Advancing the Sustainability of Poplar-Based Agroforestry: Key Knowledge Gaps and Future Pathways

Poplars ( Populus L.) are fast-growing, widely distributed trees with high ecological, economic, and climate-mitigation value, making them central to diverse agroforestry systems worldwide. This study presents a comprehensive bibliometric and content-based review of global poplar-based agroforestry research, using Scopus and Web of Science databases and a PRISMA-guided screening process to identify 496 peer-reviewed publications, covering publications from 1987 to 2024. Results show a steady rise in scientific output, with a notable acceleration after 2013, dominated by agriculture, forestry, and environmental sciences, with strong international contributions and research themes focused on productivity, carbon sequestration, biodiversity, and economic viability. A wide range of Populus species and hybrids is employed globally, supporting functions from crop production and soil enhancement to climate mitigation and ecological restoration. Poplar-based systems offer substantial benefits for soil health, biodiversity, and carbon storage, but also involve trade-offs related to tree–crop interactions, such as competition for light reducing understory crop yields in high-density arrangements, management intensity, and regional conditions. Poplars provide a wide array of provisioning, regulating, and supporting ecosystem services, from supplying food, fodder, timber, and biomass to moderating microclimates, protecting soil and water resources, and restoring habitats, while supporting a broad diversity of agricultural and horticultural crops. However, several critical gaps—including a geographic research imbalance, socio-economic and adoption barriers, limited understanding of tree–crop interactions, and insufficient long-term monitoring—continue to constrain widespread adoption and limit the full realization of the potential of poplar-based agroforestry systems.