Response of interspecific competition between Stipa purpurea and Achnatherum inebrians to different grazing intensities in an alpine steppe

Competition index, relative crowding coefficient, relative competition severity, and other analyses were used to study the effects of grazing intensity on competition between Stipa purpurea and Achnatherum inebrians in the winter pasture of Gansu Deer Farm located in the middle of the northern slope of Qilian Mountains, China. The competition index of S. purpurea showed a tendency to be initially low before rising and then decreasing slightly based on the grazing intensity gradient, which was largest at 3.45 AUM·ha⁻¹. The competition index of A. inebrians showed a curve change, with an initial rise, followed by a decrease, then a slight increase on the grazing intensity gradient. The competition severity index of S. purpurea and A. inebrians both showed a trend featuring a decrease, increase, and decrease on the grazing intensity gradient. The smallest and largest competition severity index of S. purpurea was 2.45 and 4.85 AUM·ha⁻¹, respectively. The smallest and largest competition severity index of A. inebrians was 1.45 and 3.45 AUM·ha⁻¹, respectively. The relative crowding coefficient of S. purpurea showed a curve change, with an initial increase followed by a slow decrease on the grazing intensity gradient. The relative crowding coefficient of A. inebrians presented a “single peak” curve on the grazing intensity gradient, with a maximum value of 4.85 AUM·ha⁻¹. The competition severity of S. purpurea and A. inebrians was very close at 2.45 AUM·ha⁻¹. Stipa purpurea did not gradually degraded due to the excessively high competitive pressure of A. inebrians, which was conducive to the sustainable grazing and utilization of grassland. The pressing forces of S. purpurea and A. inebrians were both lower at the light grazing intensity (< 2.45 AUM·ha⁻¹); S. purpurea displayed an advantage in the competition. Based on the principle of equal emphasis on economic benefits and sustainable utilization, the suitable grazing intensity is approximately 2.45 AUM·ha⁻¹ for the alpine grasslands in the Qilian Mountains.