Heavy grazing led to the decrease of competitive intensity relationships among dominant populations of clustered grasses in a desert steppe

Abstract

Abstract AimsDesert steppe is an important ecological barrier in northern China. Stipa breviflora and Cleistogenes songorica are the dominant species in the desert steppe. Both plant populations undergo plant cluster fragmentation to varying degrees when subject to grazing interference. However, when both plant populations are present in the same plant community, changes in their inter-specific relationship under grazing is important for regulation of the plant community and its functions. MethodsThis study investigated S. breviflora and C. songorica in a desert steppe, and used variance analysis, the Jaccard index and simple linear regression model analysis methods to study differences in the density of both species under four grazing intensities (i.e., control (CK) 0 sheep·hm-2·half year-1, light grazing (LG) 0.93 sheep·hm-2·half year-1, moderate grazing (MG) 1.82 sheep·hm-2·half year-1 and heavy grazing (HG) 2.71 sheep·hm-2·half year-1) at six scales (i.e., 5 cm×5 cm, 10 cm×10 cm, 20 cm×20 cm, 25 cm×25 cm, 50 cm×50 cm and 100 cm×100 cm). The study explored the competitive relationships between the plant populations. ResultsResults showed that grazing changes the relationship between dominant species. As grazing intensity increases, the competitive abilities of S. breviflora and C. songorica first increased and then decreased. Under heavy grazing conditions, the dominant populations of clustered grasses in the desert steppe resisted interference from high-intensity grazing by reducing inter-specific competition. ConclusionsAs grazing intensity increased, the densities of S. breviflora and C. songorica increased, and the increase became more obvious as the scale of analysis increased.