Global greenhouse gas implications of land conversion to biofuel crop cultivation in arid and semi-arid lands – Lessons learned from Jatropha |
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| Institution: | 1. Department of Soil and Geological Sciences, Sokoine University of Agriculture, P.O. Box 3008, Morogoro, Tanzania;2. World Agroforestry Centre (ICRAF), P.O. Box 30677, Nairobi, Kenya;3. Tanzanian Soil Information Service (TANSIS), Seliani Agricultural Research Institute, P.O. Box 6024, Arusha, Tanzania;4. Mlingano Agricultural Research Institute, P.O. Box 5088, Tanga, Tanzania;5. Department of Agricultural Engineering and Land Planning, Sokoine University of Agriculture, P.O. Box 3003, Chuo Kikuu, Morogoro, Tanzania;6. Department of Earth and Environmental Sciences, University of Leuven, Celestijnenlaan 200E, Leuven, Belgium;7. Selian Agriculture Research Institute (SARI), Arusha, Tanzania;8. Lushoto District Council, Lushoto, Tanzania;9. Department of Soil, Water and Climate, University of Minnesota-Twin Cities, 1991 Upper Buford Circle, Saint Paul, MN 55108, United States;1. Centre for Rural Development, Humboldt Universität zu Berlin, Hessische str. 1-2, 10115 Berlin, Germany;2. Department of Crops, Horticulture, and Soils, Egerton University, P.O. Box 536, Egerton, Kenya;3. Potsdam Institute of Climate Impact Research (PIK), P.O. Box 601203, 14412 Potsdam, Germany;4. Department of Sustainable Land Use and Climate Change, Faculty of Life Sciences, Humboldt Universität zu Berlin, Germany;5. World Agroforestry Centre (ICRAF), United Nations Avenue, Gigiri, P.O. Box 30677-00100 GPO, Nairobi, Kenya;6. CGIAR Research Program on Climate Change, Agriculture, and Food Security, United Nations Avenue, Gigiri, P.O. Box 30677-00100 GPO, Nairobi, Kenya;7. World Agroforestry Centre (ICRAF), Avenue des cliniques No 13, c/o INERA, Kinshasa, Congo;1. Institute of Agricultural Sciences in the Tropics (Hans-Ruthenberg-Institute), University of Hohenheim, Garbenstrasse 13, 70599 Stuttgart, Germany;2. Institute of Physicochemical and Biological Problems in Soil Science, Russian Academy of Sciences, 142290 Pushchino, Russia;3. Center for Mountain Ecosystem Studies, Kunming Institute of Botany, Chinese Academy of Sciences, Heilongtan, Lanhei Road 132, 650201 Kunming, China;4. Key Laboratory of Economic Plants and Biotechnology, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, China;5. World Agroforestry Centre (ICRAF), China, East Asia Office c.o. Kunming Institute of Botany, Heilongtan, Lanhei Road No. 132, Kunming 650201, China;1. International Center for Tropical Agriculture (CIAT), Nairobi, Kenya;2. World Agroforestry Centre (ICRAF), Nairobi, Kenya;3. International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria |
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| Abstract: | Biofuels are considered as a climate-friendly energy alternative. However, their environmental sustainability is increasingly debated because of land competition with food production, negative carbon balances and impacts on biodiversity. Arid and semi-arid lands have been proposed as a more sustainable alternative without such impacts. In that context this paper evaluates the carbon balance of potential land conversion to Jatropha cultivation, biofuel production and use in arid and semi-arid areas. This evaluation includes the calculation of carbon debt created by these land conversions and calculation of the minimum Jatropha yield necessary to repay the respective carbon debts within 15 or 30 years.The carbon debts caused by conversion of arid and semi-arid lands to Jatropha vary largely as a function of the biomass carbon stocks of the land use types in these regions. Based on global ecosystem carbon mapping, cultivated lands and marginal areas (sparse shrubs, herbaceous and bare areas) show to have similar biomass carbon stocks (on average 4–8 t C ha−1) and together cover a total of 1.79 billion ha. Conversion of these lands might not cause a carbon debt, but still might have a negative impact on other sustainability dimensions (e.g. biodiversity or socio-economics). Jatropha establishment in shrubland (0.75 billion ha) would cause a carbon debt of 24–28 t C ha−1 on average (repayable within 30 year with yield of 3.5–3.9 t seed ha−1 yr−1). Land use change in the 1.15 billion ha of forested area under arid and semi-arid climates could cause a carbon debt between 70 and 118 t C ha−1. This debt requires 8.6–13.9 t seed production ha−1 yr−1 for repayment within 30 years. If repayment is required within 15 years, the necessary minimum yields almost double. Considering that 5 t seed ha−1 yr−1 is the current maximum Jatropha yield, conversion of forests cannot be repaid within one human generation. Repayment of carbon debt from shrubland conversions in 30 years is challenging, but feasible. Repayment in 15 year is currently not attainable.Based on this analysis the paper discusses the carbon mitigation potential of biofuels in arid and semi-arid environments. |
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