Grazing Intensity and Ecosystem Processes in a Northern Mixed-Grass Prairie, Usa

Abstract

The objective of this study was to evaluate for an 8‐yr period the ecosystem‐level impacts of no grazing vs. sustained moderate and heavy cattle grazing in terms of: (1) plant species basal cover, density, and composition; (2) aboveground net primary production (ANPP), N content of ANPP (ANPP‐N), belowground net primary production (BNPP), and N content of BNPP (BNPP‐N); (3) litter and root decomposition and N loss; and (4) soil C, total soil N, and net in situ soil N mineralization. Moderate and heavy grazing treatments were designed to achieve an end‐of‐the‐grazing‐season residual vegetation of 50% and 10%, respectively, of the long‐term average ANPP of comparable ungrazed sites. The main factor affecting the vegetation response was the increase in precipitation after the drought of 1988; few differences were due to grazing intensity. The total absolute basal cover of grasses increased steadily in all treatments, from an average of 4% during the drought of 1988 to 14% in 1993. Forb density and diversity increased from 51 plants/m2 and 14 species in 1988 to 412 plants/m2 and 36 species in 1995. Grazing, however, increased the relative composition of Poa pratensis and Achillea millefolium, but reduced the relative composition of Bouteloua gracilis and Aster ericoides. ANPP and ANPP‐N were correlated with rainfall, but not with grazing intensity. Heavy grazing led to declines in standing dead biomass, litter, peak root biomass and biomass‐N, root N concentrations, and in situ net soil N mineralization. There was an increase in root decomposition and N loss with grazing. From this study, we reached the following conclusions about the northern mixed‐grass prairie: (1) climatic variations, in particular droughts, control major trends in plant species composition and production, with grazing playing a secondary role; (2) heavy grazing leads to declines in standing dead biomass and biomass‐N, litter biomass and biomass‐N, peak root biomass and biomass‐N, and in situ net soil N mineralization, which may have a significant long‐term impact on range condition; and (3) grazing pressures that lead to a removal of 50% of ANPP, however, seem to be sustainable and compatible with the maintenance of range condition.

Effects of grazing exclusion on carbon sequestration and plant diversity in grasslands of China—A meta-analysis

“…Livestock grazing is a pivotal issue affecting plant growth, species diversity and soil carbon accumulation in grasslands (Olff and Ritchie, 1998;Watkinson and Ormerod, 2001;Piñeiro et al, 2010;McSherry and sity. For carbon sequestration, some studies found that grazing exclusion facilitated vegetation recovery, increased plant productivity and thus enhance soil carbon stocks in degraded grasslands (Biondini et al, 1998;McIntosh and Allen, 1998;Li et al, 2008;Mekuria et al, 2007;Mekuria and Veldkamp, 2012;Xiong et al, 2014). Others, however, reported no change (McNaughton et al, 1998;Pucheta et al, 2004) or even decline of carbon stocks in grasslands (Schuman et al, 1999;Leriche et al, 2001;Frank et al, 2002;Wienhold et al, 2001).…”

The response of a shrub‐invaded grassland on the Inner Mongolia steppe to long‐term grazing by sheep

“…In North America, medium levels of grazing by bison (Hartnett et al 1996;Collins et al 1998) and cattle (Collins 1987) increased species diversity on tallgrass prairie, and medium grazing by cattle increased plant diversity on mixedgrass prairie (Biondini et al 1998) and shortgrass steppe (Milchunas et al 1990(Milchunas et al ,1992Hart 2001). In contrast, very heavy grazing that removed 90% of aboveground biomass reduced species diversity on mixed-grass prairie (Biondini et al 1998).…”

Investigating vegetation biophysical and spectral parameters for detecting light to moderate grazing effects: a case study in mixed grass prairie

“…It is hard to find intact reference sites for grazing studies as most grasslands experience disturbances. Finally, although primary knowledge of light to moderate grazing impacts on mixed grasslands in many other regions is known [28][29][30], the impacts of grazing on this area have not been quantitatively measured and our knowledge about the characteristics of grasslands in this area is very limited.…”