|1. The polar desert biome of the Canadian high Arctic Archipelago is currently experiencing some of the greatest
mean annual air temperature increases on the planet, threatening the stability of ecosystems residing above
2. Ice wedges are the most widespread form of ground ice, occurring in up to 25% of the world’s terrestrial
near-surface, and their melting (thermokarst) may catalyse a suite of biotic and ecological changes, facilitating
major ecosystem shifts.
3. These unknown ecosystem shifts raise serious questions as to how permafrost stability, vegetation diversity
and edaphic conditions will change with a warming high Arctic. Ecosystem and thermokarst processes tend to
be examined independently, limiting our understanding of a coupled system whereby the effect of climate
change on one will affect the outcome of the other.
4. Using in-depth, comprehensive field observations and a space-for-time approach, we investigate the highly
structured landscape that has emerged due to the thermokarst-induced partitioning of microhabitats. We examine
differences in vegetation diversity, community composition and soil conditions on the Fosheim Peninsula, Ellesmere
Island, Nunavut. We hypothesize that (i) greater ice wedge subsidence results in increased vegetation
cover due to elevated soil moisture, thereby decreasing the seasonal depth of thaw and restricting groundwater
outflow; (ii) thermokarst processes result in altered vegetation richness, turnover and dispersion, with greater
microhabitat diversity at the landscape scale; and (iii) shifts in hydrology and plant community structure alter
5. We found that the disturbance caused by melting ice wedges catalysed a suite of environmental and biotic
effects: topographical changes, a new hydrological balance, significant species richness and turnover changes,
and distinct soil chemistries. Thermokarst areas favour a subset of species unique from the polar desert and are
characterized by greater species turnover (b-diversity) across the landscape.
6. Synthesis. Our findings suggest that projected increases of thermokarst in the polar desert will lead to the
increased partitioning of microhabitats, creating a more heterogeneous high arctic landscape through diverging
vegetation communities and edaphic conditions, resulting in a wetland-like biome in the high Arctic that could
replace much of the ice-rich polar desert.|