Effects of Grazing Management on Spatio-Temporal Heterogeneity of Soil Carbon and Greenhouse Gas Emissions of Grasslands and Rangelands: Monitoring, Modelling and Upscaling

Abstract

The sustainability of grazing lands lies in the nexus of human consumption behavior, livestock productivity, and environmental sustainability. Due to fast growing global food demands, many grazing lands have suffered from overgrazing, leading to soil degradation, air and water pollution, and biodiversity losses. Multidisciplinary efforts are required to understand how grazing lands can be better monitored, assessed and managed to attain predictable outcomes of optimal benefit to society. This paper synthesizes our understanding based on previous work done on impacts of grazing on ecosystem goods and services, identifies current knowledge gaps, and formulates a plan forward. We review the impacts of two contrasting grazing systems, continuous and multi-paddock rotational grazing, on soil carbon (C), nutrient cycling and greenhouse gas emissions (GHGs). We then extend our review to explore challenges of incorporating spatial heterogeneity and temporal variability into monitoring and modelling C and nutrient cycling in grazing lands. We revisit two process-based models (i.e., DNDC and DayCent) and two watershed models (i.e., SWAT and VIC) widely used to simulate C, nutrient and water cycles of these lands. Finally we identify research directions for improving the knowledge base which is essential to conserve grazing lands and maintain their ecosystem goods and services.

Multi-year CO<sub>2</sub> budgets in South African semi-arid Karoo ecosystems under different grazing intensities

“…Previous studies determined water availability as the main driver controlling gross primary production (GPP) through increasing photosynthesis and extending the length of the growing season (Ago et al, 2016;Bao et al, 2019;Meza et al, 2018;Otieno et al, 2010;Wang et al, 2019). However, the seasonal responses of GPP and ecosystem respiration (Reco) to precipitation pattern and the impacts of precipitation on the annual carbon budget are less well understood in the South African semi-arid ecosystems.…”

“…Land and vegetation degradation belong to the crucial drivers altering ecosystem-atmosphere carbon exchange. Even though many studies suggest that overgrazing leads to biodiversity losses and soil degradation (Hansis et al, 2015;Kairis et al, 2015), its impact on the ecosystem CO2 exchange is still not well understood as ecosystems may respond differently depending on their grazing history as well as biotic (vegetation cover) and micrometeorological factors (Chen et al, 2014;Gourlez de la Motte et al, 2018;Müller et al, 2007;Richter and Houghton, 2011;Talore et al, 2016;du Toit et al, 2011;Wang et al, 2019).…”