INFLUENCE OF REINDEER ON METHANE FLUXES IN ARCTIC TUNDRA ECOSYSTEMS

Abstract

Atmospheric methane (CH4) contributes to global warming and Arctic amplification. CH4 fluxes are important in the Arctic, since approximately 50 % of the global soil organic carbon is stored in the Arctic. Soil moisture and soil temperature are key factors for CH4 fluxes as they regulate microbial activity and redox state, while other factors such as plant functional types and isotopic signature (e.g. δ13C) are also important. Large mammalian herbivores, mostly reindeer in the Swedish Arctic, can change vegetation communities, soil microclimate and soil physico-chemical properties due to trampling, nutrient input and grazing/browsing. This thesis aims to determine the difference in net CH4 fluxes of wet and dry Oro-arctic vegetation between reindeer herbivory excluded areas and ambient areas. Two sites, a wet grass meadow and a dry shrub heath, near Ritsem, Sweden, were investigated. CH4 fluxes were measured six times during the snow free season at reindeer herbivory excluded and ambient areas at both sites. It was measured over two focal shrubs: deciduous shrubs (Betula nana) and evergreen shrubs (Empetrum nigrum). The results showed an overall uptake of CH4 at both the grass meadow and the shrub heath. At the grass meadow this could be due to high quality carbon, while the shrub heath acts like a typical upland habitat. The grass meadow showed no impact of reindeer herbivory on the CH4 fluxes or soil moisture. Variations in the fluxes at the grass meadow were instead affected by soil moisture, soil temperature, surface temperature, δ13C and seasonality. At the shrub heath, reindeer exclusion had an impact on the CH4 fluxes by increasing the uptake under Betula nana. Soil moisture was also lower at the same plots. There was an increase in Betula nana cover at herbivory excluded areas at both study sites, with the biggest difference being at the shrub heath. These findings point towards increased evapotranspiration that dry the shrub heath soil and consequently increase the CH4 uptake under Betula nana at these herbivory excluded areas. In conclusion, there is a larger reindeer herbivory effect at the dry shrub heath than the wet grass meadow.