| Summary: | The Arctic’s ecosystems have developed unique adaptational traits allowing it to sustain life despite polar desert conditions including low precipitation, short summer seasons, and low summer temperatures. Nevertheless, climate change threatens to put this pristine northern ecosystem under stress with increasing surface air temperatures and precipitation. All of these changes are causing pivotal strains on the Arctic’s carbon budget which are poorly understood. We might observe greater CO2 uptake due the migration of shrubs within the tundra biome or observe a greater release of CO2 caused by increased decomposition rates from warmer soils. This study addresses knowledge gaps and current ecosystem conditions on western Axel Heiberg Island, to set ecological baselines to understand how the Arctic’s biophysical properties will change under future climate change pressures. First, a new comprehensive botanical survey of vascular plant species was conducted, which showed that the coexistence of younger colonizer plants and late succession species defines western Axel Heiberg Island as a polar desert oasis. Second, a total of five vegetation communities were distinguished based on dominant species, biotic cover, species composition and soil moisture. Amongst them were two barren habitats (xeric dwarf shrub barren and xeric-mesic dwarf shrub barren), one tundra (dwarf shrub tundra), one heath (cassiope heath) and one wetland habitat (sedge meadow). Third, with the help of carbon flux chambers it was demonstrated that during the late summer period of 2021 both tundra and wetland habitats on Axel Heiberg Island were carbon sink environments, while the barren and heath communities were carbon source environments. Fourth, using these results and a landcover classification map produced with imagery from WorldView-3, the 25km2 study area should be defined as a carbon source environment in the summer of 2021. M.Sc.
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