Grazing intensity in grassland ecosystems: implications for carbon storage and functional properties

Grazing lands cover more than one-third of the terrestrial land surface and are still expanding. The intensity of grazing is also growing with time due to the increase in the number of animals per unit of land or the duration of herbivory. Changes in grazing intensity exert strong pressure on ecosystem functioning, including carbon (C) sequestration. Grazing response to ecosystem C retention can be explained by the changes in biogeochemical processes that regulate C fluxes. Here, we summarized the ecosystem functional properties that affect C storage in grasslands as a result of changing grazing intensities. We synthesized 151 published studies globally and discussed the changes in different ecosystem functional property responses to grazing. High-intensity grazing mostly decreased C storage while light- to moderate-intensity grazing optimized the trade-offs between C sequestration and animal production. The synthesis showed that 86% of the studies reported either an increase or no change in SOC stocks under light grazing while under heavy grazing, 74% of the studies reported a significant decrease in SOC stocks. We also discussed the changes in ecosystem functional properties whereby grazing affects C sequestration. Some of them include: the changes in net primary productivity, soil organisms, enzymatic activity, soil respiration, and the complex interactions of these processes with climate change. Grassland management practices should be ecosystem-specific to ensure optimum production and enhance C sequestration. It is also important to understand the time factor (hysteresis), especially on how long it takes to sequester a certain amount of C from grassland management practices.