Thaw pond development and initial vegetation succession in experimental plots at a Siberian lowland tundra site

Background and aims: Permafrost degradation has the potential to change the Arctic tundra landscape. We observed rapid local thawing of ice-rich permafrost resulting in thaw pond formation, which was triggered by removal of the shrub cover in a field experiment. This study aimed to examine the rate of permafrost thaw and the initial vegetation succession after the permafrost collapse. Methods: In the experiment, we measured changes in soil thaw depth, plant species cover and soil subsidence over nine years (2007–2015). Results: After abrupt initial thaw, soil subsidence in the removal plots continued indicating further thawing of permafrost albeit at a much slower pace: 1 cm y⁻¹ over 2012–2015 vs. 5 cm y⁻¹ over 2007–2012. Grass cover strongly increased after the initial shrub removal, but later declined with ponding of water in the subsiding removal plots. Sedges established and expanded in the wetter removal plots. Thereby, the removal plots have become increasingly similar to nearby ‘natural’ thaw ponds. Conclusions: The nine years of field observations in a unique shrub removal experiment at a Siberian tundra site document possible trajectories of small-scale permafrost collapse and the initial stage of vegetation recovery, which is essential knowledge for assessing future tundra landscape changes.