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Biogeochemical factors contributing to enhanced carbon storage following afforestation of a semi-arid shrubland
1Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, Faculty of Agricultural, Food and Environmental Quality Sciences, the Hebrew University of Jerusalem, Rehovot 76100, Israel
2Department of Environmental Sciences and Energy Research, Weizmann Institute of Science, Rehovot 76100, Israel
Abstract. Ecosystems in dry regions are generally low in productivity and carbon (C) storage. We report, however, large increases in C sequestration following afforestation of a semi-arid shrubland with Pinus halepensis trees. Using C and nitrogen (N) inventories, based in part on site-specific allometric equations, we measured an increase in the standing ecosystem C stock from 2380 g C m−2 in the shrubland to 5840 g C m−2 in the forest after 35 years, with no significant change in N stocks. The total amount of C produced by the forest was estimated as 6250 g C m−2. Carbon sequestration following afforestation was associated with increased N use efficiency as reflected by an overall increase in C/N ratio from 7.6 in the shrubland to 16.6 in the forest. The C accumulation rate in the forest was particularly high for soil organic C (SOC; increase of 1760 g C m−2 or 50 g C m−2 yr−1), which was associated with the following factors: 1) Analysis of a small 13C signal within this pure C3 system combined with size fractionation of soil organic matter indicated a significant addition of new SOC derived from forest vegetation (68% of total forest SOC) and a considerable portion of the old original shrubland SOC (53%) still remaining in the forest. 2) A large part of both new and old SOC appeared to be protected from decomposition as about 60% of SOC under both land-use types were in mineral-associated fractions. 3) A short-term decomposition study indicated decreased decomposition of lower-quality litter and SOC in the forest, based on reduced decay rates of up to 90% for forest compared to shrubland litter. 4) Forest soil included a significant component of live and dead roots. Our results showed the considerable potential for C sequestration, particularly in soils, following afforestation in semi-arid regions, which is particularly relevant in light of persistent predictions of drying trends in the Mediterranean and other regions.
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Citation: Grünzweig, J. M., Gelfand, I., and Yakir, D.: Biogeochemical factors contributing to enhanced carbon storage following afforestation of a semi-arid shrubland, Biogeosciences Discuss., 4, 2111-2145, 2007. Bibtex EndNote Reference Manager
