ameroon's rich tropical forests are about to get some much-needed protection, thanks to a historic deal with France that reduces Cameroon's debt burden at the same time. Under the agreement, Cameroon will invest at least $25 million of its debt to France - instead of having to pay it back - to protect its part of the Congo basin, home to rare forest elephants and hundreds of bird species, as well as local inhabitants like the Ba'Aka people.

Such 'debt-for-nature' swaps were first thought up by Thomas Lovejoy, an American biologist and conservationist. He recognized that the world's richest wildlife areas are usually in developing nations, which both carry the greatest debt and have difficulty paying for environmental protection. The scheme redeems international debt, as long as the money is used to fund environmental protection in the indebted country. It is often a conservation organization that purchases the debt at a discount (yes, you can buy others' debts!) and redeems it in local currency, using the money for conservation on the spot. Sometimes an agreement is made directly between governments - as in the case of the France-Cameroon swap - but this is usually monitored by a conservation body, which can help identify what needs to be conserved and how. Either way, the developing nation saves valuable foreign currency, while managing its natural resources sustainably for both its own - and the planet's - benefit.

The scheme started in 1987, when Conservation International purchased $650,000 worth of Bolivian debt owed to a commercial creditor for just $100,000 - and used the funds to manage the Beni Biosphere Reserve and create more protected areas. By 1996, 16 countries had such swaps, including Costa Rica, Ecuador, Guatemala, the Philippines and Zambia.

In 1998, the United States of America passed a bill authorizing debt-for-nature swaps to protect tropical forests. This led to many more agreements. In 2002, for example, the United States redeemed $6.6 million of Peru's debt in this way with contributions from The Nature Conservancy, Conservation International and WWF. This swap helped protect 10 of the Peruvian Amazon's most biologically rich, critically endangered rainforests, over an area of 110,000 square kilometres.

Of course debt-for-nature can't erase all developing nations' debts. But it does help countries invest in managing the natural resources that they might otherwise destroy to raise money for repayments. And it's hard to argue with Lovejoy, the still-enthusiastic father of the idea, when he reports that debt-for-nature swaps are the world's biggest way of funding conservation.