Effects of Atmospheric CO2 Enrichment on Forest Water Use
Warren, J.M., Potzelsberger, E., Wullschleger, S.D., Thornton, P.E., Hasenauer, H. and Norby, R.J. 2011. Ecohydrologic impact of reduced stomatal conductance in forests exposed to elevated CO2. Ecohydrology 4: 196-210.
Building upon this historical foundation, Warren et al. used "a combination of measurements, synthesis of existing literature, and modeling to address the consequences of climate change on ecohydrologic processes in forests, especially [their] response to elevated CO2 (eCO2)," employing data that had been obtained from five free-air CO2 enrichment or FACE studies that had been conducted in temperate forest ecosystems.
The six scientists report that at two of the FACE sites, where the studied forests "were in the early stages of stand development," there was "a strong eCO2-stimulation of canopy leaf area [that] led to enhanced stand water use." In the three closed-canopy forests, on the other hand, they say that "eCO2-reduced stomatal conductance led to declines in canopy transpiration and stand water use." In the sweetgum FACE experiment conducted in Oak Ridge, Tennessee (USA), where most of their work was conducted, for example, they found that eCO2 reduced seasonal transpiration by 10-16%.
Warren et al. conclude that "the direct effect of eCO2 on forest water balance through reductions in transpiration could be considerable, especially following canopy closure and development of maximal leaf area index," noting that in the case of temperate deciduous forests, "reductions in canopy transpiration and stand water use due to direct effects of CO2 on stomatal conductance will be reflected in increased soil water content and potential water yield," which should result in significant contributions to groundwater, streams, lakes and rivers.
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