Forest resources in Rwanda have steadily decreased over time, especially since the beginning of this century, due to rapid population growth, a limited land base and growing competition for resources. But, in spite of dwindling tree resources, the cultivation and management of woody species remains important in Rwandan farming systems. Trees are the primary sources of energy and construction material. Their cultivation is encouraged to prevent soil erosion, to increase soil fertility through mulching and green manure, and to provide products such as fruit, medicine and fibres. Over time, farmers have generated extensive knowledge about the management of indigenous tree species for these purposes. In addition, they have acquired and adapted knowledge about exotic species and silvicultural practices.