Vegetation and frost activity in an alpine fellfield on the summit of Plateau Mountain, Alberta

An ordination of alpine fellfield vegetation of the Highwood Range of Southwestern Alberta, Canada, revealed that it varies continuously in response to frost activity gradients of two scales: (1) annual or historic congeliturbation which has produced sorted patterned ground structures similar to those found in arctic tundra and some temperate zone alpine tundra regions, and (2) diurnal congeliturbation which produces frost boils within the larger sorted patterned ground structures.Long-term frost activity has produced a gradient of ground covered by rock which is associated with the major separation of stands. Along this gradient, vegetation changes gradually from stands dominated by epipetric lichens such as Alectoria minuscula to a Carex–Cetraria alpine turf.Microenvironments produced by the borders of patterned ground features result in a diurnal frost activity gradient associated with the Y-axis of the ordination. The vegetation responds to this gradient as a successional sequence. This sequence runs from denuded frost boils dominated by terricolous lichen species such as Lepraria neglecta and flowering plants such as Salix nivalis to a closed Carex–Cetraria alpine turf. Since reversion to a frost boil may occur at any point in the sequence, this succession seems to be partially a cyclical phenomenon.The degree of soil profile formation corresponds to the degree of vegetational development. Active frost boils contain shallow lithosols which develop into poorly developed Alpine Turf soils with progressive vegetation stability.