Plant communities and soils in cryoturbated tundra along a bioclimate gradient in the Low Arctic, Alaska

Nonsorted circles and earth hummocks are important landscape components of the arctic tundra. Here we describe the vegetation on these frost-heave features at seven study sites along a N-S-transect from the Arctic Ocean to the Arctic Foothills, Alaska. We established 117 releves in frost-heave features and surrounding tundra and classified the vegetation according to the Braun-Blanquet sorted-table method. We used Detrended Correspondence Analysis to analyze relationships between vegetation and environmental variables. We identified nine communities: Braya purpurascens-Puccinellia angustata community (dry nonsorted circles, subzone C); Dryas integrifolia-Salix arctica community (dry tundra, subzone C); Sal ic i rotundifol iae-Caricetum aquati l is ass. nov. (moist coastal tundra, subzone C); Junco biglumis-Dryadetum integrifol iae ass. nov. (moist nonsorted circles, subzone D); Dryado integrifol iae-Caricetum bigelowii Walker et al. 1994 (moist tundra, subzone D); Scorpidium scorpioides-Carex aquatilis community (wet tundra, subzone D); Cladino-Vaccinietum vit isidaeae ass. nov. (dry nonsorted circles and earth hummocks, subzone E); Sphagno-Eriophoretum vaginati Walker et al. 1994 (moist tundra, subzone E); and Anthelia juratzkanaJuncus biglumis community (wet nonsorted circles, subzone E). The DCA ordination displayed the vegetation types with respect to complex environmental gradients. The first axis of the ordination corresponds to a bioclimate/pH gradient, and the second axis corresponds to a disturbance/soil moisture gradient. Frost-heave features are dominated by lichens, whereas the adjacent tundra supports more dwarf shrubs, graminoids and mosses. Frost-heave features have greater thaw depths, more bare ground, thinner organic horizons and lower soil moisture than the surrounding tundra. The morphology of frost-heave features changes along the climatic gradient, with large, barren nonsorted circles dominating the northern sites and vegetated, less active earth hummocks dotting the southern sites. Thawing of permafrost and a possible shift in plant community composition due to global warming could lead to a decline in frost-heave features and result in the loss of landscape heterogeneity.