Climate Science

An Off-Season Carbon Sink

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Science  23 May 2003:
Vol. 300, Issue 5623, pp. 1205
DOI: 10.1126/science.300.5623.1205c

In most plant species, the efficiency of water use during photosynthesis is increased by higher CO2 concentrations. Therefore, elevated atmospheric CO2 concentrations (from the burning of fossil fuels) would permit afforestation in drier regions. Drylands occupy vast areas of the globe, and greater forest cover would presumably increase carbon sequestration as well as provide a natural resource for local populations. In order to determine whether such an opportunity might exist, Grünzweig et al. conducted eddy flux, physiological, and inventory measurements in a 35-year-old forest (2800 hectares) at the edge of the Negev desert and evaluated the carbon balance of this system. The dryland forest stores 6.5 kg of C m−2 and accumulates 0.13 to 0.24 of kg C m−2 yearly. The uptake of CO2 is highest during the winter, which is out of phase with most Northern Hemisphere forest activity and would expose low-latitude forests to CO2 concentrations ∼10 ppm higher than those in the summer. Expanding such afforestation efforts into regions of sparse shrubs and C4 grasses could lead to significant carbon sequestration.—HJS

Global Change Biol. 9, 791 (2003).

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