A review of the direct and indirect effects of African agroforestry trees

Abstract

Trees play a crucial role in regulating agroforestry systems by influencing nutrient cycling, supporting biodiversity, and creating a microclimate that benefits annual crops. They facilitate the flow of minerals and organic matter while improving soil moisture and air humidity. However, trees can also exhibit antagonistic effects on crops and other annual plants. Numerous studies across Africa have explored the ecological and physiological functions of agroforestry trees.This review synthesizes existing scientific literature on the effects of these trees, with a focus on growth patterns, carbon sequestration, and interactions with crops. Findings indicate that agroforestry trees exhibit diverse growth rates and carbon storage capacities, both of which are strongly influenced by environmental conditions. Species composition and agroforestry management practices further impact tree performance, particularly in terms of carbon sequestration. Additionally, nutrient content and litter decomposition rates are significantly correlated with climatic factors (P ≤ 0.001). While litter decomposition enhances nutrient availability, the presence of antinutritional compounds can slow this process. Trees also contribute to climate regulation by buffering temperature fluctuations and improving local humidity levels. However, not all interactions are beneficial, certain tree species release tannins and phenolic compounds that inhibit seed germination, reduce crop growth rates, and interfere with leaf pigmentation. This study provides valuable insights into the management of agroforestry trees in African agricultural systems, emphasizing the need for strategic species selection and management practices to maximize benefits while minimizing negative interactions with annual crops.