## 1 Introduction  
To tackle climate change and accelerate sustainable development, the Chinese government has set the strategic goals of peaking CO\({}_{2}\) emissions by 2030 and achieving carbon neutrality by 2060 [1]. The carbon sink of terrestrial ecosystems in China (0.24 Pg C\(\cdot\)yr\({}^{-1}\)) has significantly offset some of the carbon emissions from fossil fuel burning and land use change (10-40%) over the past decades [2]. From the perspective of sink enhancement, the Chinese government proposes strengthening ecological protection to consolidate the carbon sink capacity of natural ecosystems [3]. However, there are still great uncertainties in the future carbon sequestration potential of ecosystems. Net ecosystem productivity (NEP) is the difference between gross primary productivity (GPP) and ecosystem respiration (ER) [2]. NEP is commonly used as a measure of carbon sinks in terrestrial ecosystems. If the NEP is positive, the ecosystem is a carbon sink, and if not, it is a carbon source. Regional terrestrial ecosystem carbon balance estimation methods include field inventories [4; 5; 6; 7; 8], terrestrial ecosystem models [9; 10; 11; 12], atmospheric inversion methods [13; 14; 15; 16], and upscaling methods of flux observation data [17; 18; 19; 20; 21], but there are some differences in the estimation results of different methods. In particular, ecosystem modeling has become an effective tool for understanding and evaluating terrestrial carbon cycles at the sample point at both regional and global scales [22; 23; 24; 25; 26; 27]. It can quantitatively distinguish the contributions of different drivers to changes and accurately evaluate the impacts of future climate change on carbon sinks. The forest ecosystem carbon budget model for China (FORCCHN) is a self-developed patch model based on individual growth processes and meteorological data. There are four main characteristics: (1) the cycle and transformation processes of carbon, nitrogen, and water at different interfaces of atmosphere-plant-soil are organically combined; (2) the drivers of forest ecosystem carbon balance are not predetermined by the current climate and ecosystem statistical relationships but rather are based on individual physiological-ecological process mechanisms that are coupled; (3) the carbon flux of the forest is determined by the individual growth of the stand so that the carbon budget can be simulated more scientifically and reasonably; and (4) models can accurately elaborate woody biomass and are more advantageous in predicting the effect of climate factors on carbon fluxes. The model has been used to simulate the carbon balance of different types of forests in China and the world [28; 29; 30; 31] and performs particularly well in capturing the temporal variability and magnitude of carbon fluxes in deciduous broadleaf and evergreen broadleaf forests. Therefore, the model is suitable for assessing the carbon sequestration potential of forest ecosystems. Both ecosystem carbon conservation and sink enhancement are considered to be the greenest, most economical and scale-effective technology pathways [32]. In recent decades, forest ecosystems have contributed more than 80% of the annual average terrestrial carbon sink in China [7; 33; 34]. [PERSON] et al. found that the spatial distribution pattern of carbon sequestration in China's forests was high in the east and south and low in the west and north through ChinaFlux [35; 36; 37; 38]. Moreover, the southwest region is confirmed to be one of the regions with the largest carbon sequestration capacity through various research tools, such as atmospheric inversion, flux observation, and ecological modeling [38; 39; 15; 40]. In addition, the southwest forest region is the largest natural forest area and the implementation area of major forestry ecological projects in China, but there is a lack of research on the future carbon sequestration potential of this region.