Abstract
The Mongolian steppes with a long history of nomadic pastoralism cover a large area of the Palaearctic steppe biome and are still relatively intact. As livestock number has increased over the last two decades, grazing has been considered as the main reason of pasture degradation. However, the impact of grazing on vegetation dynamics, and its interaction with climate, is still not clear. We reviewed 44 publications in Mongolian language, covering 109 sites in five main steppe types, i.e., desert, dry, meadow, mountain, and high mountain steppe, with a mean annual precipitation and temperature range from 120 to 370 mm and from −6 to +5°C, respectively. We calculated relative changes in vegetation cover, species richness, and aboveground biomass from heavily grazed with respect to lightly/non-grazed conditions. Multiple linear regression models were used to test the impact of environmental factors, i.e., mean annual precipitation, coefficient of variation for precipitation, mean annual temperature and elevation. Grazing had a stronger effect on the vegetation of dry, desert and high mountain steppes, whereas its effect was less pronounced in the meadow and mountain steppes with mesic climate and high productivity. Vegetation cover, species richness and aboveground biomass were reduced by heavy grazing in the dry, desert and high mountain steppes. In the meadow steppes, grazing reduced vegetation cover, but increased richness and had nearly no effect on biomass. In the mountain steppe, richness and cover were not affected, but biomass was reduced by heavy grazing. Additionally, grazing effects on biomass tended to be more pronounced at sites with higher amounts of annual precipitation, and effects on cover changed from negative to positive as elevation increased. In conclusion, grazing effects in Mongolian steppes are overall negative in desert, dry and high mountain steppes, but no or even positive effects are found in meadow and mountain steppes. Especially, heavy grazing showed a detrimental effect on all vegetation variables in desert steppes, indicating the existence of combined pressure of climate and grazing in arid habitats, making them potentially sensitive to overgrazing and climate change. Grassland conservation and management should consider characteristics of different steppe types and give importance to local environmental conditions.
Highlights
Grasslands cover 41% of the World’s terrestrial surface (White et al, 2000), which sustain livelihoods for nearly 800 million people, and are a crucial source of livestock forage and habitat for diverse wildlife (White et al, 2000)
Grazing effects on aboveground biomass (AGB) were more negative when mean annual precipitation (MAP) was lower, while the magnitude of the effect decreased as MAP increased (Figure 4A); In addition, effects of heavy grazing on vegetation cover (VC) were neutral or even slightly positive at higher elevations, but became predominantly negative at lower elevations (Figure 4B)
In contrast to generally limited or even absent effects on aboveground parts that were found in many other studies in the desert steppes of Mongolia (Fernandez-Gimenez and AllenDiaz, 2001; Wesche et al, 2010; Jamiyansharav et al, 2018) and Inner Mongolia (Bai et al, 2012), we found that species richness (SR) and VC decreased by nearly 40% under heavy grazing
Summary
Grasslands cover 41% of the World’s terrestrial surface (White et al, 2000), which sustain livelihoods for nearly 800 million people, and are a crucial source of livestock forage and habitat for diverse wildlife (White et al, 2000). Most of the world’s grasslands are found in temperate regions, and these temperate grasslands have the distinction of being the most altered terrestrial ecosystems on the planet (Henwood, 2010) and the most threatened globally. Of these temperate grasslands, 19.6% (10.3 million km2) belong to the Palaearctic steppe biome, which forms a vast belt across the mid-latitudes of Eurasia, with nearly 1.3 million km occurring in Mongolia (Henwood, 2010; Wesche et al, 2016). According to a national report on the rangeland health of Mongolia, 58% of Mongolian rangeland areas are estimated to be degraded, of which 14, 21, 13, and 10% are slightly, moderately, heavily and fully degraded, respectively, based on field monitoring data (Densambuu et al, 2018)
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