Trees are living records of Earth’s climatic past. Play NOVA’s Polar Lab to learn how trees grow by simulating how they respond to different environments
Why Trees Are Living Climate Records
Published: February 25, 2020
Caitlin Saks: When a tree grows, it encodes information into its wood, kind of like a living book.
Each year, a tree grows thicker by adding a layer of new wood. So if you slice through the trunk and look at these layers, which appear as rings, you’re looking at a record of how that tree grew, year after year.
Let’s take a closer look at how the rings form. Under a microscope, you can actually see the individual cells. During the growing season, the new cells are large, and thin-walled. We call this “early wood,” and it forms the lighter part of the ring. Then as the days become shorter, the tree starts to prepare for winter by producing cells that are smaller and thicker-walled. And we call this “late wood,” and it forms the darker part of the ring. In winter, the tree stops growing altogether and stays dormant until spring. But that’s not all.
The tree rings can actually tell us something about the environment that the tree was growing in. When conditions are favorable, the tree rings are fatter. And when resources like water and the sun’s energy are scarce, they’re thinner. What that means is that really old trees can actually tell us something about what the climate was like even before humans had records.
Hosted by: Caitlin Saks
Production by: Ari Daniel & Lorena Lyon
Camera: Emily Zendt
NOVA Labs Editorial Director: David Condon
Visuals: Jim Basinger, Fritz Schweingruber | WSL, TREX | Nicole Davi, Videoblocks, Wikimedia Commons | Josef Reischig
© WGBH Educational Foundation 2020