Greenpeace is withdrawing from the main global group for certifying sustainable wood products, saying it is failing to protect natural forests from exploitation.    Greenpeace, a founding member of the Forest Stewardship Council, said the organization "fell short" of its goals of conserving forests and benefiting society.    The FSC mark, a stylized tree, is sought by paper producers and other wood users as an endorsement they can use in the marketplace to promote their products as sustainable and charge a premium.    The council had successes in some regions, the ...