Many tropical tree species are difficult to establish in plantations because when planted in pure stands or in open environments, they usually become chlorotic and decline, or they are affected by pests and diseases (Keogh 1996). Another common explanation for this problem is a failure to recognise the important ecological characteristics of these species. The potential for pest problems may increase going from diverse communities (primary forest) through secondary and regenerating forests to enrichment plantings and monoculture plantations (Cobbinah 1997).
Operational scale native monoculture plantations of such valuable hardwoods as Iroko, the African mahoganies and Afromosia have been unsuccessful due to the activities of insects that are largely unrecognised in the natural forests. The problem with Iroko is the gall Phytolama lata that affects the leaves of seedlings. However, the selection of Iroko genotypes that are less susceptible to this pest and its establishment in mixed plantations, has shown considerable promise in humid regions (Cobbinah 1997).
Irrigated Khaya species at Aswan in upper Egypt have also grown without problems such as shoot borer attack. Experience in West Africa indicates that the principal constraint to plantations of the Meliaceae family has been their susceptibility to the shoot borer Hypsipyla robusta.
Most of the successful tropical hardwood plantation schemes in West Africa, for example, are employing utility or standard grade hardwoods such as Terminalia ivorensis, T. superba and Triplochiton scleroxylon (DFID 1998).
Valuable hardwood species that are amenable to vegetative propagation include: Chlophora excelsa, Cordia alliodora, Dalbergia sissoo, Nauclea diderichii, Paraserianthes falcataria, Pterocarpus spp., and Tectona grandis (Perlack et al. 1999).
