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15 October 2011 Last updated at 20:28 ET By Mark Kinver Environment reporter, BBC News http://www.bbc.co.uk/news/science-environment-15305271

Trees 'boost African crop yields and food security'

http://www.bbc.co.uk/news/world-15391515 Sources: All population data are based on estimates by the UN Population Division and all calculations provided by the UN Population Fund . The remaining data are from other sections of the UN, the Global Footprint Network and the International Telecommunications Union .

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