Abstract
In the present study, we aim to analyze the effect of grazing, precipitation and temperature on plant species dynamics in the typical steppe of Inner Mongolia, P.R. China. By uncoupling biotic and abiotic factors, we provide essential information on the main drivers determining species composition and species diversity. Effects of grazing by sheep were studied in a controlled experiment along a gradient of seven grazing intensities (from ungrazed to very heavily grazed) during six consecutive years (2005–2010). The results show that plant species composition and diversity varied among years but were little affected by grazing intensity, since the experimental years were much dryer than the long term average, the abiotic constraints may have overridden any grazing effect. Among-year differences were predominantly determined by the abiotic factors of precipitation and temperature. Most of the variation in species dynamics and coexistence between C3 and C4 species was explained by seasonal weather conditions, i.e. precipitation and temperature regime during the early-season (March-June) were most important in determining vegetation dynamics. The dominant C3 species Stipa grandis was highly competitive in March-June, when the temperature levels were low and rainfall level was high. In contrast, the most common C4 species Cleistogenes squarrosa benefited from high early-season temperature levels and low early-season rainfall. However, biomass of Stipa grandis was positively correlated with temperature in March, when effective mean temperature ranges from 0 to 5°C and thus promotes vernalization and vegetative sprouting. Our results suggest that, over a six-year term, it is temporal variability in precipitation and temperature rather than grazing that determines vegetation dynamics and species co-existence of grazed steppe ecosystems. Furthermore, our data support that the variability in the biomass of dominant species, rather than diversity, determine ecosystem functioning. The present study provides fundamental knowledge on the complex interaction of grazing – vegetation – climate.
Highlights
Sustainable grazing management of semi-arid grassland ecosystems requires holistic knowledge about vegetation dynamics and their responses to varying climatic conditions and grazing intensity in order to understand the causes of change in species composition of plant communities
The Effects of Grazing Intensity and Years The aboveground biomass of dominant species L. chinensis significantly decreased with increased grazing intensity, while other investigated species and species diversity parameters were not significantly affected by grazing intensity (Table 1)
Grazing Effect on Species Composition in Steppe the dominant C3 grass S. grandis was two-fold higher in the final year 2010 compared with the first experimental year of 2005, whereas the biomass of the C4 species C. squarrosa and C3 species A. sibiricum decreased by 83% and 60% respectively
Summary
Sustainable grazing management of semi-arid grassland ecosystems requires holistic knowledge about vegetation dynamics and their responses to varying climatic conditions and grazing intensity in order to understand the causes of change in species composition of plant communities. In semi-arid grassland ecosystems climatic factors are the main drivers that determine plant growth and species dynamics [12,13,14]. C4 species are presumably disadvantaged relative to C3 species in their ability to utilize early spring water resources [19]. In this context, the effects of within-year variation in precipitation and temperature, as well as the interaction between these two abiotic factors, are still not fully understood
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