Trees That Love Global Warming

Schlesinger says he wasn’t surprised that the trees in the plots grew dramatically during the first year of the experiment, 1996, because trees absorb carbon dioxide through photosynthesis. But the trees continued to grow about 25 percent faster than trees outside the plots over a three-year period, and that, he says, was surprising.

“Basically, the trees woke up one day to 560 parts per million carbon dioxide, and that was essentially newfound wealth in terms of photosynthesis, but you can’t sustain that rate in photosynthesis in greenhouse experiments without adding fertilizer,” Schlesinger says.

He added that they did not add fertilizer to the soil and it’s still too early to tell if that growth rate will be sustained through the current year, the fourth year of the project.

One unintended result of the research was to fuel the vigorous political debate over global warming. Some scientists argue that the dire predictions will never come true, partly because forests will expand rapidly and absorb any significant increases in carbon dioxide.

Good for Some, Bad for Most

“Our calculations suggest there will be some of that, but at the very most we can only get half the emissions of carbon dioxide from fuels into the forests,” Schlesinger says. “The other half would accumulate in the atmosphere and lead to global warming.”

He also points out that loblolly pines are not typical. They are among the fastest growing trees on the planet, and as the Duke experiment reveals, they are very responsive to elevated levels of carbon dioxide. So it would be a terrible mistake, he says, to extrapolate from the Duke experiment and conclude that nature will heal this wound.

The impact of carbon dioxide on plant life is just beginning to be understood. A similar project in Tennessee has found that hardwoods also experienced a 25 percent jump in their growth rate during the first year, but that is a very young experiment and it remains to be seen whether that growth will be sustained.

Young hardwoods, mostly oak and hickory, near the base of the loblolly pines in the Duke experiment are also growing rapidly. They should take over the forest in about 50 or 60 years, Schlesinger says, smothering out the loblollies. Unless, of course, the pines win that battle by sucking up enough carbon dioxide to beat out the competition. That’s the sort of thing ecologists worry about, because it could upset the balance of nature that allows many other creatures to survive.

No matter how it pans out, Schlesinger says, the forest of the future will probably look much different than it does today.

“There will be a different composition, and the diversity may be lower,” he says. But there’s one thing he’s pretty sure of. Some of those trees are going to grow like crazy.

Lee Dye’s column appears weekly on A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.

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