Ground ice melt in the high Arctic leads to greater ecological heterogeneity

Abstract

Summary 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 temperature‐sensitive permafrost. 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. 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. 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 soil chemistry. 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 (β‐diversity) across the landscape. 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.

Maintain Spatial Heterogeneity, Maintain Biodiversity—A Seed Bank Study in a Grazed Alpine Fen Meadow

“…This contribution was characterized by a zonal pattern because distinct species compositions among transects reflected a high turnover rate— many species appeared and many disappeared along the water depth gradient. This gradient in the non‐inundated area can also be referred to as “wet‐to‐dry gradient” as the water depth becomes negative on dry land, such as the high Arctic (Becker et al , ) where the water depth gradient caused by melting ice essentially broadens the limits for biota, promoting the existence of wetland species. This role of the “wet‐to‐dry” gradient is comparable to the Tibetan region, which is known as “the third world pole.” Unlike other experiments in which dominant zonal species are almost exclusively emergent species (Seabloom & Van der Valk, ; Yuan et al , ), the zonal pattern in Gahai Lake is more distinct, ranging from submerged species to obligate/facultative upland species both for the seed bank and vegetation.…”

“…Hydrology shapes spatial heterogeneity (particularly in the form of a soil moisture gradient and variant topographic microhabitats), which enables the coexistence of more species (Becker et al , ; Freestone & Harrison, ). Such mechanisms make wetland the hub of biodiversity (Lougheed et al , ).…”

Impacts of Degrading Ice‐Wedges on Ground Temperatures in a High Arctic Polar Desert System

“…IW thermokarst drives microtopographic changes and succession dependent on the amount of degradation that has occurred. These geomorphic changes of IW troughs create niche environments that impact vegetation (Becker et al, ; Billings & Peterson, ; Jorgenson et al, ), surface hydrology (Woo & Guan, ; Fortier et al, ; Boike, Wille, et al, 2008; Helbig et al, ; Liljedahl et al, ), snow distribution (Gouttevin et al, ), and carbon fluxes (Lara et al, ; Wainwright et al, ).…”

“…Recent studies have focused on summer processes where IW degradation leads to changes in ecosystem function (Becker et al, ; Jorgenson et al, ; Wolter et al, ), increases in microtopography (Jones et al, ), and changes in surface hydrology (Woo & Guan, ; Fortier et al, ; Boike, Wille, et al, 2008; Helbig et al, ; Liljedahl et al, ). Generally, there is a paucity of winter ground temperature monitoring for IWs, and for detailed field monitoring of IW systems in the high Arctic.…”

“…Vegetation is commonly found in IW troughs and shallow depressions and is sustained from moisture generated by spring snow melt and ground ice melt in warmer summers, whereas cooler summers tend to have more rain (Edlund & Garneau, ). Becker et al () showed that degraded IWs led to more diverse plant communities. Previous studies monitoring IW degradation in the area have solely focused on anthropogenic disturbance, at the Gemini E‐10 well site (Couture, ) and at the abandoned Environment Canada runway located 5 km north of the Eureka Weather Station (Figure ; Hodgson & Nixon, ; Couture & Pollard, ; Becker & Pollard, ).…”