The gatekeeper series of the Natural Resources Group at IIED is produced by the Sustainable Agriculture, Biodiversity and Livelihoods Programme. The series aims to highlight key topics in the field of sustainable natural resource management. Each paper reviews a selected issue of contemporary importance and draws preliminary conclusions for development that are particularly relevant for policymakers, researchers and planners. References are provided to important sources and background material. The series is published three times a year and is supported by the Swedish International Development Cooperation Agency (Sida) and the Swiss Agency for Development and Cooperation (SDC). The views expressed in this paper are those of the author(s), and do not necessarily represent those of the International Institute for Environment and Development (IIED), the Swedish International Development Cooperation Agency (Sida), the Swiss Agency for Development and Cooperation (SDC) or any of their partners.