Such economic incentives are provided under so-called "carbon trading exchanges" encouraged by the Kyoto Protocol and the European Union's Greenhouse Gas Emission Trading Scheme, the study noted.
Co-authors Roni Avissar, a professor of civil and environmental engineering at Duke's Pratt School of Engineering, and his postdoctoral research associate Somnath Baidya Roy then used computer climate models of their own design to simulate how added forest moisture might affect climates in those regions.
"While a weather forecaster makes predictions about the weather for the next day or week, we instead forecast climate given other kinds of scenarios, such as changes in land use," Roy said.
Those simulations showed no evidence that such significant land conversions could help generate more rainfall except perhaps in northern Florida and southern Georgia. In general, "unlike in the tropics, the temperate regions modeled here did not have sufficient energy to lift the additional atmospheric moisture high enough to condense and form clouds," the study said.
"Plantations not only have greater water demands than grasslands, shrublands or croplands," the study added. "They typically have increased nutrient demands as well."
In order to store carbon from carbon dioxide in their tissues, trees must also remove nutrients like calcium and potassium and nitrogen from the soil, Jackson explained. During these chemical exchanges, "you leave sodium behind, which builds up in the soil to make it saltier," he said.
Jackson's former postdoctoral scientist Esteban Jobbgy, now at the Universidad Nacional de San Luis in Argentina, and Kathleen Farley of The Nature Conservancy, also investigated another way that forest growing might increase soil salinity in Argentina's normally treeless pampas.