Studying the spatiotemporal variations of the ecological network and carbon utilization efficiency in Southeast Tibet based on complex network theory

• To understand the carbon sequestration capacity of vegetation in Southeast Tibet over the past ten years, laying a scientific foundation for addressing ecological issues, landscape patterns, and developing ecological networks in Southeast Tibet. • The number of ecological nodes and corridors has been decreasing annually. • Ecological construction in the western regions should continue to be strengthened. • Ecological stepping stones should be added, and the length of corridors should be reduced to improve ecosystem CUE. Currently, with the gradual advancement of urbanization and industrialization, ecological patches are severely fragmented and corridors are cut off, leading to the construction of regional ecological networks that can connect fragmented patches and corridors with regional characteristics. However, there is limited research on the relationship between ecological networks and Carbon Utilization Efficiency (CUE) based on complex network theory. This paper takes the ecologically fragile Southeast Tibet as the research area and investigates the variation patterns of CUE through the establishment of ecological spatial networks. The Graphab Model is employed to extract the ecological space network of Southeast Tibet. The Graphab Model integrates the complex network with the ecological space network to compute the topological index of ecological nodes and the overall ecological network. Later, MOD17A2HGF GPP and MOD17A2HGF PSN net data from 2013 to 2021 are used as the primary data for calculating the CUE of ecological nodes. The connection between topological index and ecological nodes is analysed. The results indicate that, with interannual variations, ecological nodes dropped by 15, and the number of ecological galleries decreased by 7. However, the average values of various topological indices showed an increasing trend, suggesting that the ecological remediation items in Southeast Tibet have made some achievements. Nevertheless, the analysis of CUE in Southeast Tibet reveals a downward trend in the carbon fixation rate of vegetation in recent years. Through correlation analysis, it was found that the correlation between various topological indices and CUE was the lowest and insignificant in 2013, while from 2015 to 2021, all topological indices were significantly positively correlated with CUE. Through Principal Component Analysis (PCA), It is recommended to reduce and shorten redundant ecological corridors by aggregating small ecological patches and increasing stepping stone patches, and increase ecological galleries to enhance the carbon fixation ability of plants. This research lays a scientific foundation for addressing ecological issues, landscape patterns, and developing ecological networks in Southeast Tibet.