Uncovering the Secrets of Forest Canopies

Uncovering the Secrets of Forest Canopies

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On SERC's 2,800 acres, besides its fine range of forests young and old, are salt marshes, a freshwater marsh, cornfields, winter cover crops and newly abandoned fields.

"The problem with studying a forest canopy," Parker observes, "is that it's a giant pain to get to. We sometimes climb trees."

The trouble with having to climb, though, is that researchers can only get, say, 80 percent of the way to the top, and the action is at the top 20 percent of the canopy. That's where the light is, where photosynthesis and production take place, where leaves have the highest nutrient content, where carbon dioxide is taken up and water vapor is released, and where the wind decelerates the most dramatically.

"There are other ways to get into the canopy. We can rent a crane, which allows us to come in from above, from the point of view of the atmosphere," he tells me. "When you go up on a tower crane with a video camera, the world is so different from life on the forest floor. It changes your way of thinking."

But a crane is expensive. Another solution is to build a tower. This only gives you a view of one place, and besides, it makes a hole of its own in the forest, skewing some observations. There are various optical techniques for measuring canopies, including a laser that provides a sample of light reflection. And then there are the balloons. These refrigerator-size helium bags were invented by George Rasberry. They can take light sensors and measuring devices up into the trees and reach all sorts of odd places. They also can be raised gradually to take measurements from the ground up to the top of the canopy. And they are cheap.

"Another thing we study is the bumpiness of a forest," Parker tells me. "Not roughness but rugosity, corrugation. A young forest can be very dark, compact, because its growth has been efficient. As the canopy gets taller, the leaves spread out and more light comes in. Some trees die, leaving gaps. New trees grow in, mostly species that thrive in dark places, and gradually the forest becomes more complex, bumpier, with more variations. Assessing a forest's bumpiness is a quick, cheap way to learn what's going on inside," he says.

A laser technique for measuring the bumpiness of canopies also came out of SERC's studies here in Edgewater, one of many SERC contributions to the science of canopies. These studies are becoming steadily more important as people try to manage such things as atmospheric gases and species diversity.

"If a city manager's concern is how to take up greenhouse gases like carbon dioxide, for example, I can advise him to conserve younger forests, which have a higher uptake of CO2. If his concern is species diversity, however, I would recommend conserving older forests. This whole thing feeds quickly into the question of land management," explains Parker.

The main forest that Parker studies was a pasture 110 years ago. (The SERC buildings stand close by on a former dairy farm.) It is 130 feet tall, with 31 species of trees up to eight inches in diameter. "At 110 years old," he says, "this forest is just postadolescent. It's still vigorous, still putting on more carbon than it gives off. This is my lab."

It is here that his staff measures the trees and calculates their ages, studies the structure of the canopy and analyzes the effects of pollution and other variables.


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