Abstract:

Aims Human disturbance, such as overgrazing have resulted in widespread declines in biodiversity and ecosystem functioning and services in arid and semiarid grasslands worldwide. This study is aimed to examine the effects of grazing intensity, topography and precipitation fluctuation on plant diversity across three levels of organization (i.e., plant species, functional group, and community) in a typical steppe of the Inner Mongolia grassland.
Methods Based on a long-term grazing experiment maintained for eight years with seven levels of grazing intensity and two topographic systems in a typical steppe of the Inner Mongolia grassland, the effects of grazing intensity, topography (flat vs. slope), and precipitation fluctuations (wet vs. normal years) on plant diversity (i.e. α, β and γ diversity) and their controlling mechanisms were examined.
Important findings Our results showed that: (1) The diversity-grazing intensity relationship differed between two topographic systems and over two years (wet vs. normal years). The α, β, and γ diversity in the wet year (2012) were higher than those in the normal year (2011). The effect of topography on plant diversity was dependent on precipitation, with higher α diversity in the slope system and normal year and higher α and γ diversity in the flat system and wet year. There was no significant effect of topography on β diversity. (2) The α diversity decreased with increasing grazing intensity in both the flat and slope systems. The α diversity response to grazing differed substantially among the dominant species, common species, and rare species in the two topographic systems, with the highest negative response for rare species, intermediate negative response for common species, and the weakest response for dominant species. (3) In the flat system, γ diversity declined with increasing grazing intensity, while it firstly decreased and then increased at the intermediate level of grazing intensity in the slope system. (4) The β diversity decreased with increasing grazing intensity in the flat system due to grazing-induced species convergence, while it did not show any tendency in the slope system. Our results suggest that the topography and precipitation are two key factors governing the relationship between plant biodiversity and grazing intensity in the arid and semiarid grasslands. The loss of species in the dry year was greater in the flat system than in the slope system, while the opposite result was found in the wet year. The rare species plays an important role in maintaining species diversity. These findings provide a better understanding of the biodiversity-grazing intensity relationship in the context of different precipitation and topographic conditions in the semiarid steppe and beyond.

Key words: α diversity, β diversity, γ diversity, grazing intensity, topography, precipitation fluctuation, typical steppe