Christiansen, Sofus. 1995. “H. Breman & J.-J. Kessler: Woody Plants in Agro-Ecosystems of Semi-Arid Regions, - With Emphasis on the Sahelian Countries. - (Advances Series in Agricultural Sciences 23)”. Geografisk Tidsskrift 95 (januar). https://tidsskrift.dk/geografisktidsskrift/article/view/42057.