BEIJING, China (Reuters) -- Humans are stripping nature at an unprecedented rate and will need two planets' worth of natural resources every year by 2050 on current trends, the WWF conservation group said on Tuesday.

Populations of many species, from fish to mammals, had fallen by about a third from 1970 to 2003 largely because of human threats such as pollution, clearing of forests and overfishing, the group also said in a two-yearly report.