Thermo-erosion gullies boost the transition from wet to mesic vegetation

Abstract

Continuous permafrost zones with well-developed polygonal ice-wedge networks are particularly vulnerable to climate change. Thermo-mechanical erosion can initiate the development of gullies that lead to substantial drainage of adjacent wet habitats. How vegetation responds to this particular disturbance is currently unknown but has the po-5 tential to strongly disrupt function and structure of Arctic ecosystems. Focusing on three major gullies of Bylot Island, Nunavut, we aimed at estimating the effects of thermo-erosion processes in shaping plant community changes. Over two years, we explored the influence of environmental factors on plant species richness, abundance and biomass studying 197 polygons that covered the whole transition from intact wet 10 to disturbed and mesic habitats. While gullying decreased soil moisture by 40 % and thaw front depth by 10 cm in breached polygons, we observed a gradual vegetation shift within five to ten years with mesic habitat plant species such as Arctagrostis latifolia and Salix arctica replacing wet habitat dominant Carex aquatilis and Dupontia fisheri. This transition was accompanied by a five time decrease in graminoid above-15 ground biomass in mesic sites. Our results illustrate that wetlands are highly vulnerable to thermo-erosion processes that may rapidly promote the decrease of food availability for herbivores and reduce methane emissions of Arctic ecosystems.Smith, 2011). Abstract IntroductionConclusions References Tables 25 ther et al., 2013) and in the Antarctic Dry Valleys (Levy et al., 2008). On Bylot Island in Nunavut, thermo-mechanical erosion by water has initiated internal tunneling and the development of gully networks in both aeolian and organic depositional environments which cover about 20 000 m 2 (Fortier et al.

Transitions in Arctic ecosystems: Ecological implications of a changing hydrological regime

“…Changes to biogeochemical cycling can occur from changes in hydrology and resulting ecological communities. Striking examples of changes in hydrology in relation to permafrost warming and thawing include shifts from dry and mesic soils and vegetation communities to wetland communities [ Osterkamp et al ., ; Camill , ; Karlsson et al ., ; McClymont et al ., ; Quinton and Baltzer , ; Baltzer et al ., ] and, conversely, from wet ice wedge polygonal tundra to drier, mesic conditions [ Perreault et al ., ]. Such changes in hydrology are associated with fundamental shifts in greenhouse gas emissions related to soil and sediment redox status and vegetation change [ Moore et al ., ; Olefeldt et al ., ; Hodgkins et al ., ].…”

“…A warming climate can cause either increased thermokarst, resulting in lake formation, or increased drainage as the permafrost thaws [ Sannel and Kuhry , ; Karlsson et al ., ; Perreault et al ., ] (see section ). Both processes are currently being observed in the Arctic, with the magnitude of each depending on the geographic location [ Vincent et al ., ].…”

Effects of changing permafrost and snow conditions on tundra wildlife: critical places and times

“…Over a period of 5-10 years after the apparition of such gullies on Bylot Island, Perreault et al (2015) documented a 40% decrease in soil moisture in affected polygons and a shift in vegetation from wet to mesic as graminoids such as Dupontia fisheri, Eriophorum scheuchzeri, and Carex aquatilis were replaced by Arctagrostis latifolia and Salix arctica. This resulted in a fivefold decrease in the aboveground biomass of grasses and sedges that are the preferred foraging plants of snow geese (Chen caerulescens) in the area.…”

Nonlinear thermal and moisture response of ice-wedge polygons to permafrost disturbance increases heterogeneity of high Arctic wetland

“…Disturbances in polygon fields, such as by thermo-erosion gullying of ice wedges, can occur very rapidly, with severe and immediate impacts on the terrain hydrology and ecological integrity (Fortier et al, 2007). On Bylot Island, one single gully eroded hundreds of polygon ridges over a period of 14 years and clear changes were observed in polygon moisture and vegetation conditions (Godin et al, 2014;Perreault, 2012;Perreault et al, 2015). Changes in cover and surface aspects are obvious near the gullied area and vary between eroded and intact polygons.…”

“…Changes in cover and surface aspects are obvious near the gullied area and vary between eroded and intact polygons. Physical differences, between a closed-rim polygon (intact) and an open one (due to gullying) located only a few meters away, can induce very different plant communities in their respective center in response to changing moisture and active layer conditions (Perreault et al, 2015). Vegetation changes in wetlands have direct implications on the food web; for instance, in the Baffin area (and on Bylot Island), large avian herbivore populations rely on graminoids for support and the most adequate land unit (i.e., wetland) for this type of vegetation is restricted (Gauthier et al, 1996).…”