Aboveground Biomass and Importance Value of Constructive Species in Desert Steppe Are Co-Regulated by Grazing Intensity and Climate

Constructive species are the creators and constructors of plant communities, exerting significant control over community structure and environmental formation. This study investigates the effects of grazing intensity on the biomass and importance value of the constructive species in a desert steppe and its contribution to community biomass. This study conducted a 5-year monitoring on a long-term grazing experimental platform in desert grasslands. The experiment set four grazing intensities, and from May to September each year, the aboveground biomass, plant height, density, and community biomass of the community were measured. Results showed that different grazing intensities altered the importance value and aboveground biomass of Stipa breviflora, which were regulated by rainfall and temperature during the growing season. In years with higher rainfall, the importance value was relatively low, whereas in years with higher average growing season temperatures, the importance value was higher. In dry years with less rainfall and higher temperatures, the importance value of S. breviflora under moderate and heavy grazing approached 1, significantly greater than that under control and light grazing. The effects of grazing intensity on biomass varied across years. In the wet year of 2016, aboveground standing crop increased with grazing intensity, while in dry years (2017) and average rainfall years (2018 and 2019), the trend reversed. Furthermore, compared to the control, light, moderate, and heavy grazing increased the contribution rate of S. breviflora aboveground biomass to community biomass. The study concludes that constructive species in desert steppes exhibit greater adaptability and growth advantages under the dual pressures of climate variability and grazing, which intensifies competition with other plants and makes the desert steppe more vulnerable. This phenomenon intensifies with increasing grazing intensity. Therefore, the study suggests that light grazing management in desert steppes is beneficial for adapting to future climate variability and challenges.