Vegetation can strongly regulate permafrost degradation at its southern edge through changing surface freeze-thaw processes

Permafrost contains twice as much carbon as the atmosphere and the degradation of permafrost due to climatic warming, which could potentially change the global carbon cycle and could also enhance global climate change. It is well studied that permafrost degradation could result in vegetation transition. Aboveground vegetation can act as a buffer for climatic warming, however its role in regulating permafrost degradation remains unclear. In this study we examined how different vegetation types regulated the amplitude and duration of diurnal soil freeze/thaw (FT) cycles and the timing of seasonal soil FT. Soil temperature data (hourly and half hourly) was collected from paired forest-steppe sampling plots spanning a large spatial gradient from northern China to southern Siberia, Russia from 2008 to 2015. FT cycles were found to be larger in amplitude and longer in duration in steppe sites in comparison to forest sites. Soils in the forest sites and steppe sites freeze almost simultaneously, but experience a delay in thawing of approximately 14, 19 and 25 days for deciduous broadleaf forest, evergreen coniferous forest, and deciduous coniferous forest, respectively. Variations in snow accumulation due to differences in vegetation structure as opposed to solar radiation were responsible for the disparity in thaw timing. These findings imply that deciduous conifer forest in east Eurasia could reduce carbon emissions more effectively than evergreen conifer forest in west Eurasia by slowing down warming-induced permafrost degradation during spring thaw.