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The world's forest cover shrunk by 3.1 per cent between 2000 and 2005, according to satellite observations detailed in a new study.

Hardest-hit were boreal forests - the world's far northern sub-arctic forests - which account for about one-third of this loss, said the report, published in the April 26-30 issue of the Annals of the National Academy of Sciences.

There are several causes of forest destruction, including human cutting and natural phenomena such as fires ignited by lightning, the report said.

The total forest loss was estimated to be 1,011,000sq km, the researchers said.