Aims Grazing, as one of the important biological driving factors, plays a key role in the spatial heterogeneity of grassland plant community. Large herbivores can affect the spatial heterogeneity of grassland plant community by foraging, trampling and excreting dung. At the same time, plant community height is a key parameter to describe the structure of grassland. However, little attention has been paid to exploring the spatial heterogeneity of plant community height under different herbivore assemblages. Aim to this issue, this work examined the response of the spatial heterogeneity of plant community height to different herbivore assemblages in Horqin sandy grassland, which is helpful to better understand the importance of grazing in maintaining spatial heterogeneity of grassland plant community and promote grassland animal biodiversity.
Methods An experiment was conducted with four grazing treatments, including no grazing (NG), cattle grazing (CG), sheep grazing (SG) and mixed grazing (MG) of cattle and sheep. We established two perpendicular 15 m transects crossing at the centre point of each plot to reduce the variation caused by environmental gradient. Along the two transects, samples were taken from 0.25 m × 0.25 m quadrates with 0.5 m space interval, and totally 244 sampling points were measured. We used traditional and geostatistical methods to analyze the data from different grazing treatments.
Important findings Results showed that the mean of plant community height in our study plots satisfied the following ranking: SG (38.86 cm) > NG (21.01 cm) > MG (17.29 cm) > CG (13.36 cm). The coefficient of variation of all treatments had moderate level, and the variation range was 37.82%-66.97%, followed by NG > MG > CG > SG. According to the optimal model fitting by the parameters of semi-variance function, NG, MG, CG and SG corresponded to spherical model, exponential model, linear model and linear model respectively, and the structural proportion satisfied MG (82.7%) > NG (80.3%) > SG (40.2%) > CG (39.1%). Furthermore, Kriging interpolation and fractal dimension were used to analyze the spatial pattern of plant community height. It clearly showed NG had a patchy spatial distribution of plant height, MG could maintain the patchy spatial pattern, and CG and SG homogenized the spatial pattern. The fractal dimension value (D0)of each grazing treatment was close to 2, which indicated the spatial structure of four treatments was good with simple spatial pattern. Thus, mixed grazing of cattle and sheep could maintain plant community structural heterogeneity, while the single grazing of cattle or sheep would reduce the spatial heterogeneity. Our findings shed novel light into management of mixed grazing of cattle and sheep, which should be adopted to maintain the spatial heterogeneity of grassland plant community in Horqin sandy grassland.