Coupled regulatory mechanisms and synergy/trade-off strategies of human activity and climate change on ecosystem service value in the loess hilly fragile region of northern Shaanxi, China

Geographic and temporal patterns of ecosystem service value (ESV) and their dynamic coupling response to human activity and climate change are critical for allocating land resources and maintaining healthy ecosystems in the loess hills. Based on five phases of land use data and climate data in Yan'an from 2000 to 2020, our study utilized the value-equivalent method and statistical analysis to systematically reveal the spatio-temporal dynamics of human activity and climate change, as well as their coupled driving mechanisms on ESV, and to establish and optimize synergy/trade-off strategies between them. The findings revealed that land use degree diminished between 2000 and 2020, population distribution increasingly widened. The precipitation fluctuated and increased, but the dryness trend persisted. Significant contributions were made by regulating services, supporting services, grassland, and forest to the interannual total ESV, which grew steadily at a rate of 6.89 % and reached 722.59 trillion in 2020. The total geographical distribution pattern of ESV was unstable, with a medium level of aggregation (0.02–0.06 trillion) in the northern districts and counties and a high level of aggregation (0.06–0.08 trillion) in the southwest and southeast on the grid scale of 1 km × 1 km. ESV had a highly significant synergistic relationship with annual precipitation (AP), but it showed pronounced trade-offs with population density (PD), comprehensive index of land use degree (LUI) and annual mean surface temperature (AMT). Simultaneously, there were profound synergies between the value of regulating, supporting, and cultural services. ESV was primarily positively governed by AP extremely negatively regulated by the synergistic effect of LUI and PD, the optimal regulatory thresholds of LUI, PD and AP for ESV levels of ≥0.06 trillion on the grid scale of 1 km × 1 km were 260, 30,000–50,000 people km−2, and 400–520 mm, respectively. Essentially, controlling the land use degree, expanding farmland and water areas, and stimulating climate humidification were crucial synergistic/trade-off strategies for further balancing and enhancing the value of various ecosystem service functions in sustainable ecological restoration of Yan'an.