“Another thing we saw was that while the trees in the high CO2 plots tended to have more leaves and tended to be growing faster, because of their greater leaf area, they dried out the soil faster, so between rainstorms, they went into drought condition earlier and stayed there longer.”
The paper in Ecology Letters emphasized, furthermore, that experiments in other environments had found an even more transitory effect, or none at all. Unfortunately, scientists can’t really say how much of the world’s biomass will fall into each category as the world warms, said Schlesinger, who is now president of the Cary Institute of Ecosystem Studies, an independent nonprofit research center in Millbrook, New York. As far as the fossil carbon being absorbed by forests is concerned, however, “the general feeling now is that while some of that is being driven by a fertilization effect, the bigger effect is actually regrowth of forests on abandoned agricultural land” and other areas where trees have been cleared.
“There aren’t many global greeners running around the way the Idso brothers [Craig and Sherwood] are,” Schlesinger said. “One of them was quoted in that New York Times article. They’ve been saying for years that the CO2 is the best thing for planet Earth—plants will grow abundantly, crops will be overflowing and, you know, it’ll be the Garden of Eden.”
Lamentably, we won’t be getting any more data from Duke’s forest. Its project closed down in 2010; along with a couple other sites, it was part of the Department of Energy-sponsored Free Air Carbon Dioxide Enrichment (FACE) program. Other FACE experiments continue worldwide, however, including one at the Oak Ridge National Laboratory in Tennessee, which drew coverage from the NBC affiliate in Knoxville this summer (unfortunately, rather than explain the work’s import, WBIR-TV pursued an anodyne angle about career development for college students).
Scientists consider the open-air design of FACE projects an improvement upon older, controlled-environment, chamber-based experiments. More research in wider variety of environments to understand what a warmer world will affect forests, however. It would be useful to study carbon enrichment in the tropics, for example, Schlesinger said, but the project are logistically complicated and expensive to run.
Ecologists David Lobell and Christopher Field recently published a paper in Global Change Biology expanding upon the challenges associated with developing good experimental designs for studying the fertilization effect. And for background reading on forests and carbon, it’s worth checking out the publications of Dr. Yiqi Luo at the University of Oklahoma.
These sources contain more details than are likely to find their way into most news stories, but reporters should be bear them in mind for the next time a source tries to tell them that CO2 is just plant food.