[Spatiotemporal Variation and Trade-off Synergistic Relationship of Ecosystem Services in Gannan Prefecture]

The Gannan Tibetan Autonomous Prefecture, situated in the upper reaches of the Yellow River Basin, serves as a crucial ecological function area and an environmental fragile zone. Therefore, studying the changes in ecosystem services and their associated trade-offs in this region is important for sustainable development. This study focuses on the Gannan Prefecture, utilizing the InVEST model to analyze the spatio-temporal shifts in land use types from 1990 to 2020. The research evaluates four key ecosystem services within this region： soil conservation, water yield, habitat quality, and carbon storage. Furthermore, it explores the trade-off synergies among these services. The results showed that： ① Between 1990 and 2020, the Gannan Prefecture experienced significant shifts in land use patterns. Construction land, low-coverage grassland, water bodies, and arable land exhibited an increase, while forest land, medium-coverage grassland, high-coverage grassland, and unused land showed a decline. These transformations were widespread across the counties and districts of the Gannan Prefecture, with notable concentrations observed in its northern regions, such as Xiahe, Hezuo, and Zhuoni, and southern areas, including Maqu and Zhouqu. Specifically, arable land underwent predominant conversion into high-coverage grassland, while forest land similarly transitioned into high-coverage grassland. Conversely, high-coverage grassland was converted into forest land, and medium-coverage grassland transitioned into low-coverage grassland. ② Over the past three decades, substantial advancements have been observed in soil conservation and water yield, with increases of 2.90×10⁸ t and 72.17×10⁸ m³. However, changes in habitat quality and carbon storage have been minimal. Spatially, the high values of these four ecosystem services were primarily located in vegetated areas such as forests and grasslands, with counties like Diebu, Zhouqu, Maqu, and Zhuoni serving as primary examples. Between 1990 and 2000, soil conservation and water yield declined in most regions, with the exception of the Maqu County. However, post-2000, a significant increase was noted in soil conservation and water yield in counties and districts such as Xiahe, Luqu, Maqu, and Lintan. Carbon storage remained relatively consistent in counties like Maqu, Diebu, and Zhouqu, with the primary reductions observed in the Xiahe County and Hezuo City. Between 1990 and 2020, habitat quality was found to be deficient in the majority of areas, particularly in counties and districts such as Xiahe, Hezuo, Luqu, and Diebu. Furthermore, progressive expansion of regions experiencing a decline in habitat quality has been observed over time. ③ At spatial scales of 1, 5, and 10 km, a synergistic relationship existed among the four ecosystem services, with soil conservation and carbon storage showing robust synergy. Spatial trade-offs were predominantly observed in regions such as Maqu and Diebu, but as the scale expanded, soil conservation, water yield, carbon storage, and habitat quality tended to become spatially synergistic. These findings provide a scientific basis for ecological sustainable development and land planning in Gannan Prefecture.