Fertilisers mediate the short-term effects of sheep grazing in the Icelandic highlands

Sustainable grazing management in tundra ecosystems is receiving increasing attention. In the Icelandic highlands, past grazing practices have played a major role in the extensive soil erosion, leaving many parts of this tundra rangeland in poor condition. However, the impacts of current grazing practices are not well understood. We measured the short-term effect of grazing by comparing the amount of bare ground and aboveground biomass in grazed and ungrazed plots, with and without fertiliser application, in adjacent dwarf-shrub heaths and sparsely vegetated areas, at two sites within and outside the volcanic active zone. Grazing did not affect the amount of bare ground, but in the fertilised plots grazing consistently reduced plant biomass (mainly graminoids). Fertiliser application can increase grazing intensity, which can counteract the additional biomass accumulation. Consequently, the removal of biomass by sheep needs to be considered when fertilisers are used as part of a strategy to combat erosion.