Articles | Volume 13, issue 4
Research article
01 Mar 2016
Research article |  | 01 Mar 2016

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

Naïm Perreault, Esther Lévesque, Daniel Fortier, and Laurent J. Lamarque

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 potential to significantly disrupt function and structure of Arctic ecosystems. Focusing on three major gullies of Bylot Island, Nunavut, we estimated the impacts of thermo-erosion processes on plant community changes. We explored over 2 years the influence of environmental factors on plant species richness, abundance and biomass in 62 low-centered wet polygons, 87 low-centered disturbed polygons and 48 mesic environment sites. Gullying decreased soil moisture by 40 % and thaw-front depth by 10 cm in the center of breached polygons within less than 5 years after the inception of ice wedge degradation, entailing a gradual yet marked vegetation shift from wet to mesic plant communities within 5 to 10 years. This transition was accompanied by a five times decrease in graminoid above-ground biomass. Soil moisture and thaw-front depth changed almost immediately following gullying initiation as they were of similar magnitude between older (> 5 years) and recently (< 5 years) disturbed polygons. In contrast, there was a lag-time in vegetation response to the altered physical environment with plant species richness and biomass differing between the two types of disturbed polygons. To date (10 years after disturbance), the stable state of the mesic environment cover has not been fully reached yet. Our results illustrate that wetlands are highly vulnerable to thermo-erosion processes, which drive landscape transformation on a relative short period of time for High Arctic perennial plant communities (5 to 10 years). Such succession towards mesic plant communities can have substantial consequences on the food availability for herbivores and carbon emissions of Arctic ecosystems.

Short summary
We investigated the impacts of climate change and thawing permafrost on vegetation dynamics in Bylot Island, Nunavut. The development of gullies has created new drainage systems within the wetlands, promoting the emergence of mesic plants at the expense of hydrophilic ones within 10 years after disturbance inception. The landscape transformation from wet to mesic plant communities can have substantial consequences on food availability for herbivores and methane emissions of Arctic ecosystems.
Final-revised paper