Impacts of grazing and climate warming on C pools and decomposition rates in Arctic environments

Arctic ecosystems are important habitats for Arctic breeding geese which in their turn have a profound impact on the vegetation in these areas. The herbivore pressure is currently on the rise in the region and may interact with climate change to drive changes in both productivity and decomposition rates. In this study, we aim to determine the combined impact of warming and geese on C pools and decomposition in two high Arctic habitats, mesic heath and wet meadow. We employed field-experimental warming and grazing treatments in a fully factorial design and quantified their impact on ecosystems C pools and turnover. High grazing levels reduced vascular biomass and litter C pools at both sites, whereas warming reduced moss biomass at the mesic site only. Grazing increased decomposition rates and reduced the amount of labile C in the soil at the mesic site, whereas warming substantially reduced C concentrations by approximately 25%. Intermediate level of grazing had an opposite effect and resulted in increased soil C storage at the mesic site. In contrast, no effects of the treatment on belowground C cycling were found at the wet site. In conclusion, the two levels of grazing and warming impacted on different aspects of the C cycle investigated in this study. The high grazing and warming treatment promoted reduced carbon storage/decomposition both above- and belowground with the strongest effects seen at the mesic site.