The challenge of HIV/AIDS: Where does agroforestry fit in? - World ...

14World Agroforestry into the FutureIdentification, capture, retention andprotection of genetic diversityDomestication has been defined as humaninducedchange in the genetics of a speciesto conform to human desires and agroecosystems(Harlan 1975). It is not surprisingtherefore, that much of the work to domesticateagroforestry trees has focused on boththe identification of intraspecific genetic variabilityof the priority species and the vegetativepropagation techniques to capturethese superior combinations. However, onedesirable trait is not necessarily correlatedwith another: thus large fruits are not necessarilysweet fruits, and do not necessarilycontain large nuts or kernels. This multitraitvariation, coupled with the variability ofeach individual trait, results in a considerableopportunity for selection of trees withgood combinations of traits, but also makesit more unlikely that an ideal tree will befound. Thus, large numbers of trees have tobe screened to find the rare combinations oftraits. This rapidly becomes impractical andvery expensive. Consequently, the practicalapproach is to search for trees that have particularmarket-oriented trait combinations(or ideotypes) – such as big, sweet fruits forthe fresh fruit market (a fruit ideotype) orbig, easily extracted kernels for the kernelmarket (kernel ideotype), etc.Trees can also be selected for production traitssuch as yield, seasonality and regularity of production,reproductive biology, and reductionof susceptibility to pests and diseases (Kengueet al. 2002). High yield is obviously a desirabletrait in any cultivar, but, within reason, may notbe as important in the early stages of domesticationas the quality attributes. Fruiting seasontime/length, ripening period and seedlessnessare other important variables that could be selectedfor (Anegbeh et al. 2005).Such great intraspecific genetic diversityneeds to be preserved. Domestication isgenerally considered to reduce geneticdiversity, a situation that may occur wherethe domesticated plant replaces or dominatesthe wild origin, but is probably notthe case at the current level of domesticationof agroforestry trees. For example, therange of fruit sizes in on-farm populationsof Dacryodes edulis and Irvingia gabonensishas been increased by the early stagesof domestication (Leakey et al. 2004).Nevertheless, the maintenance of geneticdiversity is essential. Modern moleculartechniques can identify the ‘hot-spots’ ofintraspecific diversity (Lowe et al. 2000),which should, if possible, be protectedfor in situ genetic conservation, or be thesource of germplasm collections if ex situconservation is required. In addition, whendeveloping cultivars, they should originatefrom unrelated populations with very differentgenetic structures.Having identified the superior trees withthe desired traits, the capture of tree-to-treevariation using techniques of vegetativepropagation is relatively simple and wellunderstood (Leakey 2004b; Leakey et al.1996; Mudge and Brennan 1999). Cuttingsfrom mature trees have a low rate of propagativesuccess, and the number of peoplewith the appropriate skills to carry it outmay be a constraint to its widespread applicationin the future (Simons and Leakey2004). However, propagation by juvenileleafy cuttings is very easy for almost all treespecies and is currently the preferred optionfor participatory domestication in villagenurseries (Mbile et al. 2004; Mialoundamaet al. 2002; Shiembo et al. 1996;Tchoundjeu et al. 2002b).Cultivation and the growth of cultivarsThe final stage of the domestication processis the optimal integration of selected plantsinto the farming system (Leakey and Newton1994a; 1994b). In African farmland, awide range of densities and configurationsare grown (Kindt 2002). In Cameroon, forexample, cocoa agroforests have beenreported to contain around 500 cocoabushes growing with 15 other types of treesand shrubs (Gockowski and Dury 1999).Agroforestry is expected to provide positiveenvironmental benefits on climate changeand biodiversity (Millennium DevelopmentGoal 7). However, research is needed todetermine the impacts of such diversity onagroecosystem function (Gliessman 1998;Leakey 1999b; Mbile et al. 2003); carbonsequestration (Gockowski et al. 2001) andtrace gas fluxes; and on the sustainabilityof production and household livelihoods.MarketsThe term agroforestry tree products (AFTPs)is of very recent origin (Simons and Leakey2004) and refers to timber and non-timberforest products (NTFPs) that are sourcedfrom trees cultivated outside of forests, todistinguish them from NTFPs extractedfrom natural systems. However, someproducts will be marketed as both NTFPsand AFTPs during the period of transitionfrom wild resources to newly domesticatedcrops. Consequently, both terms are usedin the following sections.Economic and social benefits fromtrading AFTPsTo be effective, there must be a link betweentree domestication and productcommercialization, which requires theinvolvement of food, pharmaceutical andother industries in the identification of thecharacteristics that will determine marketacceptability (Leakey 1999a). In West andCentral Africa, a number of indigenousfruits and nuts, mostly gathered from farmtrees, contribute to regional trade (Ndoyeet al. 1997). In Cameroon, the annual tradein products from five key species has been