The muskox (Ovibos moschatus), a key species in the arctic tundra, is the only large-bodied herbivore in Northeast Greenland. At Zackenberg, muskoxen can be found in some of the highest densities in the world. Consequently, a significant grazing pressure of muskoxen is expected there.
In addition, the impact on the nutrient budgets may be even larger, as herbivores tend to feed on plant parts that are rich in nutrients, and they may also redistribute nitrogen and other nutrients through defecation and urination across the landscape.
This study quantify the biomass removal and nitrogen relocation by muskoxen during the snow-free period in the years 1996 to 2013 in the high arctic tundra ecosystem at Zackenberg, Northeast Greenland. By doing this, we aim at not only quantifying the muskox as a key herbivore, but also its role as redistributor of nutrients.
Muskoxen removed almost negligible amounts of the available forage, with under 1% during the summer. However, the muskoxen redistributed large amounts of nitrogen between vegetation types. Muskoxen at Zackenberg forage mainly in the graminoid-dominated areas, but defecate primarily in Salix snowbeds, resulting in net nitrogen transfers from the nitrogen-rich wet habitats to the nitrogen-poor, drier habitats in the same magnitude as the dissolved inorganic nitrogen pool in similar arctic soils. Hence, while the quantitative impact of muskox biomass removal seems negligible, its role as a nitrogen carrier in a nitrogen limited ecosystem is likely to have a significant impact on tundra communities. The results thus stress the central role of muskoxen in the tundra ecosystem.
Reference: Mosbacher JB, Kristensen DK, Michelsen A, Stelvig M, Schmidt NM. (2016) Quantifying muskox plant biomass removal and spatial relocation of nitrogen in a high arctic tundra ecosystem. Arctic, Antarctic, and Alpine Research 48:229-240
Picture: Muskox grazing (photo: Jesper Mosbacher)