RATIONALE - Local governments in southern Yunnan Province, China, started distributing free shade tree seedlings to coffee farmers in 2012. This prompted a large-scale conversion from intensive monoculture coffee systems towards coffee-agroforestry systems. In this study, we investigated the impacts of some commonly used shade tree species on microclimate and coffee yield and quality shortly after their introduction in coffee fields. METHODS - We selected 3 commonly found shade tree species: Jacaranda mimosifolia (deciduous, light-moderate shade), Bischofia javanica (deciduous, moderate shade), and Cinnamomum camphora (evergreen, dense shade). We marked 90 coffee trees below (treatment) and around (control) the shade tree canopies, and recorded their fruit development throughout a whole coffee cycle, from flowering to harvest, all the way to cup quality testing. In parallel, we recorded the impact of shade trees on microclimate using temperature loggers. RESULTS - The maximum potential coffee yield, indicated by flower set at the start of the growing season, decreased with shade intensity. However, fruit losses during the bean filling and maturation stages were higher in open conditions than under shade. Furthermore, shade trees buffered extreme temperatures and protected coffee trees from frost damages in December 2017 (+0.5 - 1°C). Overall, coffee yield and quality under shade trees with moderate shade intensity (J. mimosifolia and B. Javanica, LAI<3) were similar to that of coffee trees in open conditions. Only C. camphora (dense shade, LAI=6) negatively impacted coffee yield. CONCLUSIONS & PERSPECTIVES - If carefully selected and managed to enhance complementarity with coffee, young shade trees can rapidly provide benefits similar to those expected from older trees, here only 4 years within the transition towards agroforestry. In the case of southern Yunnan Province, the positive tradeoffs from young shade trees (positive externalities related to microclimate an