Seventy-one feet above the Harvard Forest, you can stand on a plywood platform attached to a slightly swaying tower of metal scaffolding, and look out over miles of hemlock groves. On the ground, the trees are massive—trunks reaching up and up and up. From the top of the tower, though, the view feels a bit like hanging out in a Christmas Tree farm. All you see are the friendly, conical tops.

The Hemlock Eddy Flux Tower is one of four research towers in the Harvard Forest. Since 2001, data collection systems on the top of this tower have measured carbon dioxide, water vapor, and wind currents. These measurements are made five times every second.

Thanks to this system, we now know that even a relatively old forest like this can still capture and store a decent amount of carbon dioxide. The hemlocks around the tower are pushing 230. That's not terribly old by tree standards, but it's old for this part of North America—most of which was once clear cut. It's also old enough to challenge some previously held conventional wisdom about what kinds of forests are best for carbon sequestration. Previously, scientists thought only young forests, where the trees were still growing rapidly, did that job very well. Sites like the Hemlock Tower have shown a different story.

Also: It's rather terrifying to climb. The tower lives, it is not stationary. A network of steel cables keep it from toppling over, but you can still feel it tilting one way and then the other underneath you. And, at every landing on the stairs, there's a precarious little gap you have to step over. I took my camera with me in one hand as I made the ascent. About partway up, the filming quality takes a notable turn for the worse as I found myself clinging a bit more tightly to the hand rails. How's that for an awesome tool of science?

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