Other winners include lawyer Annie Jajir, who is fighting illegal logging in Papua New Guinea, and Brazilian Tarcisio Feitosa, who inspired creation of the world’s largest protected tropical forest area in the Amazon.

Working for group Save My Future Foundation, Mr Siakor revealed that former Liberian president Charles Taylor was selling off the country’s forests to timber companies in order to buy arms.

His work raised the profile of conflict timber internationally and led to UN sanctions on the Liberian timber trade.

Mr Siakor, now director of the Sustainable Development Institute, is also calling on the UN to keep the timber embargo in place so Liberia can document the current state of timber, forest loss and species health in areas of high biodiversity.

The winners, who share a US$750,000 prize, were presented with their awards in San Francisco on April 24.