Self-stabilizing maintenance process in plant communities of alpine meadows under different grazing intensities

Backgrounds

Grazing prohibition and reduced grazing intensity, as two important “vegetation close-to-nature recovery” methods, have been suggested as economical and effective technologies for enhancing forage production. However, numerous studies have found that the yield of forage could be increased by removing or reducing grazing in a short time in some steady stage of alpine Kobresia meadows, but not in others. To reveal the mechanism behind this phenomenon, we proposed a series of experiments.

Methods

We monitored the plant and soil characteristics in the key steady stages of Kobresia meadows under reduced and prohibited grazing conditions in the same geographic and climatic environments in the northeastern Qinghai-Tibet Plateau for 6 years. We estimated the relationships between the plant community and soil nutrients and obtained the following results.

Results

All measured variables were positively correlated with each other. The plant community structure had higher path coefficients to aboveground biomass, soil organic matter, total nitrogen, and nitrate nitrogen than to other factors. The plant community structure played an important role in response to grazing intensity. Different plant functional groups (PFGs) had different responses to grazing intensity, which led to plant community re-establishment or re-organization under different grazing intensities. Poaceae and Kobresia were more sensitive to grazing intensity than other PFGs, and the ratio of Kobresia biomass (including Kobresia humilis and Kobresia pygmaea) to the total biomass of Poaceae and Kobresia could be used as an indicator of regime shifts within plant communities. With Kobresia pygmaea as the dominant species, the prohibition of grazing was not an efficient approach to increase the yield in the steady stages because this treatment needed more time to recover aboveground biomass. If Poaceae is the dominant PFG, grazing should only be prohibited for 3 years in the steady stages because the aboveground biomass will decrease if grazing is prohibited for more than 3 years.

Conclusions

Therefore, the different steady stages of alpine meadows require different recovery methods to increase recovery efficiency and speed.