Survival and growth of Acacia senegal (L.) Wild. (Senegalia senegal (L.) Britton) provenances depend on the rainfall at the site of origin

Abstract

• Key message: Variation among provenances of Acacia senegal (Senegalia senegal (L.) Britton) in their survival and growth in height and diameter at two sites in Senegal could be partly explained by the climate at their site of origin and also revealed genotype-by-environment interactions. Breeding programs and forest restoration projects should carefully select germplasm for optimal performance of this socioeconomically important tree species. • Context: Several studies have shown important differences in adaptive properties among provenances (origins) of African savanna tree species, but there is a lack of studies on how these differences are expressed in different environments and age and to what extent they reflect local adaptation. • Aims: This study investigates the survival and growth of trees from 15 African Acacia senegal (Senegalia senegal (L.) Britton) provenances tested in two environments and relates the differences among provenances to the climate at their site of origin and tree age. • Methods: The study is based on 14 years growth in a common garden trial at two sites (Bambey and Dahra, Senegal) that differ in water availability, followed up by later assessment after 23 years at one of the sites. • Results: The variation among provenances in survival, height, and diameter was significant, and differences could be partly explained by the climate at their site of origin. In general, provenances from dry sites survived better at both sites. However, we observed genotype-by-environmental interactions where provenances from dry sites on average performed relatively poorer in height and diameter at the wettest site (Bambey) compared to the drier site (Dahra), while the opposite was the case for provenances from wetter sites. • Conclusion: The results support that divergent selection creates and maintains local adaptation of Acacia senegal provenances in relation to growth (height and diameter) and survival in areas with different water availability. This has important implications for choice of appropriate planting material for tree planting and for conservation of genetic variation among natural populations, but also for prediction of the effects of climate change.