Scattered tree species’ leaf litter quality and impact on soil properties in enset homegardens of South Ethiopia: a case for conserving old trees

Enset ( Ensete ventricosum ) is among the under-researched African crops that serve as a staple food crop in South Ethiopia. Despite potential benefits, tree species are rarely integrated into enset farms, and their potential to enhance soil fertility in enset systems remains largely unexplored. As a consequence, reliable recommendations for farmers are lacking. This study aimed to evaluate the influence of dominant tree species on soil physicochemical properties in enset-producing homegardens in the Gamo Highlands of South Ethiopia. Under the five most common tree species, we measured 11 soil health indicators and compared them at three radial distances from tree trunks. Those results were compared to the elemental composition of the tree leaves and their decomposability. In on-farm observations, soil physicochemical properties varied widely between farms, yet significant intra-farm differences were observed only in TN, Pav, K, Ca, Mg, and cation exchange capacity. Tree species identity and radial distance had no significant effect on most soil physicochemical properties; however, their interaction significantly influenced TC, C/N ratio, Ca, and CEC, with the highest values observed beneath canopies of larger, older Ficus sur trees. Nevertheless, leaf litter elemental composition differed significantly among tree species. Croton macrostachyus had the lowest C/N ratio and the highest nutrient concentrations, while Cordia africana decomposed at a slower rate. Overall, our field observations suggest that large, old trees can contribute to maintaining soil fertility and therefore should be conserved as much as possible within enset farming systems. The potential of planting new trees to replenish soil nutrients will, thus, depend on the consistency of the measure, the density of trees, and the leaf biomass to be incorporated over time. Furthermore, given the wide variation in litter properties among species, recommendations to farmers should match tree characteristics to specific soil conditions and amendments to best enhance fertility based on their needs.