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Desertification prevention. Man standing by a plantation (upper right) where plants that have been planted to help stop further desertification of areas around the Sahara Desert. Increasing desertification is an ever-present problem in regions bordering the Sahara. Photographed in Tarfaya, Morocco. (KEYSTONE/SCIENCE PHOTO LIBRARY/THIERRY BERROD, MONA LISA PRODUCTION/ SCIENCE PHOTO LIBRARY)