Daurian Pika ( Ochotona dauurica) are steppe-dwelling burrowing mammals with the potential to have large effects on central Asian grasslands due to their extensive range, propensity to occur at extremely high density, and roles as ecosystem engineers and important prey species. The few studies that have been done are mostly from northern China and Russia, while little research has been done in the majority of their range in Mongolia. We studied a population of Daurian Pika in the Darhad Valley of northern Mongolia, near the southern edge of the permafrost, where climate change is progressing rapidly. We evaluated pika populations at 87 random plots across a large 40 x 125 km area and assessed the impact of factors related to vegetation cover, grazing, and soils that predicted their occupancy and an index of their density (number of active burrows). We found that pikas were more likely to occur in areas with taller grass and higher forb cover, and burrow densities were higher in areas with low or moderate grazing and lower soil moisture. In summer, pikas mainly foraged on grass compared with forbs-while in fall, forbs appeared to be selected for in haypiles. Dense pika burrow systems had taller grasses and forbs in their immediate vicinity, suggesting that in some cases, pika could help promote plant growth for other grazers. Long-tailed Ground Squirrel (Urocitellus undulatus) was the second most abundant small mammal in our study sight and selected for areas with high cover of overgrazing indicator species and for short forbs, providing little evidence for competition with Daurian Pika. Our results suggest that shorter grass (similar to 1 cm) can decrease pika occupancy by 75%, while heavy grazing may decrease burrow density by 66% in dry soils. With grazing pressure in Mongolia increasing dramatically since the 1990s, future research is strongly needed to assess the impacts of grazing on this keystone species.

Exploring alpine vegetation dynamics and its driving factors help to predict changes in hydrothermal circulations at high elevations in the future. Currently, there is a lack of systematic research on this topic in the permafrost regions at a basin scale. Spatiotemporal variations of vegetation pattern and growth estimated from satellite remote sensing images at a 30 m spatial resolution on the Google Earth Engine cloud platform were investigated in the Shule River headwater region from 2000 to 2021. The results showed shrinking trends in alpine grassland (AG) and wetland (AW) area, while an expanding trend in alpine desert (AD) area. AD moved to lower altitudes and occupied AG and AW area, possibly owing to mountain permafrost degradation and extreme precipitation. Vegetation patches became fragmented and complex, reflected by increases in patch number and shape index. Vegetation growth, as approximated by the normalized difference vegetation index (NDVI), increased significantly in 42 % of the vegetated area (p < 0.05), particularly in river valleys. In addition, NDVI was negatively correlated with solar radiation over 30 % of the vegetated area (p < 0.05). At the regional scale, vegetation NDVI was positively correlated with root-zone soil moisture and grazing intensity (p < 0.05). The findings suggested that AG and AW at their upper limit of distribution were vulnerable to soil erosion, and the inter-annual variation of vegetation growth was affected by soil moisture and grazing. Moreover, future climate warming may cause alpine vegetation decline by increasing active layer thickness in the absence of adequate precipitation supply.

The melting of permafrost and the degradation of alpine meadow ecosystems caused by climate warming and high-intensity human activities have imposed serious threats to local and global ecological security. In order to estimate the effects of climate warming and grazing interference on the photosynthesis and respiration of alpine meadow plant community in permafrost regions, warming - infrared radiator is applied to simulate the climate warming (increasing temperature by +2 degrees C). The winter grazing level is simulated by mowing the aboveground biomass of all plants. The responses of permafrost meadow community in terms of photosynthesis, respiration, surface soil temperature and moisture, as well as the carbon balance to simulated different climate warming and grazing level were analyzed and discussed. The results showed that: (1) the surface soil temperature in climate warming and grazing plots is significantly higher than in Ck plots (P< 0.01); (2) warming and warming + grazing plots enhanced community photosynthesis and respiration (P< 0.01); (3) warming and warming + grazing treatments increased community aboveground biomass (P< 0.05); (4) the photosynthetic rate increased in the second year, then decreased in the third year when both temperature and grazing level increased during the growing season. However, the ecosystem respiration increasingly increased year by year; (5) compared with the control groups, warming and grazing treatments resulted in an increase in carbon sequestration of the permafrost meadow community during the growing season.