Large herbivores as stabilizing ecosystem engineers in thawing terrestrial Arctic environments

With an increasingly warm Arctic, new challenges arise as Arctic permafrost ground starts to thaw further. Thaw destabilizes the ground and makes soil-stored organic carbon available for microbial decomposition. To reduce thaw intensity, we examined the impact of large herbivorous animals on thaw depth in the seasonal active layer and carbon storage in both the active layer and the underlying permafrost in eastern Siberia. In the Pleistocene Park (Cherskiy, Siberia, 68.512694° N, 161.508736° E), a landscape-scale lifesize long-term experiment on recreating a large-herbivore-driven ecosystem in a 50-ha fenced area is being conducted since more than 20 years. There, we sampled locations with different grazing intensity in drained thermokarst lake basins and Yedoma uplands and analysed these samples for organic carbon content and degree of decomposition. We distinguished between “old” undecomposed organic material and freshly introduced organic material associated with the animal grazing itself. Because of reduced snow depth in winter due to animal trampling, we hypothesize that heavily grazed areas are affected by a shallower thaw depth and therefore result in more carbon-rich permafrost as well as higher carbon amounts in the active layer. We further hypothesize that the expansion of free roaming large Arctic mammals might be a possibility to stabilize permafrost ground conditions in thaw-affected Arctic steppe and tundra regions.