Understanding the root traits of tree species is of great importance for selection of trees in dry zone agroforestry systems. We investigated root growth of nine dryland tree species in West Africa and assessed the effect of drought stress on biomass allocation to root systems as function of soil depth. Seedlings were planted in 2m tubes inserted into the soil and subjected to three watering treatments: top irrigation, low irrigation at 50 cm depth, and drought. After 8 and 12 months, we assessed root growth and architecture, and supplemented with assessments of water potential, leaf phenology, and above-ground growth. Results showed large differences in rooting profile of the tree species. Drought induced faster root growth and all species reached the maximum depth after 12 months. Rooting depth was reduced under top irrigation for Adansonia digitata, Sterculia setigera and Anacardium occidentale that concentrated root biomass in the upper soil layers, while Acacia senegal, Acacia nilotica and Faidherbia albida had deeper root systems. Acacia species showed clear differences in leaf water potential between treatments while A. digitata and S. setigera appeared to be water conserving under drought. We discuss results in terms of isohydry/an-isohydry and evergreen vs. deciduous habits.