The effects of grazing on shrub expansion depend on species' palatability and long- term alterations in propagule banks in an alpine meadow
| 作者 | Shilin Wang，Wenxia Cao，Ruzhen Wang，Jinlan Wang，Wen Li，Jianhui Huang，Guoxiang Niu |
| 刊物 | Journal of Applied Ecology |
| 标识符 | 10.1111/1365-2664.70201 |
| 摘要 | 1. Shrub expansion is commonly observed in grassland ecosystems under climate change. In these systems, palatability is considered an important factor shaping plant community dynamics, particularly under grazing management. However, direct evidence remains limited regarding the effects of grazing and shrub palat-ability on shrub expansion in alpine meadows, particularly from the perspective of propagule bank dynamics. 2. We conducted a field experiment on the Qinghai–Tibetan Plateau to quantify the direct and indirect impacts of grazing and shrub palatability on the shrub expan-sion of six dominant shrubs from 2013 to 2021. We quantified shrub palatability and characterized species composition and density of the community's soil seed bank and bud bank. 3. Grazing reduced the shrub expansion rate from 12% to 3% compared to non-grazed plots, largely due to decreased expansion of high- palatable shrub species in grazed plots. Specifically, the annual expansion rates of highly palatable shrubs Salix rehderiana and Dasiphora fruticosa were −0.99% and −0.33%, respectively, in the grazed plots, but 1.8% and 0.3% in the nongrazed plots. Compared to the highly palatable shrubs, grazing was less effective in controlling the annual ex-pansion rates of medium- palatability shrubs (Spiraea alpina and Caragana jubata) and did not affect low- palatability shrubs (Rhododendron capitatum and R. thymi-folium). Grazing significantly increased the soil seed bank densities under the canopy of high- palatable shrubs, but significantly decreased their shrub bud bank densities. The piecewise structural equation models showed that the main fac-tors regulating the shrub expansion rate were shrub palatability and bud bank in grazed plots. 4. Synthesis and applications: Effects of grazing on shrub expansion varied with shrub species' palatability and were jointly controlled by long- term alterations in propagule banks in alpine meadows. Grazing intensity at 6.0 Tibetan sheep/ha, which is the current rotational grazing system in the Qinghai–Tibetan Plateau, could not reverse the trend of shrub expansion, but could reduce the rate of shrub expansion. Therefore, it may be beneficial for grassland managers and policymak-ers to take shrub palatability into account when developing grazing strategies to manage shrub expansion in grassland. |
