The steppes demonstrate higher productivity but lower diversity in Inner Mongolia than Mongolia: driven by climate or land use?

The steppes on the Mongolian Plateau cover a large land area of Mongolia (MG) and Inner Mongolia of China (IM). They share similar biophysical conditions, but have experienced divergent land use systems over the past several decades. However, no systematic field study has been done across different climate-vegetation zones for a comparison of the patterns of these steppes subject to different land use systems. We performed a field survey on 65 sites along four climatic transects, two in MG and two in IM, across desert steppe, typical steppe and meadow steppe zones, and investigated plant species composition, diversity and productivity. We compared these vegetation features between two regions, and attributed their variation patterns to climate and human activities. The results showed that plant species or plant functional group composition were similar between the two regions. However, plant productivity was significantly higher, whereas plant diversity indices were lower, in IM than MG. Aridity is the primary factor driving the spatial variation in plant diversity and productivity of the steppes across the Mongolian Plateau, while land use also has profound effects. The contrast vegetation pattern between MG and IM may be related with their difference in overgrazing history and grassland management strategies. These results suggest that overgrazing induced decline in plant productivity and its recovery is faster than the species diversity loss and recovery. Our results indicate that land use policies are urgently needed to promote destocking for preventing biodiversity loss in Mongolia, and that practical measures need to be developed to facilitate the recovery of species diversity in Inner Mongolia.