Genetic variation and clines in growth and survival of Prosopis africana from Burkina Faso and Niger: comparing results and conclusions from a nursery test and a long-term field test in Niger

Rural communities in West Africa value Prosopis africana for its wood and other essential products and environmental services. The climate is becoming hotter and drier with more variable rainfall, so it is important to identify provenances that are better adapted to a hotter, drier climate. Some tree improvement research programs use nursery tests to identify better adapted provenances, but are conclusions comparable to those from field tests? We analyzed data (height, root dry weight, shoot dry weight, root/shoot ratio, survival) from a provenance/progeny nursery test of P. africana at 8 months, and compared the results with a field test at 11 and 13 years. The tests included 275 families from 28 provenances in the Sahelian and Sudanian ecozones of Burkina Faso and Niger, and were established at one relatively dry site in Niger. The proportion of total variance due to provenances and families within provenances was greatest for root/shoot ratio, and root/shoot ratio had the highest heritability of growth variables in the nursery. Provenances with smaller seedlings and larger root/shoot ratios in the nursery had better growth and survival in the field, and were from drier locations. Mean annual rainfall of provenances was the best predictor of provenance growth and survival in the field, followed by provenance height and root/shoot ratio in the nursery. We recommend that tree improvement research programs in the Sahelian and Sudanian ecozones of West Africa identify P. africana provenances that are from drier locations and have smaller seedlings and larger root/shoot ratios in the nursery for planting in agroforestry projects in rural communities.