Construction and evaluation of ecological networks among natural protected areas based on “quality-structure–function”: A case study of the Qinghai-Tibet area

The construction of natural protected area (NPA) systems is an important initiative to protect biodiversity and maintain the health and stability of natural ecosystems. The Qinghai-Tibet area (QTA) has extremely high ecological value, and the NPAs in this area account for more than half of the NPAs in China. As human activities have intensified, an increasing number of research has been conducted on the NPAs in the region. However, the assessment of the ecological network of the NPAs in the QTA is underexplored. This study assessed the ecological networks derived from the NPA system in the QTA from a "quality-structure–function" perspective. First, the study used the remote sensing ecological index (RSEI) to map the ecological resistance surface of the QTA, generated ecological corridors based on circuit theory, and identified ecological barriers and pinch points in the ecological network to evaluate the quality of the network. Next, the spatial syntax method was used to assess the structural characteristics of the connectivity for the ecological network. Finally, the study analysed changes in the human activity intensity and species population around ecological corridors to quantitatively explore the corridor's biodiversity maintenance function in the context of increased human activity. The findings demonstrated that the ecological network quality of the NPAs within the QTA was generally good. However, some areas such as the Hung River Valley in Qilian-Qinghai Lake were observed to exhibit ecological quality concerns, identified as ecological barrier points. These ecological challenges stem from the competing interests of environmental corridors and the development and utilization of land. In terms of the structural indicators of the ecological network, the closeness of the ecological network in the eastern part of the study area was higher than that in the western part; however, the mean depth shows the opposite pattern, indicating that the northeast has a better overall connectivity than the west. In addition, the intensity of the human footprint and the number of species decreased continuously with increasing distance from the ecological network. However, over the last two decades, a noticeable increase in human footprint intensity has occurred, and the magnitude of this increase grows with increasing distance from the ecological network, indicating that the ecological network is experiencing mounting pressure due to more frequent human activities. However, ecological networks still play a key role in maintaining biodiversity and protecting the ecological environment. The findings of this study could provide a scientific support for protecting the eco-security shield functions in the QTA and globally.