In recent decades, shrub expansion has been observed in many places over the Arctic in response to climate warming. In 2007 we started research at a pristine Northeast-Siberian tundra site to investigate the relationship between shrub cover and summer thawing of permafrost by experimentally removing the shrub part of the vegetation. This Betula nana removal experiment is still running. The removal plots changed dramatically after three to five years, illustrating the importance of running field experiments longer than the 3-year timescale of a PhD project. The treatment effects became stronger over time as a result of feedbacks between vegetation, permafrost thaw, water and snow, which turned the originally elevated shrub patches into waterlogged depressions and ponds (Nauta et al. 2015). Nine years of measurements in the unchanged control plots showed that the thawing depth was not largest in the warmest summer, as one may expect, but in the wettest summer, implying an important role for precipitation in this ecosystem. We think the exceptional wet summer of 2011 was a trigger for local permafrost collapse outside the experiment, which is confirmed by some preliminary results. The increased thawing induced melting of ice in the permafrost leading to soil subsidence and ponding of water. The resulting thaw ponds show drowning of the shrubs and high methane emission. If a future warmer and wetter climate can more frequently trigger such local permafrost collapse, methane-emitting wetlands would expand in the Siberian lowland tundra landscape, which contrasts with the widely assumed shrub expansion.
|Publication status||Published - Feb 2016|
|Event||Netherlands Annual Ecology Meeting (NAEM) 2016 - Conference Centre "De Werelt", Lunteren, Netherlands|
Duration: 9 Feb 2016 → 10 Feb 2016
|Conference||Netherlands Annual Ecology Meeting (NAEM) 2016|
|Period||9/02/16 → 10/02/16|