Vegetational Change and Ice-Wedge Polygons through the Thaw-Lake Cycle in Arctic Alaska

Abstract

Britton's thaw-lake cycle hypothesis is examined and modified in light of new observations on ice-wedges and revegetation following drainage of lakes in the wet coastal tundra of arctic Alaska. Two thaw-lakes which were artificially drained in 1950 provided base-line data for the ages of basin surfaces. Sizes of clonal colonies of Eriophorum angustifolium and Carex aquatilis were used in an attempt to age older, naturally drained lake basins. The floristic composition of the vegetation through the cycle is predictable. Pioneer species are Dupontia fisheri and Arctophila fulva. Eriophorum angustifolium is characteristic throughout all of the terrestrial part of the cycle. Carex aquatilis enters the vegetation slowly but is the most successful competitor and dominates the vegetation for perhaps 2000 to 3000 yr. It disappears locally when thaw-ponds developing from low-center polygons become too deep. Ice-wedges exist longer than the thaw-lakes and persist beneath them. They reassert themselves after drainage and are important in reinitiating the polygonal, terrestrial part of the cycle. Drained lake basins are very susceptible to thermokarst erosion when vehicles damage the insulating peat which covers the ice-wedges. Vegetational succession through the thaw-lake cycle is closely attuned to geomorphic changes and therefore is cyclic. It does not fit most recent models of succession because it is not autogenic but, rather, is controlled by the cold physical environment both above and below ground.