Recovery of ecosystem carbon fluxes and storage from herbivory.

The carbon (C) sink strength of arctic tundra is under pressure from increasing populations of arctic breeding geese. In this study we examined how CO ₂ and CH ₄ fluxes, plant biomass and soil C responded to the removal of vertebrate herbivores in a high arctic wet moss meadow that has been intensively used by barnacle geese ( Branta leucopsis ) for ca. 20 years. We used 4 and 9 years old grazing exclosures to investigate the potential for recovery of ecosystem function during the growing season (July 2007). The results show greater above- and below-ground vascular plant biomass within the grazing exclosures with graminoid biomass being most responsive to the removal of herbivory whilst moss biomass remained unchanged. The changes in biomass switched the system from net emission to net uptake of CO ₂ (0.47 and -0.77 μmol m ^-2  s ^-1 in grazed and exclosure plots, respectively) during the growing season and doubled the C storage in live biomass. In contrast, the treatment had no impact on the CH ₄ fluxes, the total litter C pool or the soil C concentration. The rapid recovery of the above ground biomass and CO ₂ fluxes demonstrates the plasticity of this high arctic ecosystem in terms of response to changing herbivore pressure.