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:
- 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.
- 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.
- 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.
- 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.
- 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.