Title: Patterns and drivers of rangeland degradation in Mongolia

Rangelands are currently facing increasing threats from climate change, overgrazing and land conversion and rangeland degradation is a growing concern worldwide. The ability of degraded rangelands to provide the natural resources needed to sustain pastoralists and ensure the persistence of traditional nomadic lifestyles is less than that of healthy rangelands. In Mongolia, serious concerns have emerged in recent decades about the accelerating rate of rangeland degradation. Understanding rangeland degradation and assessing long term trends of vegetation change is thus critical to design sustainable management practices. Mongolian rangelands represent about 2.5% of the world’s total grassland area and are considered among the last intact rangelands in the world. Most of the Mongolian territory is covered by rangelands and the livelihoods of nearly half of the Mongolian population are related to livestock grazing on rangelands.

The main objectives of this PhD thesis were (1) to compile previous studies on rangeland degradation in Mongolia and systematically review and synthesize information on how studies identified degradation, the theoretical frameworks used, drivers of degradation and the geographical distribution of studies, (2) to detect trends in vegetation change in Mongolian rangelands using broad scale long-term monitoring data, and (3) to investigate the drivers of change in vegetation over ~10 years in the steppe zone of Mongolia using detailed field data.

Trends in the literature indicated growing concerns about rangeland degradation in Mongolia, especially since the turn of the 21st century when the number of international scientific publications on this topic considerably increased. However, the lack of a common definition of degradation and of standardized ways of measuring it makes it difficult to compare results of different studies. Using a nationwide long-term database of rangeland health in Mongolia, we detected mostly non-significant trends in key indicators of vegetation change across the forest steppe, steppe and desert steppe. However, where significant trends were detected, these were consistent with reported rangeland degradation. For example, we observed noticeable decreasing trends in grasses characteristic of healthy rangelands, including Stipa sp. This was the first attempt to use the database of the National Rangeland Monitoring program and the results emphasize the value of this national resource. Using detailed field data, we found that changes in vegetation over a ~10-year period were widespread across the steppe. Plant communities changed from communities dominated by grasses toward communities dominated by annuals and sedges that are characteristic of degraded ecosystem states. However, disentangling the role of different drivers remains difficult. Our results highlight the importance of considering regional differences
in the effect of different drivers on grassland vegetation when designing sustainable grazing management strategies. In all, this study shows that we are still far from understanding the complexities of rangeland degradation. Nevertheless, current efforts are promising, and Mongolia provides a good example for the world.