Can vegetation breakpoints in Eastern Mongolia rangeland be detected using Sentinel-1 coherence time series data?

Mongolian society and food production depend heavily on livestock farming, which is usually practiced through nomadic systems. Consequently, movement patterns of herders are crucial in respect of finding sufficient forage and sustainable use of pastures. Since vegetation presumably changes after livestock pasture use, this study hypothesizes that changes in Interferometric Synthetic Aperture Radar (InSAR) data over time are linked to herder and livestock mobility. In this study, a combination of InSAR, optical, and weather time series data has been explored as a tool for spatio-temporal grazing monitoring. To detect movement patterns, a new random forest-based method to detect breakpoints in vegetation condition has been developed and compared to the widely used Breaks For Additive Season and Trend (BFAST) algorithm. In contrast to BFAST, the new method accounts for vegetation changes caused by weather events such as snow and rainfall. The results have been validated using test sites spread across the entire eastern Mongolian steppe ecosystem, covering different rangeland use intensities. The results indicate that (1) random forest performed better than BFAST, indicating that random forest is able to separate vegetation changes caused by grazing from those caused by natural events. ... mehrHowever, the detection was challenging especially for winter movements (for summer camps, random forest and BFAST detected 44% and 28% of movements, respectively). (2) Breakpoints in summer pastures mainly occurred from April to June, while on winter pastures, they emerged in October, November, and the following February and March. The breakpoints in October and November can be explained by increasing grazing pressure as the herders moved to the winter camps while those occurring in spring are associated with enhanced vegetation growth after herders left for summer camps. (3) From a spatial perspective, the random forest model predicts summer and winter pastures with homogeneous patterns. In areas with higher productivity and higher grazing pressure, the summer pastures are located along the rivers while the winter pastures are in the surrounding mountainous areas. This is in agreement with the general movement patterns. In drier and less intensively used areas, the predicted pattern agrees less with the known movements. Consequently, there is insufficient evidence to definitively attribute the occurrence of pasture breakpoints solely to herder movements especially in the eastern and southern parts of the eastern Mongolian steppe ecosystem.