Last month, I spent several days in Harvard Forest, 3500 acres of woods dedicated to scientific research. The forest is home to dozens of research projects, some short-term, others stretching over decades.Read the rest
Scientists measure trees for a wide variety of reasons. When I visited the Harvard Forest last week, I measured them as part of studying carbon sequestration by plants. But you can't just go out into the woods with any old tape measure and expect to collect some significant data.
That's because where you measure the tree matters. If you want to compare the diameters of two trees, you have to make sure you're measuring them in the same place. If you measured one tree at the wide base and the other further up the trunk, where trees usually get narrower, the comparison wouldn't mean much.
That's where diameter breast height (DBH) comes in. It's a way of standardizing the measuring process.
As the name implies, DBH is meant to be a diameter measurement of a tree trunk taken at, roughly, breast height on an adult. Of course, where exactly "adult breast height" is varies greatly from person to person. So DBH has been set to a standard height—1.4 meters in the United States.
In a research forest, you'll often see some kind of marker on the trees showing where this official "breast hight" is, so people can quickly move through the woods, taking diameter measurements, without having to measure vertically on each tree. In some cases, DBH is marked with yellow spray paint. In others, metal bands. These metal bands actually help measure diameter, too. Set with springs, the bands expand as the tree does, so all researchers have to is measure the distance between two dots on the band and see how far apart the dots have moved since last time.
Earlier this week, I showed you how scientists can use a simple, hand-operated tool to collect stratified core samples of mud at the bottom of a swamp. The deeper the samples go down, the older the mud is—until, eventually, you're looking at 6000-year-old muck, the remains of a lake bed that filled in with sediment and became swamp.
The core samples are narrow logs, each 50 cm long. (In all honesty, they looked like less-colorful versions of the 3 pound gummi worm I ordered for my 30th birthday party last year.) For the most part, they're some variation on the shade of brown, with occasional streaks of red and burnt umber, until you get to the very bottom. There, the samples turn grey. Put a bit in your mouth, as I was encouraged to do by Harvard Forest director David Foster, and you'll taste clay and feel grit between your teeth.
That's all well and good. But what do you do with core samples once you have them? For this installment of Dispatches From Harvard Forest I'm going to leave the woods and head into the lab, to see what happens to the parts of the Forest that scientists take home.
Step one: Make dirt cupcakes
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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?
I spent last weekend in the Harvard Forest, participating in hands-on science experiments as part of the Marine Biological Laboratory's science journalism fellowship. The goal was to give us an inside look at what, exactly, scientists actually do. When you're reading a peer-reviewed scientific research paper, where did all that data come from?
Sometimes, it comes from a swamp.
On Saturday, we walked into the Forest's Blackgum Swamp to take core samples out of the muck. There was no standing water in this swamp, at least not when we visited. But I wouldn't call the ground "solid", either. Instead, it was more like a moss-covered sponge. With every step, the ground beneath me would sink and smoosh. In some of the lower patches, that meant a shoe-full of water. In other spots, it was just a disconcerting sensation.
Taking core samples involves a little machine that's like a cross between a shovel and a straw. Made of heavy, solid metal, it has an extendable handle on one end. At the other, there's a hollow, cylindrical chamber that can be opened and closed by turning the handle counterclockwise. You drive the chamber into the ground, turn the handle, and then pull it back out. Once everything is back on the surface, you can open the chamber and see a perfect cylinder of earth, pulled up from below. That cylinder is removed from the chamber, wrapped in plastic wrap, labeled, and put in a long wooden box. Then you do all of that again, in 50 centimeter increments, until you hit stone. We got to about 475 centimeters—15 feet deep. By that point, you'll have collected 1000s of years of layered sediment.
This is not as easy as it sounds.
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I'm currently attending the Marine Biological Laboratory's 10-day science journalism fellowship. As part of that, I get to do some hands-on science experiments and get a better perspective on how the work of science is done and how data is collected.Read the rest
Do you see how the ground level is higher on the left-hand side of this photo? To the right of the stone wall, the ground distinctly drops by a foot or more.
That wall is more than 200 years old. It marks the border between what was once a plowed field (on the left) and grazing pasture (on the right). Today, this site is woodland—part of the Harvard Forest, the most-studied forest in the world. But for generations, this land was farmed by Jonathan Sanderson and his descendants. And, even two centuries later, you can still see the way different uses of the land changed the land.
For instance, the ground level is higher on the left because plowed fields erode more easily. This site is on a slight slope. Water runs downhill, toward the right hand corner of the photo. As it did that, it carried bits of plowed field along with it—sediment that washed up against the stone wall and stayed there. Over many years, the effect changed the level of the land.
This isn't necessarily a catastrophic thing. But it is change. I spent last weekend in the Harvard Forest, participating in science in a hands-on way as part of the Marine Biological Laboratory's science journalism fellowship. One of the things I learned during my stint in the forest: The past ain't past. History is recorded in geology and ecology as surely as it's recorded in books. Very cool stuff!
I spent Friday, Saturday, and Sunday in the Harvard Forest—the most-studied forest in the world. It's an interesting place, with a complicated history. Originally forest, it was clear-cut in the decades following European settlement. By 1830, less than 90% of this part of Massachusetts had any forest left. But that trend had already begun to reverse itself by 1850, spurred by urbanization and cheaper, more-efficient farming in the "West" (i.e., Ohio).
What is now the Harvard Forest was farmland for many years. Then it was used for tree plantations. Then it became forest again, studied first by Harvard University's forestry program in the early 20th century, and then by ecologists and other environmental scientists beginning in the 1980s. Today, these 3,500 acres are home to dozens of individual studies and long-term, interdisciplinary projects led by scientists from more than 15 universities and institutions.
This particular study, led by Dr. Jerry Melillo of the Marine Biological Laboratory, is studying the nitrogen and carbon cycles of forests, and how those cycles are affected by rising soil temperatures. They're trying to understand how climate change will affect the growth of wild plants, and how it will affect those plants' ability to absorb and store carbon dioxide. I'll get more in-depth on this study later. Right now, I thought that this site offered a really great view of what a research forest looks like—it's a chance to see detail-oriented science and wild nature interacting and overlapping.