From past experience, domesticated trees are frequently grown in monocultures, but they could play an important role in species-rich multistrata agroforests (Leakey, 1996b). The development of multistrata systems that include cultivars of domesticated trees could increase the profitability of these agroforests. Thus this approach could, it seems, go a long way toward the establishment of land uses that will fulfill the needs of rural and urban populations for food and income, while maintaining much of the biological diversity of forests or rehabilitating degraded ecosystems.
Much research will be needed, however, to achieve this and to demonstrate that productivity and profitability are not necessarily environmentally damaging. Evidence already emerging from studies to develop viable alternatives to slash-and-burn agriculture suggests that the greenhouse gas emissions, especially methane, from areas where sources such as paddy fields are juxtaposed with perennial vegetation are lower than from areas monocropped with rice (van Noordwijk et al., 1995a). However, the successful establishment of trees on cleared sites is known to suffer from changes in the populations and species diversity of symbiotic microflora associated with land clearance (Leakey et al., 1993; Mason and Wilson, 1994), and similar changes probably occur in the beneficial micro- and mesofauna above- and belowground. Evidence exists for the negative effects of site clearance on soil fauna populations (Eggleton et al., 1995) and for the need to restore them to ensure soil fertility.
A challenge for agroforestry research is to develop economically and socially acceptable land-use systems that function like undisturbed ecosystems and maintain biodiversity. Could complex multistrata agroforests, like those of Sumatra, be developed in humid West Africa and in Latin America? The answer is almost certainly yes. Indeed, simple indigenous multistrata systems already exist, such as the cocoa farm, and the compound gardens of West Africa (Okafor and Fernandes, 1987), while in the Peruvian Amazon, multistrata agroforests have been found to be an economically attractive system (Table 2).
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