Carbon sequestration in arid-land forest

Rising atmospheric CO2 concentrations may lead to increased water availability because the water use efficiency of photosynthesis (WUE) increases with CO2 in most plant species. This should allow the extension of afforestation activities into drier regions. Using eddy flux, physiological and inventory measurements we provide the first quantitative information on such potential from a 35-year old afforestation system of Aleppo pine (Pinus halepensis Mill.) at the edge of the Negev desert. This 2800 ha arid-land forest contains 6.5 +/- 1.2 kg C m(-2) , and continues to accumulate 0.13-0.24 kg C m(-2) yr(-1) . The CO2 uptake is highest during the winter, out of phase with most northern hemispheric forest activity. This seasonal offset offers low latitude forests similar to10 ppm higher CO2 concentrations than that available to higher latitude forests during the productive season, in addition to the 30% increase in mean atmospheric CO2 concentrations since the 1850s. Expanding afforestation efforts into drier regions may be significant for C sequestration and associated benefits (restoration of degraded land, reducing runoff, erosion and soil compaction, improving wildlife) because of the large spatial scale of the regions potentially involved (ca. 2 x 10(9) ha of global shrub-land and C4 grassland). Quantitative information on forest activities under dry conditions may also become relevant to regions predicted to undergo increasing aridity.