Grazing effects on surface energy fluxes in a desert steppe on the Mongolian Plateau

Abstract

Quantifying the surface energy fluxes of grazed and ungrazed steppes is essential to understand the roles of grasslands in local and global climate and in land use change. We used paired eddy-covariance towers to investigate the effects of grazing on energy balance (EB) components: net radiation (R ), latent heat (LE), sensible heat (H), and soil heat (G) fluxes on adjacent grazed and ungrazed areas in a desert steppe of the Mongolian Plateau for a two-year period (2010-2012). Near 95% of R was partitioned as LE and H, whereas the contributions of G and other components of the EB were 5% at an annual scale. H dominated the energy partitioning and shared ~50% of R . When comparing the grazed and the ungrazed desert steppe, there was remarkably lower R and a lower H, but higher G at the grazed site than at the ungrazed site. Both reduced available energy (R - G) and H indicated a "cooling effect" feedback onto the local climate through grazing. Grazing reduced the dry year LE but enhanced the wet year LE. Energy partitioning of LE/R was positively correlated with the canopy conductivity, leaf area index, and soil moisture. H/R was positively correlated with the vapor pressure deficit but negatively correlated with the soil moisture. Boosted regression tree results showed that LE/R was dominated by soil moisture in both years and at both sites, while grazing shifted the H/R domination from temperature to soil moisture in the wet year. Grazing not only caused an LE shift between the dry and the wet year, but also triggered a decrease in the H/R because of changes in vegetation and soil properties, indicating that the ungrazed area had a greater resistance while the grazed area had a greater sensitivity of EB components to the changing climate.

Grazing alters net ecosystem C fluxes and the global warming potential of a subtropical pasture

“…By removing biomass, grazing could increase albedo due to decreased net radiation as lower green biomass reflects more incident radiation (Shao et al 2017). By removing biomass, grazing could increase albedo due to decreased net radiation as lower green biomass reflects more incident radiation (Shao et al 2017).…”

“…In addition to soil moisture, the production and oxidation of CH 4 are governed by changes in soil temperature, plant productivity, and manure inputs (Whiting and Chanton 1993, Banger et al 2012, Bridgham et al 2013. Grazing could increase net CH 4 emissions from soils by increasing its wetness as a result of biomass removal and decreased transpiration (Bridgham et al 2013, Turetsky et al 2014, Shao et al 2017. Grazing could increase net CH 4 emissions from soils by increasing its wetness as a result of biomass removal and decreased transpiration (Bridgham et al 2013, Turetsky et al 2014, Shao et al 2017.…”

Joint forcing by heat waves and mowing poses a threat to grassland ecosystems: Evidence from a manipulative experiment

“…More importantly, increases in mowing intensity not only have profound consequences for grassland ecosystems (Shao, Chen, & Li, 2013) but can also increase the sensitivity of grassland ecosystems to climate change (Chen, John, Shao, et al, 2015a). Here, we hypothesize that mowing may interact with global warming and reduce ecosystem resilience to extreme weather (Benot et al, 2014) HWs and land use, especially their joint influences on plant morphology, phenology, community structure, and the underlying processes responsible for ecosystem functions.…”

“…). They also influence the microclimate (Shao et al, ) and associated plant traits, such as plant height and specific leaf area (Reisch & Poschlod, ), which in turn will affect plant reproductive phenology (Benot et al, ). More importantly, increases in mowing intensity not only have profound consequences for grassland ecosystems (Shao, Chen, & Li, ) but can also increase the sensitivity of grassland ecosystems to climate change (Chen, John, Shao, et al, ).…”

Grazing effect on grasslands escalated by abnormal precipitations in Inner Mongolia

“…In particular, drought in water-limited ecosystems appears to exacerbate the effects of grazing (Dangal et al, 2016;Eldridge, Poore, Ruiz-Colmenero, Letnic, & Soliveres, 2016). For example, increased grazing intensities can lead to a substantial decline in plant diversity, primary production (Biondini, Patton, & Nyren, 1998;Fetzel, Havlik, Herrero, & Erb, 2017), and resistance (Shao et al, 2017). These negative consequences have also been found for the grasslands extensively (Olff & Ritchie, 1998).…”