Reply to Liang and Gornish: Climate and livestock grazing jointly regulate grassland ecosystem multifunctionality

Climate (e.g., precipitation) and grazing disturbance are 2 important factors affecting grassland biodiversity and ecosystem functions (1). Liang and Gornish (2) argue that we do not consider the precipitation effect as an independent factor in our PNAS paper on diversifying livestock promoting multidiversity and ecosystem multifunctionality (EMF) (3). Here, we clarify that our study was conducted only in a meadow steppe, not across different grassland types over larger spatial scales; that is, all of the grasslands with single and mixed grazing of cattle and sheep were examined under identical climate conditions. Moreover, all grazing treatments were controlled at comparable and moderate grazing intensity. Thus, the observed changes in grassland multidiversity and EMF in our study were the result of grazing livestock treatments and associated species diversity. Our study therefore supports the notion that diversifying livestock grazing at a moderate level can have important ecosystem service benefits in the meadow steppe.

However, we welcome the argument by Liang and Gornish (2) that the effects of livestock grazing on biodiversity and ecosystem functions could be dependent on rainfall. Although theory predicts that herbivores enhance plant diversity at high precipitation (resulting in high productivity) while reducing it at low precipitation (4–7), the positive or negative effects of herbivores in different precipitation sites also strongly depend on grazing intensity and modes. High-intensity grazing still can decrease diversity, even if it’s at a high-precipitation site (8). Koerner et al. (9) synthesized data from 252 herbivore exclusion studies and found that, contrary to theory, herbivory did not decrease species richness at low precipitation. In Liang et al.’s (10) study, the same grazing intensity brings different effects on grassland in dry years and wet years, which is most likely because the controlled grazing intensity is moderate in wet years while it could be heavy in dry years due to drought-induced low productivity. Therefore, moderate grazing intensity should be modified based on precipitation each year for each site. We argue that climate factors and livestock grazing modes jointly regulate grassland multifunctionality.

Undoubtedly, herbivores, as an important biotic component, play an important role in maintaining grassland ecosystem functions, and their effects may or may not vary with productivity and/or precipitation. In human-affected grasslands, we are increasingly concerned about how we might better manage livestock by altering livestock species composition and grazing intensity for different grassland types and climatic conditions to achieve the best outcomes. Our study shows that, besides controlling optimal and moderate grazing intensity, we could diversify livestock grazing modes to further improve grassland ecosystem multifunctioning. Although our work was conducted in a meadow steppe, based on classical niche theory and diversity theory, we believe that diversifying livestock can lead to diverse disturbance regimes and thus increase environmental heterogeneity, thereby promoting biodiversity and EMF in general grassland ecosystems. Nevertheless, we strongly suggest that the generality of diversifying livestock effects should be empirically tested and demonstrated across different grassland types worldwide in the future, due to the complex interactive effects between grazing and climates.