Correlations and clines in tree growth and wood density of Balanites aegyptiaca (L.) Delile provenances in Niger

Balanites aegyptiaca (L.) Delile provides wood and other essential products for farming and pastoralist communities in the West African Sahel. In this region, mean annual rainfall decreases in general from south to north and from west to east, so one might expect clinal variation in fitness-related traits in relation to the rainfall gradients. This paper presents results from a provenance/progeny test of 11 provenances sampled in Niger and established at one relatively dry site in Niger. The objectives were to evaluate phenotypic correlations (Pearson r) between tree growth (height, stem diameter) and basic density of the wood, and clines in growth and density at 13 years. Tree growth and wood density were positively correlated, and the correlations differed among provenances. Mean tree height and stem diameter of provenances increased, in general, from the more humid to the drier parts of the sample region. Results suggest that selection of faster-growing trees could lead to an increase in wood volume and density in the subsequent generation, especially in certain provenances; that provenances from drier areas are better adapted to drought; and that tree improvement and conservation programs should collect seeds from populations in the drier areas for planting and conservation.