Palynological assemblages from the excavated sediments of Gongsanseong Fortress: Implications for human–environment interactions

• Pollen records show cool-temperate climate with seasonal cold episodes (DACP) • NPPs indicate slope erosion and wet lowland drainage within the fortress. • Palynological, archaeological, and historical evidence suggest outside agriculture. In this study, we investigated the paleoenvironment of the Gongsanseong Fortress during the Woongjin and early Sabi periods (ca. 475–600 CE) in the Baekje Kingdom using palynological and non-pollen palynomorph (NPP) data from 21 excavated soil samples. Pollen assemblages indicated a cool temperate climate characterized by a mixed forest composed of coniferous and deciduous broad-leaved trees. The presence of boreal (subalpine) elements such as Abies, Picea , and Pinus subgen. Haploxylon suggested localized or seasonal cold episodes, reflecting climate instability consistent with the broader Dark Age Cold Period (DACP; ca. 400–765 CE). Agricultural indicator taxa, including Fagopyrum (buckwheat), Perilla , Cucurbita (pumpkin), and Oryza (rice), were primarily recovered from the palace-related administrative complex. However, archaeological and environmental evidence suggested that these crops were not cultivated within the fortress, but were transported from surrounding farmlands for storage or ritual use. The thick rice straw layers (∼100 cm) and the associated fungal spores within the wooden storage features supported this interpretation. The NPP assemblages, including Glomus , freshwater algae, and aquatic invertebrate remains, revealed signs of soil erosion, stagnant water conditions, and active water management. These findings highlight the role of the fortress as a strategic administrative and hydrological hub during climatically unstable periods. Overall, this study demonstrates how environmental stress associated with the DACP may have influenced land use, food management, and social organization within the late Baekje society.