| Summary: | Climate change has affected ecosystem structure and composition in the Arctic during the last few decades. Researchers have observed a greening trend as the active layer depth is increasing due to rising air- and soil temperatures. Align with climatologic factors, Arctic ecosystems have a long history of grazing by large mammalian herbivores and geese. The Grazing Optimization Hypothesis suggests that productivity of an ecosystem should increase if it is exposed to a moderate level of grazing. Even though changes in plant species composition due to these biotic and abiotic controlling factors are to some degree well known, the responses on CO2 fluxes and the carbon cycle are largely unknown. In this paper, studies made on warming and grazing in the Arctic are compiled and analyzed both individually and in a comparing context, to highlight how these factors affect the carbon cycle. Special emphasis has been put on a careful study and evaluation of the few existing experiments which combine treatments of simulated grazing and warming. A case study was performed on primary data from clipped plots in Zackenberg, North-east Greenland. Results show that herbivory seem to be more important in the harsh environments of the Arctic than in more nutritious ecosystems, and a greater grazing pressure is needed for the Grazing Optimization Hypothesis to be true. Depending on grazing pressure, herbivory seem to mitigate the greening effect that climate warming has on the Arctic by preventing dwarf shrubs from invading the tundra. However, since the herbivore’s survival is dependent on the climate in terms of the necessity to get hold of nutritious forage in early spring, climate change will still probably be the most impending factor controlling the Arctic C cycle in the future. Populärvetenskaplig ammanfattning Den Arktiska tundran har påverkats mycket av klimatförändringarna de senaste årtiondena. Den pågående uppvärmningen gör att djupet på det aktiva lagret ökar och att buskiga växter, som annars inte trivs i den kalla ...
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