5 CONCLUSIONS

Integrating complex network analysis and graph theory, we abstracted the ESN into the topological networks of the UAHB in 1995 and 2015, and further assessed these networks’ spatial and temporal evolutions through the constructed index system in terms of network nodes, edges, connectivity, stability, and robustness. We also proposed the corresponding strategies to optimize the structure of the ESN in five aspects. The main findings were as follows:
  1. From 1995 to 2015, the area and quantity of ecological sources increased, and the connection between sources had enhanced. The sources of nature reserves and reservoirs of the western areas increased and made an important contribution to the expansion of ecological security space. The improvement was influenced by government policies. The results also mean that there were more channels for material and energy exchanges between the nodes in the UAHB. However, the development of the ESNs was unbalanced within the UAHB. For example, the nodes with the high comprehensive importance levels were mainly distributed in the southwestern and southern areas.
  2. Assessment of the network connectivity shows that the connectivity in 2015 had significantly improved compared with 1995, but there were isolated nodes in the network with the high network connection complexity. Furthermore, the regional network needed to be given priority to the construction of ecological corridors with higher importance levels.
  3. The robustness assessment shows that the changes of connectivity robustness and vulnerability robustness under human disturbance were more dramatic than those under non-human disturbance. The stability of the ESN was more sensitive to human disturbance, and the nodes with the high comprehensive importance were the key to ensuring the efficiency of network connectivity and information transmission and played an important role in maintaining the stability of the ESN. The results also indicate that the number of nodes had a large impact on the stability of the network. The ESN in 2015 was more connected and more efficient than it was in 1995.
  4. There is room for improvement for the UAHB’s ESN. For example, the areas of the ecological sources in some cities were too small to realize their intended ecological functions. The protection of important ecological sources and the effectiveness of the connection between patches should be strengthened. Ecological breaking points and steppingstones should be given priority to planning and constructing to improve the quality and effectiveness of network connections.
  5. The empirical study shows that a sound assessment framework is an effective tool to enhance the links among the assessment of networks’ structure and function, temporal and spatial evolution, driving factors, and optimization strategies of the ESN. The results of our study will provide theoretical reference and empirical support for other areas facing similar ecological challenges.