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

Abstract

The diversity of a degraded grassland community on the Chinese Inner Mongolia steppe dominated by Artemisia frigida (Asteraceae) subject to a range of grazing treatments (zero, and light, medium and heavy grazing) for 13 years was studied from July to August 2002. Under zero grazing, percentage total vegetation cover was significantly (P < 0.05) less than under light, medium, and heavy grazing. Although not dominant in any treatments, percentage cover of Carex duriuscula (Cyperaceae) was higher than other species in the zero, light, and medium grazed treatments. Its cover tended to decline as grazing intensity increased (P = 0.49). Aneurolepidium chinense (Poaceae) reasserted its dominant status in the zero grazed grassland; A. frigida remained dominant under light and medium grazing. Under heavy grazing, Potentilla acaulis (Rosaceae) was the dominant species and it provided the highest percentage cover. Zero and heavy grazing resulted in fewer (three-four) species contributing most of the total cover (cf. six-seven species for light and medium grazing). This was reflected by indices of diversity and evenness, which were highest for light and medium grazing. The Simpson Dominance Index was highest for the zero and heavily grazed treatments, indicating that at the extremes of the grazing spectrum, single species tended to exclude potential co-dominants more effectively than at intermediate levels of grazing. Selective grazing was a key process. Grazing increased the proportion of unpalatable and grazing resistant species, and species that although palatable, were relatively inconspicuous. These findings are discussed in terms of their impact on the productivity and long sustainability of grazing. The need to develop a better understanding of underlying processes, and more sustainable forms of grazing management are highlighted.

Impacts of warming and elevated CO2 on a semi‐arid grassland are non‐additive, shift with precipitation, and reverse over time

“…Within the controls, the progressive decline of C 3 graminoids and rise of forbs, particularly A. frigida, could have been caused by a shift in grazing pressure; biennial clipping during the experiment likely increased vegetation removal compared to pre-experiment conditions, when there was light grazing by cattle and wildlife. This speculation is consistent with other observations that increased grazing intensity can increase the abundance of A. frigida at the expense of C 3 graminoids, particularly in nutrient-poor soils (Gao et al 2005;Liu et al 2006;Liang et al 2009). Thus, in our study, the negative effect of warming on forb abundance might have been mediated by the positive effect of warming on N-availability.…”

Plant diversity consequences of a herbivore‐driven biome switch from Grassland to Nama‐Karoo shrub steppe in South Africa

“…; van Auken ; Watkinson & Ormerod ; Liu et al. ). The negative impacts of shrub encroachment have included steep declines in plant species richness (Báez & Collins ; Knapp et al.…”

“…Shrub invasion or encroachment of grassland and grassy savannah is perceived as an important problem through-out the world (Aguiar et al 1996; van Auken 2000;Watkinson & Ormerod 2001;Liu et al 2006). The negative impacts of shrub encroachment have included steep declines in plant species richness (Báez & Collins 2008;Knapp et al 2008), raised risk of animal species extinction (Spottiswoode et al 2009) and decreased grazing capacity, which has rendered many rangelands no longer economically viable (Smit et al 1999).…”

Effects of Water Addition on Reproductive Allocation of Dominant Plant Species in Inner Mongolia Steppe

“…Tzvel., Stipa grandis P.A. Smirn., Artemisia frigida Willd., and Potentilla acaulis L.] in the Inner Mongolia steppe in China, where L. chinensis is a perennial forage grass with long strong rhizomes, and S. grandis is a perennial tussock grass with closely clumped shoots, while A. frigida and P. acaulis are perennial herbs with stolons and developed adventitious roots (Li et al, 2005;Liu et al, 2006).…”