Nuts about trees? Tree quantity, species richness, and key species in smallholder agroforestry systems and their associations with groundnut (Arachis hypogaea) yields in Senegal

Abstract In the Sahel region, agroforestry potentially increases crop yields, alongside restoring and retaining soils. However, little is known about how diverse agroforestry systems perform across adoptedagricultural systems of smallholders in the region. We therefore investigate how varying smallholder agroforestry systems in the Senegalese Groundnut Basin associate with groundnut yields. We distinguish agroforestry systems by (a) tree quantity per hectare, (b) tree species richness and (c) quantities per hectare of the most frequently reported tree species in our data. Using data of 492 groundnut farmers, collected in the Groundnut Basin from December 2022 to January 2023, we estimate log-linearized Cobb–Douglas-production functions through ordinary least squares regression. 53 tree species were reported by 93.8% of smallholders. We identify Faidherbia albida , Cordyla pinnata , Adansonia digitata , Anogeissus leiocarpa , and Ziziphus mauritiana as the most frequently reported species. Our results indicate that groundnut yields initially increase with tree quantity and species richness. However, higher tree densities are associated with lower groundnut yields, possibly reflecting increased competition between trees and crops for space, light, water, or soil nutrients. Faidherbia albida trees seem associated with higher groundnut yields only when present in greater numbers. For the species Cordyla pinnata and Anogeissus leiocarpa , additional trees initially associate with increases in groundnut yields. The tree species Ziziphus mauritiana and Adansonia digitata show no clear association with groundnut yields, which may be partly due to their relatively low abundance in the sample. Our results suggest a remaining potential for increasing tree cover and tree species richness, as well as introducing or expanding certain tree species in established agroforestry systems to support groundnut production. Graphical abstract