Varied ecological and socio-economic conditions have given rise to specific forms of agroforestry in different parts of Africa. Policies that institutionally segregate forest from agriculture miss opportunities for synergy at landscape scale.
More explicit inclusion of agroforestry and the integration of agriculture and forestry agendas in global initiatives on climate change adaptation and mitigation can increase their effectiveness. They also identify research gaps and overarching research questions for the contributions in this special issue that may help shape current opinion in environmental sustainability.
Throughout Africa, agroforestry systems come in a wide variety of shapes and forms. Many of these systems have little more in common than the coincidence of woody perennials with agricultural crops and/or livestock. Basic data collection by the FAO does not clearly stress the segregation between forests and agricultural landscapes with trees. This can be seen as an historical anomaly rather than a reflection of incompatibility between annual and perennial plants within a farming system.
Trees or shrubs on farms and in landscapes can occur as solitary individuals, in lines, as woodlots or in the seemingly random constellations that characterized the forest that was present before the establishment of agriculture.
Depending on the environmental, climatic, economic and socio-cultural niches they occupy, different types of agroforestry systems have arisen in different places. Some prominent examples that illustrate the diversity of agroforestry are the parkland systems of the Sahel, multistory homegardens on Mt. Kilimanjaro in Tanzania, cocoa systems in Côte d’Ivoire and rotational woodlots in Kenya. A number of approaches have been proposed for defining a typology of agroforestry practices and systems, but inclusion of multiple characteristics is necessary for grasping all major distinctive attributes of agroforestry systems.
Several agroforestry practices can be relevant for different agro-ecological zones, and many systems with a range of different compositions can fulfill essentially the same functions for livelihoods and landscapes. There is thus no single classification scheme that can be universally applied. What differentiates agroforestry from other land uses is the deliberate inclusion of woody perennials on farms, which usually leads to significant economic and/or ecological interactions between woody and non-woody system components.
In most documented cases of successful agroforestry establishment, tree-based systems are more productive, more sustainable and more attuned to people's cultural or material needs than treeless alternatives. Yet agroforestry is not being adopted everywhere, and better insights are needed into the productive and environmental performance of agroforestry systems, socio-cultural and political prerequisites for their establishment, and the trade-offs farmers face in choosing between land use practices.
These site factors are likely to vary at fine spatial and possibly temporal scales, making the development of robust targeting tools for agroforestry intervention a key priority in agroforestry research.
The framework under which agroforestry could contribute to food security, social wealth and climate change alleviation requires a clear understanding of the components and processes that are relevant for sustainable management of benefit flows from ecosystem services in changing agricultural landscapes.
A Guest Editorial