## 4 Discussion
### Trade-Offs and Synergies in ESs  
Trade-offs and synergies in ESs show significant differences across service types [43]. Many studies have demonstrated common trade-off relationships between FP and other ESs [44]. As a provisioning service, FP contributes to agricultural productivity. However, agricultural ecosystems often conflict with biodiversity conservation, as they are less suitable for various plant and animal species. Moreover, agricultural ecosystems are less effective for carbon storage compared to forests and grasslands [45]. Similarly, in our study, analysis of the overall temporal changes over the past 23 years indicated that FP and CS exhibit significant trade-off relationships with SC and HQ. This reflects the long-term impact of FP on ecological quality and the adverse consequences of vegetation degradation (Figure 4d). Nevertheless, within the long-term sequence, only the pairs WY-SC and FP-CS exhibited significant synergies, a phenomenon closely related to the improvement in the quality of arable and forest land. Based on our analysis of spatial distribution, strong trade-off relationships in ES correlated pairs (FP-CS, FP-HQ, FP-SC, FP-WY, CS-WY, HQ-WY, and SC-WY) were particularly evident in the high-altitude regions, such as the western Yunnan-Guizhou Plateau and the Nanjing Mountains. The complex geographical and climatic conditions and diverse land use patterns in these regions lead to complex interactions among the ESs, which are profoundly influenced by socioeconomic factors. The combined effects of these factors make it increasingly challenging to achieve balance among FP, WY, HQ, and other ESs in these regions [46]. The trade-off relationships between FP with CS and HQ were widely distributed across the study area. Notably, strong trade-offs were primarily concentrated in Honghe County of Yunnan and the central plains of Guangxi, which serve as major agricultural production regions, where the capacity for other ESs is relatively low [47]. By contrast, the pairs of ESs related to CS and HQ (CS-HQ, CS-WY, and HQ-WY) exhibited significant synergies. Specifically, the synergy between CS and HQ was evident throughout the entire region, while strong synergies between CS and WY and between HQ and WY were primarily concentrated in the central and eastern regions. This phenomenon is closely related to the over 75% forest coverage in the study area, where vegetation cover typically exerts a positive impact on the ecological environment. Trade-offs and synergies among ESs exhibit certain similarities, particularly in terms of the intensity of local service provision and spatial distribution, where both often display comparable patterns [48]. In our study, a strong trade-off relationship appeared between HQ and CS, and strong synergistic relationships between CS and FP and between HQ and FP were consistent at different scales. This suggests that, in terms of spatial distribution, various ecosystem services are closely interconnected between adjacent pixels, and spatial aggregation patterns influence the overall service landscape at larger regional scales. Regarding the overall characteristics, significant shifts in the trade-offs and synergies among the ecosystem services were observed. These shifts reflect the dynamic changes in the competitive and complementary relationships among different services. Such changes may indicate adjustments in the relative demands of these services in response to alterations in land use or ecological conditions. This finding is consistent with the work of several scholars [44; 49]. Therefore, this analysis provides crucial scientific evidence for understanding ecosystem services in the context of sustainable management and contributes to the further optimization of service provision. Based on the results of the trade-off and synergy analysis, we found that although trade-off relationships are generally present, the synergy between certain services can be enhanced by improving land quality.