Abstract: Rice terraces have long provided multiple ecosystem services (ESs), yet quantitative assessments of their trade-offs and synergies using biophysical models remain limited, particularly in heritage agricultural landscapes. However, these landscapes face mounting pressures from climate change, rural depopulation, and inadequate maintenance of terrace infrastructure, threatening both their ecological functions and cultural value—a concern underscored by China’s seven GIAHS-inscribed southern mountain rice terrace systems. This study focused on the Longji Rice Terraces (Longji Township), Longsheng Multi-ethnic Autonomous County, Guangxi, China (232.7 km²; elevation 251-1 906 m), a site designated as both a GIAHS site and a National Wetland Park. Using annual land use and land cover (LULC) data at 10 m resolution derived from Sentinel-2 imagery, we assessed four ES categories for 2017—2022 with corresponding InVEST sub-modules: Habitat Quality (HQ), Sediment Delivery Ratio for Soil Conservation (SC), Annual Water Yield (WY), and Carbon Storage (CS). Spearman correlation coefficients identified trade-off and synergy relationships among services, and Production Possibility Frontier (PPF) curves delineated optimal regulation intervals for service pairs exhibiting trade-offs. Results revealed four key findings. First, regarding temporal trends, CS increased steadily (2.8%), whereas HQ, SC, and WY declined by 1.02%, 28.84%, and 4.18%, respectively. Notably, SC underwent a precipitous 45.47% decline during 2017—2020, closely linked to weakened terrace maintenance resulting from tourism contraction over the same period. Second, regarding spatial patterns, HQ and CS displayed a ‘globally high, locally low’ distribution; WY exhibited lower values in the central area and higher values in surrounding areas; and SC showed an interlocking mosaic of high and low values driven by topographic dissection. Third, synergies predominated among the four services, manifesting as one trade-off pair, four synergy pairs, and one unstable relationship. The CS-WY pair represented the strongest trade-off (mean R=−0.41), while the HQ-CS relationship shifted from a short-term trade-off to a synergy over the study period. Fourth, PPF analysis indicated that normalized WY values remained stable within 0.78-0.92, with CS substantially constrained by WY: when normalized WY approached approximately 0.92 (corresponding to roughly 1 285 mm/a), normalized CS tended toward zero, whereas when normalized WY fell to approximately 0.78 (roughly 1 147 mm/a), CS approached its maximum. This finding suggests that modest reductions in water yield can yield substantial gains in carbon storage. These results provide spatially explicit, quantitative evidence to support stabilization of soil conservation on the Longji terraces, balanced regulation of water resources and carbon sinks, and coordination of habitat protection with moderate tourism development, while also offering decision-support references for regional carbon peaking and carbon neutrality goals. Specifically, we recommend strengthening routine terrace maintenance to stabilize soil conservation capacity, expanding reservoir storage to buffer the spatiotemporal unevenness of water supply while simultaneously mitigating the WY-CS trade-off, coordinating habitat protection with moderate tourism development, and enhancing adaptive capacity to extreme climate events. Future research should integrate multi-source remote sensing with long-term field observations to improve model accuracy and extend the temporal scope of ecosystem service assessments in heritage terrace landscapes.