Globally, forests and their soils account for about twice as much carbon as is present in the atmosphere, and hence the response of forests to increasing atmospheric CO_2 is expected to be an important component of the global carbon cycle. However, compared to what is known from studies of small trees and herbaceous vegetation, in which elevated CO_2 has been shown to have a fertilizing effect on growth, there has been relatively little experimental research on mature forest stands. Using a 45-m canopy crane in a 100-year-old mixed deciduous forest in Switzerland, Bader et al. exposed tree crowns to 550 ppm CO_2 over 8 years and compared the ecosystem's response to that of control trees not exposed to elevated CO_2.
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