. When we have droughts, the rings are very narrow and the more extreme, the narrower the ring.

As we're trying to identify patterns in wide and narrow rings, you can kinda think of that as a barcode in the food that you might buy in the store. Trees in an area are going to have not exactly the same pattern, but a similar pattern of wide and narrow rings, just like a barcode. We get to the point where we can just look across the sample and say "Okay, there's 1580 and there's 1735." We know where those difficult years are. We're able to look at the records in the rings and from that reconstruct streamflow much further back than we can just with historical records. In some areas under the best conditions with the best species, we can have up to a 10,000 year record from tree rings. We have maybe 50 to 100 years of historical records for the rivers around here, but we have trees that can go back several hundred years. If you look at the Weaver river, we have about a hundred years of records. So that gives us a rough idea of how long droughts have been and how severe they been, but it's only 100 years of records. And the trees have been around for six or seven hundred or more years and they can give us a much longer record of those droughts.

Sometimes as we look in the tree rings, we see droughts there much longer and much more severe than anything we've seen the historical record We've had routes that have lasted for more than a decade. We've had one that lasted for sixteen years. Water managers can actually incorporate those in the forecast models to help us better prepare for droughts in the future. We're excited to be able to take the information and give that to water managers now because they haven't had that for the Wasatch Front before..

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