Genetic improvement of west African tree species: past and present

Abstract

Internal and external demand for indigenous tropical hardwoods is increasing in many West African countries, while natural forests have become depleted as a result of over-exploitation. Selective logging has probably eroded the gene pools of some tiaditionally well-known species. Owing to a lack of information and various biological problems, insufficient seed is available for the reforestation programmes which are required to reduce the deforestation pressures on the surviving areas of natural forest. The identification of these biological problems, and the realisation of their imminent environmental and commercial consequences, resulted in enhanced research efforts in various West African countries in the late 1960s. Studies on seed management, provenance evaluation, vegetative propagation and genetic selection for improved yield and quality are some of the areas of reseamh initiated for the domestication of a few important indigenous hardwood species. These developments by the individual countries of West and Central Africa have been supported by the UK Overseas Development Administration, the International nopical Timber Organisation, the Danish International Development Agency and the World Bank. Provenance trials and gene banks have been established in Ghana, Cameroon, Nigeria and in COte d'Ivoire, representing much of the geographical range of certain species, with clonal testing also initiated in Nigeria, C6te d'Ivoire, and currently Cameroon. Clonal evaluations have resulted in better understanding of genetic variability, and for 7'riplochiton scleroxylon (obeche) an overall gain in stem volume of over 30% has been achieved. Studies on the early growth of obeche clones have included the relationship between branching frequency and apical dominance, as well as measurements of photosynthesis, as aids to early selection of desirable genotypes. Developments from these research efforts have enhanced reforestation, particularly in Côte d'Ivoire and Nigeria. At least in the short term, substantial benefits could be achieved in West Africa by the establishment of clonal plantations of indigenous trees, exploiting variation present in wild populations. Renewed efforts in this area could help to ensure a continuing timber supply in the future