Annual Report 2009

Prosopis africana and Balanites aegyptiaca are native tree species in the West African Sahel. Rural communi- ties use their durable wood for construction poles, hand- les for farm implements, firewood, charcoal and artisan products. Tree growth and wood density are key traits for these and other timber-tree species: growth determi- nes potential wood volume, and density is an important indicator of wood quality properties. For example, den- ser wood has more lignin, which generally increases its strength, stiffness and calorific value. These in turn make the wood more valuable for construction wood and energy. Correlations between tree growth and wood properties are important in order to assess whether selecting faster-growing trees will have a positive, neu- tral or negative effect on the wood properties. There are strong latitudinal and longitudinal gradients in rainfall in the West African Sahel. Therefore, one would expect genetic differences among natural popu- lations as a result of natural selection along the gra- dients. The first provenance/progeny tests of P. africana and B. aegyptiaca were established in Niger. In the 2008 Annual Report, we reported that larger trees of P. africana tended to have denser wood, and that mean tree growth and wood density of P. africana provenances increased from the more humid to the drier parts of its sample region. In this chapter, we discuss and correla- tions between growth, wood density and calorific value of P. africana and B. aegyptiaca; and clinal variation in tree growth of B. aegyptiaca and wood calorific value of P. africana and B. aegyptiaca.

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