Adventures in Tree Measurement

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BY AMERICAN FORESTS BIG TREE PROGRAM COORDINATOR SHERI SHANNON

How do you measure the height of a tree when the view of the canopy is obstructed? This is something I immediately had to learn during a Native Tree Society (NTS) advanced tree measuring workshop at Cook Forest State Park in Pennsylvania with Laser Technology Inc. and NTS measuring masters Bob Leverett and Dale Luthringer.

Trees don't always grow vertically in the middle of an open, flat area where you can easily choose a spot to take measurements. But with the proper equipment, NTS is able to calculate the height of a tree even when the tree's base and top are not aligned - a problem that has caused inaccurate measurements with some other methods. So, how does it work?

Let's first define tree height. Tree height is the vertical distance between the base of the tree and the highest point of the crown. NTS uses two key pieces of equipment to accurately measure height: a clinometer, which is a mechanical device that measures the vertical component of the angle between your eye and a targeted object, and a laser rangefinder, which sends a laser pulse in a narrow beam towards the object and measures the time it takes for the pulse to be reflected off the target and returned to the sender.

On my first attempt at measuring a tree with this advanced method, I immediately look up into the crown of a pine and think, "With a push of a button - in seconds - I'll have the number I'm looking for on the screen of my laser rangefinder." Well, there were some numbers, but they definitely weren't what I was looking for. I had to move around for about 10 minutes to find an open area to get the best view of the crown. That's when I realized that even with the best equipment, it takes time to measure a tree.

Before I know it, I'm standing in the presence of the tallest tree north of the Great Smoky Mountains: Longfellow Pine. It's my turn to take the challenge and measure the height of this champion, but how am I supposed to go about doing that when the pine sits on a steep slope? Everyone disperses in different directions while I just focus on not falling and twisting an ankle as I climb over fallen branches and rocks to find the best view of the crown. …