Quantifying the Indirect Environmental Effects of Land Use Change on the Terrestrial Carbon Cycle in China During 1990–2020

Carbon emissions from land use change (LUC) play a critical role in the global carbon budget and serve as a fundamental basis for national land-use planning. However, existing estimates are typically derived from direct human activities, while the environmental indirect effects driven by both natural and anthropogenic factors are often overlooked. To date, no studies have explicitly differentiated between the direct and environmental indirect effects of interannual LUC. This omission may bias estimates of LUC-induced carbon emissions and undermine the effectiveness of carbon reduction policies. Here, we proposed a novel accounting method that employed a process-based dynamic vegetation model to quantify interannual LUC-induced carbon fluxes (LUCF) in China from 1990 to 2020, further distinguishing them into direct (LUCF-d) and environmental indirect fluxes (LUCF-ind). The results indicate that China's overall LUCF from 1990 to 2020 functioned as a carbon source, with a trend shifting from a source in the 1990s to a sink in the past decade. Over the past 30 years, LUCF-ind sequestered 1.39 ± 1.05 TgC yr⁻¹, offsetting approximately 25% of the emissions from LUCF-d. The South and Central regions are the primary areas for the trade-off between LUCF-d and LUCF-ind, with indirect environmental effects reducing direct emissions by 13.3% and 13.7%, respectively. This study aims to enhance the effectiveness of national-level land use carbon reduction policies by integrating environmental indirect effects and providing methodological references for other countries.