Changing Water Balance in Forests Exposed to Elevated CO2


Plants influence ecosystem water balance through responses to environmental conditions, and their sensitivity to climate change could alter the ecohydrology of future forests. DOE scientists at Oak Ridge National Laboratory used a combination of measurements, synthesis of existing literature, and modeling to study the consequences of elevated CO2 on ecohydrologic processes in forests. Data from five of DOE’s free-air CO2 enrichment (FACE) sites reveal that elevated CO2 reduced the passage of water vapor through the stomata, or small pores of the plant, leading to declines in canopy transpiration and water use for three closed-canopy forest sites. At the sweetgum FACE experiment in Oak Ridge, Tennessee, elevated CO2 reduced seasonal transpiration by 10–16%. Model simulations also predicted reduced demand for water in response to elevated CO2. The direct effect of elevated CO2 on forest water balance through reductions in transpiration could be considerable, especially following canopy closure and development of maximal leaf area index. Complementary, indirect effects of elevated CO2 include potential increases in root or leaf litter and soil organic matter, shifts in root distribution and altered patterns of water extraction.


Warren, J. M., E. Pötzelsberger, S. D. Wullschleger, P. E. Thornton, H. Hasenauer, and R. J. Norby. 2011. “Ecohydrologic Impact of Reduced Stomatal Conductance in Forests Exposed to Elevated CO2,” Ecohydrology 4, 196–210. DOI: 10.1002/eco.173.