How shallow solum shapes plant selection, tree diversity, carbon stocks and earthworms in coffee agroforestry

Coffee-based agroforestry systems offer a promising approach, contributing to biodiversity conservation, carbon sequestration, and climate resilience. However, limited research exists on how marginal environments, such as shallow soil depths, influence the socio-ecological performance of these systems. Understanding these interactions is crucial for developing effective and adaptive management strategies. This study evaluates how shallow soils in simple and complex coffee-based agroforestry systems influence farmers’ plant selection compared to deep solum area, particularly regarding their tree diversity, soil carbon stocks, and earthworm abundance. Our findings revealed that in shallow soils, farmers prioritize species with shallow root distribution, while in deep solum, farmers tended to select a greater variety of medium to high wood-density perennial trees. A positive relationship between carbon stocks and tree diversity was more pronounced in deep solum and mature plants only. No significant effect of land-use patterns was observed on earthworm biomass and population density across shallow and deep solum. However, the presence of invasive epigeic species (Amynthas spp.) was noted in shallow solum but absent in deep soils. Earthworm activity in shallow solum was significantly influenced by aboveground vegetation, including litter, canopy cover, and tree diversity. To effectively manage shallow solum in coffee-agroforestry systems, maintaining organic matter inputs through diversified tree planting may ensure a continuous supply of organic matter and create a favorable environment for earthworms, thereby supporting sustainable coffee agroforestry and enhancing long-term productivity, biological activity, and soil quality.