Ecosystem Carbon Storage in Southwest China’s Ecological Security Barrier Zone: Spatiotemporal Dynamics and Multi-Scenario Analysis

Land use/cover change (LUCC) strongly regulates ecosystem carbon storage and provides a critical entry point for carbon-oriented territorial spatial governance. However, balancing carbon sequestration, food security, urban expansion, and ecological protection remains challenging in Southwest China’s Ecological Security Barrier Zone (ESBZ). In this study, we coupled the Patch-generating Land Use Simulation (PLUS) model with the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) carbon module to reconstruct LUCC and carbon-storage dynamics during 1999–2024 and to project land-use patterns and carbon storage in 2049 under four scenarios: Natural Development (NDS), Urban Development (UDS), Cultivated land Protection (CPS), and Ecological Protection (EPS). Unlike most existing PLUS–InVEST studies focused on cities, watersheds, or single provinces, this study targets a national ecological security barrier and integrates land-use evolution, carbon-storage responses, scenario trade-offs, and zoning-oriented governance into one analytical framework. It therefore provides spatially explicit evidence not only for carbon-oriented land management but also for interprovincial ecological compensation and coordinated ecological security governance in ecologically fragile regions. The 2024 land system was dominated by forest land (56.40%), cultivated land (25.47%), and grassland (16.09%). From 1999 to 2024, forest land expanded by 1.966 × 104 km2, whereas cultivated land and grassland decreased by 9.738 × 103 km2 and 1.874 × 104 km2, respectively; 92.65% of construction-land expansion originated from cultivated land conversion. Correspondingly, total carbon storage followed a “fluctuation–decline–recovery” trajectory, decreasing from 3.833 × 1010 t in 1999 to 3.820 × 1010 t in 2014, before rebounding to 3.831 × 1010 t in 2024. Pronounced provincial heterogeneity was observed: Sichuan and Yunnan jointly contributed about 76% of regional carbon storage, while Chongqing and Guizhou remained relatively low. By 2049, EPS produced the highest carbon storage (3.854 × 1010 t), whereas CPS, UDS, and NDS all led to lower values than in 2024. These contrasts indicate that the four scenarios do not represent a simple ranking of “better” or “worse”, but rather different trade-offs among carbon sinks, cultivated land protection, urban development, and regional equity. Overall, the results support province-differentiated, zoning-based land governance and highlight the need to coordinate ecological protection, cultivated-land conservation, urban growth control, and interprovincial ecological compensation to enhance carbon sequestration and safeguard ecological security in the ESBZ.