Trees That Love Global Warming

Every day an 18-wheel tanker truck pulls up alongside a lush forest near Duke University in North Carolina. Within a short time, the truck’s cargo of dreaded carbon dioxide gas begins flowing through a series of pipes and onto a forest rich with loblolly pines and small hardwood trees.

For four years now, scientists at Duke have inundated the forest with carbon dioxide, the principle greenhouse gas that is expected to wreak havoc on the planet in the decades ahead by elevating temperatures, causing sea level to rise, and severely altering vegetation around the globe.

Why, one might ask, would these good people deliberately subject the forest to such harsh treatment?

The goal of the project is to replace theory and conjecture with hard facts about the impact of increased levels of carbon dioxide, produced primarily by the burning of fossil fuels. Those facts are hard to come by, because the effect will be decades long, and it’s not easy to nail down evidence in such a complex arena. So the Duke researchers are addressing one fundamental question: What effect will elevated levels of carbon dioxide have on plant life?

Pines Thrive

The preliminary answer seems to be that at least some of the trees in the forests will love it, growing more rapidly, reproducing more robustly, thriving at a time when some parts of the globe will slip perilously into a rising sea.

“It’s really dramatic,” says Shannon LaDeau, a doctoral candidate at Duke who is running part of the long-term experiment.

The pines are growing about 25 percent faster than pines just outside the experiment, and they are twice as likely to be reproductively active. “They are making three times as many cones” which carry and incubate their seeds, she adds.

So if the trees there are doing so well, why is the world in an uproar over global warming? Because the Duke experiment addresses only one part of a problem that is extremely complicated.

What’s good for the loblollies is devastating to other living organisms, including coral reefs. Researchers at Columbia University’s Biosphere 2 in the Arizona desert have found that the atmospheric level of carbon dioxide that we might expect in a few decades will dissolve the reefs like an ice cube in boiling water.

So we can expect some good and some bad effects from global warming. Arid regions that lack water for agriculture may get a lot more rain, but low-lying regions will most likely slip below sea level.

And the forests, while robust in some areas, will almost surely change.

“You’re certainly going to change the competitive dynamics between different species,” LaDeau says.

“We could have a change in forest composition, dominated by those species that can use carbon dioxide efficiently at the expense of others,” adds William H. Schlesinger, professor of botany and the principal investigator on the project.

Localized Greenhouse Effect

The Duke experiment is an interesting marriage of technology and science. The carbon dioxide is pumped into a series of pipes surrounding a plot of land about 90 feet in diameter.

“These are big pipes that extend above the canopy of the pine forest,” LaDeau says. The level of carbon dioxide is continuously monitored. When the level drops, the system delivers more gas, and if it rises too high, it simply shuts down.

“If the wind comes out of the west, it turns on the pipes on the west side,” she adds, keeping the level precisely the same, even on a windy day.

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