Satellite and ground-based study on the spatial characteristic of grazing step terracettes in semiarid grassland of Mongolia

Mongolia is located in northeastern Asia, and approximately 75% of its total land area consists of cold, semiarid grassland that is subjected to grazing throughout the year. The flights of closely spaced terracettes marked on the steeper hillslopes (20° <) are common feature throughout the sloping grasslands in Mongolia. These landforms, known as grazing step terracettes, may be erosive trails made by livestock tramping. In this study, satellite and ground-based survey were conducted to investigate the spatial characteristic of grazing step terracettes in the Kherlen River Basin. The analysis of Cs-137 inventories in surface soil within two small grass watersheds with different grazing conditions indicated that net soil loss has occurred on the hillslope with grazing step terracettes. Transect survey of critical slope gradient of grazing step terracettes indicated that grazing step terracettes distributed on the steep slopes (20° <) in the moderately-grazed site, whereas those in the overgrazed-site were found on the gentler slopes (10° <). Furthermore, a satellite approach for estimating the spatial distribution of grazing step terracettes was developed and implemented to the Kherlen River Basin to assess the critical slope gradient of grazing step terracettes. These results suggested that the spatial pattern of grazing step terracettes may help to identify geomorphological indicator of overgrazing and associated soil erosion on the grazing grasslands.