Exploring trade-offs/synergies of ecosystem services and their drivers in Qinghai-Tibet Plateau based on ecosystem service bundles

Understanding the relationships among ecosystem services (ESs) and clarifying their driving mechanism are essential to achieve sustainable ecosystem management and promote human welfare, especially in ecological fragile alpine areas. However, few studies have a clear understanding of the complex relationships among ESs on environmentally fragile regions, and the thresholds of driving factors affecting ESs relationships are still unclear. Taking Qinghai-Tibet Plateau (QTP) as a case, this paper quantitatively evaluated six ESs on QTP including water yield (WY), soil conservation (SC), carbon sequestration (CS), habitat quality (HQ), crop production (CP), and livestock supply (LS) based on multi-source data, applied a self-organizing map to identify the ES bundles, and detected ESs trade-offs and synergies in each ES bundle using partial correlation analysis. Then, the constraint line was utilized to determine the non-linear thresholds of main socio-ecological factors affecting trade-off and synergy. The results showed that the six ESs presented significant spatial heterogeneity. WY, SC and CS exhibited a downward trend from southeast to northwest, the high value area of HQ was in the west regions, while the high CP and LS values occurred mainly in the eastern regions. According to the characteristics of ES bundles, the QTP was divided into multifunctional zone (MZ), LS-HQ synergy zone (LHSZ), crop production zone (CPZ), biodiversity protected zone (BPZ), and ecologically high-risk zone (EHRZ), accounting for 2.51%, 22.40%, 0.82%, 40.54%, and 33.73% of the QTP, respectively. SC had trade-off relationships with WY and CS in MZ, but showed synergies in LHSZ, BPZ, and EHRZ. The relationship between WY and HQ presented synergies in MA and CPZ but presented trade-offs in LHSZ, BPZ, and EHRZ. Among the socio-ecological factors, elevation, temperature, precipitation, and NDVI exhibited significant non-linear influences on trade-offs and synergies with obvious thresholds (R² > 0.5). Overall, elevation had U-shaped constraint effects on ESs trade-offs/synergies, temperature and NDVI showed U-shape and hump-shaped impacts, while precipitation exhibited hump-shaped non-linear effects. The results could provide support for spatial planning and management measures at each ecological zone on the QTP.