A review of global wilderness area identification since the 21st century

Wilderness areas are natural landscape elements that are relatively undisrupted by human activity and play a critical role in maintaining ecological equilibrium, preserving naturalness, and ensuring ecosystem resilience. Since 2000, monitoring of global wilderness areas has increased owing to the availability of spatial map data and remote sensing imagery related to human activity and/or human footprint. Progress has been made in the remote sensing of wilderness areas by relying on available historical literature (e.g., published papers, books, and reports). However, to our knowledge, a synthesis of wilderness area research from a remote sensing perspective has not yet been performed. In this preliminary review, we discuss the concept of wilderness in different historical eras and systematically summarize dynamic wilderness monitoring at local, national, and global scales, available remotely sensed indicators, disparities and commonalities in identification methods, and mapping uncertainties. Finally, since this field remains in its initial stage owing to a lack of unified standards and vertical/horizontal comparisons, we present insights into future research directions, particularly with regard to remote sensing. The findings of this review may help to improve the overall understanding of current wilderness patterns (i.e., increases/decreases) and the mechanisms by which they change, as well as provide guidance for global nature conservation programs.