Identifying Man-land Relationship Areal Types and Nonlinear Thresholds: A Case Study of Qinba Mountainous in Southern Shaanxi, China

The man-land relationship and its dynamics were core themes in modern geography. Complex interactions exist between the natural environment and human activities. However, current research focused on the impacts of human activities on ecosystems, ignoring the linear or non-linear characteristics and interaction thresholds. In this study, multi-source data and self-organizing feature map (SOFM) were used to classify man-land relationship areal types in southern Shaanxi, China from 2000 to 2020. The constrain lines method was employed to identify the interaction thresholds between human activities intensity (HAI) and various natural indicators. Results showed that: 1) higher and high natural environment index (NEI) accounted for more than 75% of the southern Shaanxi. 2) Low and lower HAI covered over 85% of the total area, with significant decreases and significant increases in HAI occurring in 45.61% and 24.53% of the study area, respectively. 3) The agricultural type decreased in southern Shaanxi, while the urban and comprehensive type increased. 4) There was a negative convex relationship between HAI and NEI. Thresholds for the effect of HAI on habitat quality were 0.67, 0.37, and 0.64 in the Qinling Mountains, Hanjiang Basin and Daba Mountains, respectively. This study emphasizes that one or more thresholds should be considered for ecological restoration and human management in different regions. This study provided a new perspective for understanding the complex man-land relationship in underdeveloped mountainous regions and offered strong support for coordinating ecological protection with socio-economic development.