Maintenance of a desirable mixture of shrubs and grasses is a key issue in sustainable grazing management. The aim of this study was to explore the effect of long-term sheep grazing on desert steppe shrubs. Based on a long-term controlled sheep stocking rate experiment in a desert steppe of north China, combined with long-term random sampling monitoring of above-ground vegetation standing crop (14 years) and short-term systematic sampling monitoring of vegetation cover and individual characteristics of shrubs (3 years), we analyzed plant community changes, the current situation of shrubs and the response of individual shrub characteristics to stocking rate. We found that low stocking rates have increased the cumulative above-ground standing crop of shrubs and herbaceous plants, but the cumulative above-ground standing crop of shrubs under high grazing rates tends to be flat. The cover and height of four shrub species generally showed a decrease with increasing stocking rate, while the response of the four shrubs to the stocking rate gradient varied. Among four shrub species, Artemisia frigida was the most sensitive to stocking rate, followed by Ceratoides latens and Caragana microphylla, while Kochia prostrata was relatively insensitive to stocking rate. These results suggest that grassland managers can use an appropriate stocking rate to maintain desirable plant community composition and configuration in the temperate grassland.
Passive restoration (without any intervention) has been proposed as an effective strategy for degraded cropland restoration. However, whether the vegetation in abandoned cropland can change towards the desired state and the time needed to reach a stable state are still uncertain. We investigated three abandoned croplands with different recovery times (5, 15 and 20 years) and one natural grassland in each of two different types of grassland (desert steppe and typical steppe) in the agro-pastoral ecotone of northern China to assess the restoration potential of abandoned cultivated grassland. Above- and below-ground productivity as well as species biodiversity increased gradually with increasing recovery time. After 20 years of restoration there was no significant difference between abandoned cropland and natural grassland in the typical grassland site, but above- and below-ground productivity and species biodiversity were still lower in abandoned cropland in the desert steppe site. At the beginning of restoration, the communities were dominated mainly by annual species, especially in the desert steppe. As recovery time increased, the biomass and richness of perennial grasses and forbs increased significantly and replaced annual species as the dominant species. In both desert steppe and typical grassland, species similarity between restored and natural grassland increased over time, suggesting that previously cultivated grassland recovered towards the desired state. Our results indicate that 20 years was long enough for the restoration of previously cultivated grassland in the typical steppe, but more time may be needed in the desert steppe.