The Changing Atmosphere Could Drive Forests to Use More Water


Fossil fuel use is causing an increase in the atmospheric concentrations of both carbon dioxide and ozone. In principle, an increase in the concentration of either gas can reduce the amount of water used by plants in transpiration (evaporation of water from plants), but a group of SC-sponsored scientists recently discovered that this was not the case in a unique and large-scale field experiment. The scientists directly measured effects of elevated carbon dioxide and ozone concentrations on forest-tree transpiration in the SC Program for Ecosystem Research’s ecosystem-scale elevated-carbon-dioxide and elevated-ozone field experiment in northern Wisconsin forest stands (the world’s largest long-term study of ecological effects of changes in atmospheric composition). They found that increasing the concentration of the gases 40-50% above ambient concentrations caused an increase in transpiration of about 14%. The results indicate that, if other factors remain constant, increasing atmospheric concentrations of carbon dioxide and ozone might cause an increase in water use by temperate forests. These findings alter our basic understanding of interactions between atmospheric composition and water cycling in forests. The research was recently reported in the journal Tree Physiology.