Spatio-Temporal Evolution and Driving Factors of Carbon Storage in Hilly Areas in Central Sichuan Based on Land Use Change in the Past 40 Years

This study aimed to clarify the coupling mechanism between land use change and carbon storage in Suining City, Sichuan Province, is a typical hilly region in the upper reaches of the Yangtze River. Besides, the synergistic pathways for "cropland protection–ecological conservation–carbon sequestration" from 1986 to 2035 were explored. This study could provide a theoretical basis for scientifically and rationally promoting the increase of carbon storage and maintaining the sustainable development of agriculture.

Based on land use data interpreted from remote sensing imagery from 1986 to 2023, the InVEST model was employed to estimate carbon storage across multiple time periods. Geographic detectors and ridge regression were used to analyze spatial differentiation drivers. The PLUS model was used to simulate land use and carbon storage changes under four 2035 scenarios: Natural Development (NDS), Urban Development (UDS), Ecological Priority (EPS), and Cropland Protection (CPS). The changing trends and influencing factors of carbon storage in Suining City over the past 40 years were explored.

(1) Land use transformation patterns. Over the past 40 years, the area of cropland, forest land, and construction land has changed significantly, and land use has undergone a three-stage transition: "cropland contraction–urban expansion–ecological restoration". The proportion of crop land decreased from 66.6% to 46.1%, whereas construction land increased from 6.0% to 13.4%. The dominant transition pathway was cropland-to-forest (56.3%). (2) Bidirectional effects on carbon storage. Regional net carbon storage increased by 28.73×10⁵ t, of which the conversion of cropland to forest land was the most important factor driving the increase of carbon storage, contributing 113.16×10⁵ t to the increase of the core carbon increment, followed by the conversion of cropland to shrub land, which increased carbon storage by 13.13×10⁵ t. In contrast, built-up land expansion resulted in a carbon loss of 14.90×10⁵ t. The carbon storage structure was dominated by soil organic carbon, which accounted for more than 84.0%. (3) Driving mechanisms. Topography–vegetation synergistic effects primarily shaped the spatial heterogeneity of carbon storage. Vegetation indices-including Soil Adjusted Vegetation Index (SAVI), Normalized Difference Vegetation Index (NDVI), and Leaf Area Index (LAI)-accounted for over 62.0% of the explanatory power. Due to limited topographic variability in hilly areas (slope coefficient of variation CV≤0.38), topographic factors exhibited a paradox of "high q-value–low contribution" (actual contribution rate <7.0%). (4) Scenario simulations. The EPS scenario was identified as the optimal carbon-maximum pathway, with a marginal increase in carbon storage (0.2%) achieved by strictly controlling construction land (increase limited to 2.2%) and enhancing coordinated restoration of forest and grassland ecosystems (grassland area increased by 69.9%). In contrast, the CPS scenario induced ecological risks: although cropland expanded by 11.6%, carbon storage declined by 0.1%, and wetland conversion exceeded 50.0%.

Based on an analysis of the impact of land use changes over the past 40 years on carbon storage and its driving factors, optimizing land use structure and implementing a “zonal management” policy represented the key pathway to promoting the steady increase of carbon storage in the hilly region of central Sichuan.