Culture and tradition are important components of social sustainability. Traditional and local knowledge are part of culture and belief systems and codified in oral forms and in cultural and religious norms. These cultural meanings are embedded in local people's understanding of the environment, the management of natural resources and agricultural practice (Warren et al., 1995; Posey, 1999). Yams are a staple crop of economic and cultural significance for the people in West Africa. For example, yams (Dioscorea spp.) play a vital role in society in the Dagomba ethnic group in north Ghana. About 75% of farmers in the northern region cultivate yam, as part of the African "yam zone" (Cameroon to Côte d'Ivoire) that produces 90% or 33.7 million tonnes of the world's yams each year. During the celebration of the yam festival boiled yams are smeared on the surface of stones to secure the goodwill and patronage of deities. The Dagomba invoke their gods during the communal labor through which they exchange yam germplasm. Seed yam obtained through communal labor enjoys the blessing of the gods and produces high yields according to tradition. For the Dagomba, the yam has transcended agriculture to become part of the society's culture (Kranjac-Berisavljevic and Gandaa, 2004). Failure to recognize this would result in (1) the breakdown of traditional social structure; and (2) the loss of valuable yam germplasm in many cases.

The knowledge of many indigenous communities has provided almost all their basic food, fibre, health and shelter needs as well as some products for cash income.

Typically, traditional and local KST has been developed through observation and experimentation, over many cycles, to achieve efficient and low-risk human welfare outcomes (Warren et al., 1995). A wide range of local institutions are significant in developing, disseminating and protecting this knowledge as it differs greatly from the specialized knowledge used by research and extension institutions working with agricultural science (Warren et al., 1989). The traditional actors harbor distrust for mainstream organizations and are comparatively marginalized by them. Consequently, identifying an appropriate and acceptable means of making use of traditional knowledge and protecting the valuable rights of indigenous communities to their traditional knowledge is a priority if this knowledge is not to be lost, and if the communities are to benefit (ten Kate and Laird, 1999). A good example is the patent protecting the rights of women in Botswana to traditional knowledge associated with Marula kernel oil (www.phytotradeafrica.com/awards/ criteria.htm).

The important role of livestock for poor people's livelihoods has been sustained primarily through the effectiveness of indigenous knowledge.

Livestock are an important asset of many poor people, particularly in sub-Saharan Africa and south Asia (Thornton et al., 2002, 2004), providing a source of food, cash income,

manure and draft power and strengthening their capacity to cope with income shocks (Ashley et al., 1999; Heffernan and Misturelli, 2001). In India, for example, livestock holdings are more equitably distributed than land holdings (Taneja and Birthal, 2003). Livestock ownership directly and indirectly affects the nutritional status of children in developing countries (Tangka et al., 2000). In Africa, the livestock sector, particularly in arid and semiarid areas, depends to a large extent on traditional and local knowledge for animal management and animal breeding (Ayantude et al., 2007, but receives little investment in international and national research. The depth of local knowledge has advantages when developing localized initiatives, for example, in animal feeding and forage production. Productivity in animal agriculture systems can be increased under dry conditions without great external inputs (Lhoste, 2005). Participatory methods for diagnosis of animal diseases have also shown promise, both in characterization of diseases and the linkages between local knowledge and modern veterinary knowledge (Catley et al., 2001). Such participatory local analysis has been used to develop control programs adapted to local conditions and knowledge (Catley et al., 2002).

3.2.3.3.3 Linking scientific and indigenous knowledge and management capability

Significant gains have been made when farmer innovation (particularly in small-scale agriculture) is appropriately linked to formal AKST.

Formal research and extension organizations have often not recognized the contribution of farmers' knowledge and strategies (Richards, 1985; Sibelet, 1995). However, there are good examples in plant breeding where farmers have communicated their local knowledge to researchers, and worked together in experimentation and decision making (Hocdé, 1997), researchers and stakeholders jointly designing experimentation, sharing and validating results (Liu, 1997; Gonzalves et al., 2005; Liu and Crezé, 2006). Agroforestry researchers working with farmers have investigated progressively more complex issues together, integrating biophysical and socioeconomic disciplines to resolve the sustainability problems in areas where poverty and environmental degradation coexist. This has required a unique mixture of new science (Sanchez, 1995) with local understanding of the day-to-day concerns of resource-poor farmers; the approach enhances the adoption of new ideas and technologies (Franzel and Scherr, 2002). Innovations like these evolve as a result of collective learning as well as from the pressure to constantly adapt to the changing economic environment.

The influence of social institutions on land management, based on local knowledge and norms, may be undermined by policies based on the different perspectives of professionals.