Did a meta-analysis accurately estimate the temporal trends of carbon stock change after grazing exclusion in China's grasslands? A comment on "Effects of grazing exclusion on carbon sequestration in China's grassland," by Deng et al. (2017)

The temporal pattern of carbon stock changes in response to grazing exclusion (GE) is important for grassland ecosystem restoration policy. The carbon stock change rate is the quotient computed by dividing the change in carbon stock after GE by GE duration. We modeled varying carbon stock change rates with GE durations based on data from a meta-analysis by Deng et al. (2017). We found that the close relationship between the carbon stock change rate and GE duration was mostly driven by GE duration in the denominator, rather than by carbon stock changes in the numerator. We argue that Deng et al.'s conclusion that the exponential decay trend varies with GE duration was inaccurate and that it was misleading to suggest there is a temporal pattern to carbon stock changes that is associated with GE duration. Their model may further encourage GE-based policy that includes fencing as a major practice of grassland restoration. However, this practice yields clearly negative impacts on herders' livelihoods, animal husbandry, pastoral social development and wildlife protection.