Advances in knowledge of processes in soil–tree–crop interactions in parkland systems in the West African Sahel: A review

•Parklands form the most widespread farming systems in the Sahelian zone of West Africa.•Interactions between tree and crop constitute the key element determining their management.•Experiments and modeling has been deployed to understand soil–tree–crop interactions.•Some methodological challenges remain in determining the “park effect” and tradeoffs.