Mechanism of grazing and climate interaction on vegetation diversity
Grazing and climatic factors have interactive effects on vegetation diversity in arid and semi-arid regions, that is, one driver can change the effect of the other driver on the state variable. We discuss the mechanisms and causes of the discovered interaction effects from the perspective of vegetation community stability. With climate change, grazing may reduce vegetation stability. However, under no grazing and low grazing intensity, vegetation coverage was higher, and surface plants were able to fully reduce water loss due to temperature rise.
Grasslands with higher vegetation coverage have stable water retention capacity and are more resistant to climate change, especially warming. Under the background of high intensity grazing, the surface vegetation is overeaten, the vegetation coverage is greatly reduced, and the water holding capacity of the grassland is reduced. Factors such as soil exposure and temperature increase will accelerate surface water evaporation, reducing the available water for plants. An increase in precipitation does not effectively increase surface water supply to plants. By affecting water supply, high-intensity grazing makes vegetation more sensitive to temperature changes and reduces the stability of vegetation communities.
In addition to the environment, the characteristics of plants are also important internal factors that determine their survival. The survival and anti-interference ability of plant species were different under different climate patterns. For example, in arid climates, high-individual plants were more significantly affected by grazing, indicating that high-individual plants were less resistant to grazing disturbance when the climate was drier. In addition, in humid DL and HL, grasses were more sensitive to grazing. Although the coverage of grasses decreased significantly, the coverage of low-height plants did not decrease, and high-height plants were least affected by grazing in this climate model (Figure 7). The results showed that humid climate was conducive to niche succession among species. Although the number of tall grass plants decreased, other tall plant populations quickly occupied the niche, which reflected the higher stability of plant communities in humid climate. The results show that the increase of precipitation in the rainy season plays a greater role in maintaining vegetation stability, while the role of temperature change is very limited. Moreover, a severely dry climate would weaken the resistance of plant communities to grazing and amplify the negative effects of grazing, while a transition to a wetter climate model would increase the stability of plant communities and make them less susceptible to grazing.