Some debt swaps are bond-based (a central bank pays interest on a bond created, usually for an NGO, over a period typically of five to seven years); others are government policy programmes (under which the recipient government pledges to implement a policy or initiatives aimed at improving the environment or conservation). Carbon sequestration deals are sometimes linked to debt-for-nature swaps. Through these a developed country or company establishes tree plantations to lock up carbon dioxide to compensate for emissions elsewhere. The developing country land is usually cheap, is not settled by people with legal tenure, and has better tree-growing conditions than colder climates.