Linking tundra vegetation, snow, soil temperature, and permafrost

Abstract

Abstract. Connections between vegetation and soil thermal dynamics are critical for estimating the vulnerability of permafrost to thaw with continued climate warming and vegetation changes. The interplay of complex biophysical processes results in a highly heterogeneous soil temperature distribution on small spatial scales. Moreover, the link between topsoil temperature and active layer thickness remains poorly constrained. Sixty-eight temperature loggers were installed at 1–3 cm depth to record the distribution of topsoil temperatures at the Trail Valley Creek study site in the northwestern Canadian Arctic. The measurements were distributed across six different vegetation types characteristic for this landscape. Two years of topsoil temperature data were analysed statistically to identify temporal and spatial characteristics and their relationship to vegetation, snow cover, and active layer thickness. The mean annual topsoil temperature varied between −3.7 and 0.1 ∘C within 0.5 km2. The observed variation can, to a large degree, be explained by variation in snow cover. Differences in snow depth are strongly related with vegetation type and show complex associations with late-summer thaw depth. While cold winter soil temperature is associated with deep active layers in the following summer for lichen and dwarf shrub tundra, we observed the opposite beneath tall shrubs and tussocks. In contrast to winter observations, summer topsoil temperature is similar below all vegetation types with an average summer topsoil temperature difference of less than 1 ∘C. Moreover, there is no significant relationship between summer soil temperature or cumulative positive degree days and active layer thickness. Altogether, our results demonstrate the high spatial variability of topsoil temperature and active layer thickness even within specific vegetation types. Given that vegetation type defines the direction of the relationship between topsoil temperature and active layer thickness in winter and summer, estimates of permafrost vulnerability based on remote sensing or model results will need to incorporate complex local feedback mechanisms of vegetation change and permafrost thaw.

Microclimatic comparison of lichen heaths and shrubs: shrubification generates atmospheric heating but subsurface cooling during the growing season

“…The dry and warm field season of 2018 might have amplified the difference in microclimatic conditions between lichens and shrubs. However, several studies across the Arctic or studies conducted in boreal forests reported similar results as in our study concerning the difference in microclimatic conditions between lichens and shrubs (Loranty et al, 2018b;Mikola et al, 2018;Grünberg et al, 2020). Moreover, the expansion of shrubs in general is associated with higher summer soil temperatures and atmospheric heating (Myers-Smith et al, 2011).…”

“…Shrubs benefit from recent climate change, since the higher temperatures and longer growing seasons are in favor of their growing conditions (Myers-Smith et al, 2011, 2020. Indeed, many studies found an increase in shrub cover, biomass, and abundance in alpine and Arctic areas over the past decades (Sturm et al, 2001b;Hallinger et al, 2010;see Myers-Smith et al, 2011, for a review). Such an increase in shrubs alters the vegetation composition in these areas (Pajunen et al, 2011;Boscutti et al, 2018).…”

Summary and synthesis of Changing Cold Regions Network (CCRN) research in the interior of western Canada – Part 2: Future change in cryosphere, vegetation, and hydrology

“…3.5). Shrub expansion can have multi-directional hydrological impacts (Grünberg et al, 2020), including shrub-snow interactions (Sect. 3.2) and increasing ET (Sect.…”

Standardized monitoring of permafrost thaw: a user-friendly, multiparameter protocol

“…Background Snow cover exerts a fundamental control on the thermal and hydrological regime of permafrost. It acts as an insulator thanks to its low thermal conductivity, reducing heat loss in winter (Zhang, 2005;Grünberg et al, 2020). The type of vegetation cover can significantly influence the insulating power of snow as plants affect the distribution of snow and its depth (Domine et al, 2018).…”

“…However, two additional factors have to be considered when using maximum thaw depth as an indicator of permafrost response to climate conditions. Firstly, the maximum annual thaw depth varies from year to year in response to interrelated variables such as soil moisture, vegetation, and snow (e.g., Walker et al, 2003;Shiklomanov et al, 2010;Grünberg et al, 2020). Secondly, the thawing of icerich permafrost primarily induces subsidence rather than increases in thaw depth (Osterkamp et al, 2009;O'Neill et al 2019).…”