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GUY RAZ, host:

About an hour east of Washington, D.C., in a forest along the banks of the Chesapeake Bay in Maryland, the trees are, all of a sudden, growing faster, much faster than ever before, in some parts, twice as fast. And scientists now believe they've figured out the mystery.

This is a pretty typical mid-Atlantic forest: oaks, hickory trees, tall tulip poplars that grow straight up like Roman columns.

(Soundbite of bell)

RAZ: And to get there, you have to drive past a security guard and down a winding road.

Dr. GEOFFREY PARKER (Ecologist, Smithsonian Environmental Research Center): So, welcome to SERC. I guess you've never been out here before.

RAZ: That's our guide, the ecologist Jess Parker, and on a recent morning, he took us deep inside the forest on the grounds of the Smithsonian Institution's Environmental Research Center.

Dr. PARKER: I leave the keys here, okay? Just so you know.

RAZ: There are thousands of trees here, and every single one is mapped. Parker literally carries that map, with thousands of colored dots on it, and he leads us into a part of the forest where a group of volunteers and researchers is taking measurements.

Unidentified Man: 8.5.

Unidentified Woman 8.5. Okay, and the number?

Unidentified Man: 070610.

Unidentified Woman: 070610, got it.

RAZ: Some of the trees here are 300 years old, and each one, each poplar or oak or hickory tree, is tagged with an ID number. Around some of them is a thin band made from metal. It's called a dendrometer, and it's used to measure the tree's circumference. And almost every single day since he started working in this forest more than 20 years ago, Jess Parker has monitored these trees.

You came here the first day, and you said, I need to measure trees.

Dr. PARKER: Yes, you might as well get started.

RAZ: And recently, he decided to gather up all that data he has collected over those 20-plus years - the measurements, the changes in temperature and carbon levels - and crunch the numbers, and he noticed something astonishing.

Dr. PARKER: In taking all the data from these different plots of different ages, we assembled the general pattern of how forests around here grow, but when we looked on that graph of what individual plots were doing, such as this one right here, we discovered that it was growing at a much higher rate than you would expect for a forest of its age. So this 130-year-old forest here is growing faster than one would expect from that general pattern.

RAZ: How much faster?

Dr. PARKER: Well, we put this usually in metric terms, on the order of three metric tons of biomass per hectare per year, and in some cases, that's double. In some cases, it's just an extra 50 percent. And the pattern that we see, we believe, is relatively recent.

RAZ: And Jess Parker believes the forests are growing faster because of climate change.

Dr. PARKER: Over the 23-year period that we've done this project, the average temperature has gone up by about three-tenths of a degree C.

RAZ: In this forest?

Dr. PARKER: Yes, and in the region in general. The length of the growing season, as defined from the time of the last frost in the spring to the first frost in the fall, has increased by about a week. And the CO2 level in the atmosphere has gone up by about 12 percent.

Now, each of those effects is known to be able to stimulate the growth of trees, and so it's not at all unlikely that brought together, all three of those could've been involved in the extra growth that we're seeing.

RAZ: Can you explain how an increase in carbon contributes to more rapid growth of a forest?

Dr. PARKER: Well, we know that in experimental settings, when you fertilize the atmosphere around plants with extra CO2, they grow faster.

RAZ: So it acts like a fertilizer.

Dr. PARKER: In a sense, yes.

RAZ: Is this something localized here in the mid-Atlantic or even along the Eastern Seaboard, or do you know if this phenomenon is happening somewhere else around the world?

Dr. PARKER: There have been numerous reports in the literature of extra growth in forests throughout the world.

RAZ: What kind of consequences would there be for weather patterns in the area?

Dr. PARKER: If the trees are growing faster and longer, they're probably also transpiring water more. Extra water vapor in the atmosphere can affect the amount of cloudiness, and that can affect the heat balance of the lower atmosphere. I'm not sure how that will translate into the local weather here in the D.C. area, but it's likely to have a large-scale effect.

RAZ: So could it mean more extreme weather like the snowstorms we experienced here in Washington, D.C., this past winter? Scientists don't know, and as Jess Parker led us back out of the forest, he said it's probably too early to know anyway.

Are you worried about this?

Dr. PARKER: About what?

RAZ: What's happening here?

Dr. PARKER: No, I'm just amazed by it. We discovered this in our data a year or so ago.

RAZ: I mean, you're not alarmed by it?

Dr. PARKER: No, I guess I'm personally not alarmed. I'm very curious about the whole thing, what's causing it, how far it can go on and what its other effects might be, but alarmed, I wouldn't say so.

RAZ: To see photographs of the forest and to find a link to Jess Parker's study, visit our Web site, npr.org.

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