Permafrost Terrain Stability and Thermokarst Monitoring: - Arctic LCC

8. Benninghoff, W.S., 1952, Interaction of vegetation and soil frost phenomena: Arctic,
v. 5, no. 1, p. 34–44.
This paper describes the influence of frozen soils on the establishment and propagation of
vegetation communities, and the converse of this. Frozen soils exert great force and trauma
on root systems of plants through repeated freeze-thaw cycles, differential frost heaving,
cracks caused by rapid freezing, and so on. Plants have adapted shallow root systems to
adapt to impervious permafrost, which make trees and shrubs easy to overturn in inclement
weather or wind storms. Insufficient depth for the proper functioning of roots limits spruce
forest, and species with flexibility of their root habits are most likely to establish themselves
in permafrost areas. Furthermore, plants may be subjected to severe water loss by exposure
to drying winds while roots are encased in frozen soil and cannot absorb water, which may
also be a contributing factor that limits tree growth in permafrost terrain. Thermokarst
features caused by the melting of variable amounts of ice in the soil change the physical
environment for vegetation occupying a site. Margins of lakes with high permafrost tables
are particularly susceptible to destruction, In the Nebesna, Chisana, and Tanana River
valleys of eastern Alaska, previous research estimated mean shore retreat of 2.3–7.5 in./yr.
The oriented lakes of the Arctic Coastal Plain were shown as constantly changing, owing to
caving of shores, draining, filling with peat, and initiation of new thaw cycles. All
permafrost areas are characterized by the instability of the surface and consequent transience
of site conditions. Vegetation also influences frozen soils. It shields the soil from maximum
penetration of heat through shading, decreases air circulation, retains moisture in and just
above the soil, prevents thaw through root systems, intercepts rain, and cools the soil
through evaporation of moisture on plant surfaces. Mosses may play an important part in
this effect. Removal of moss, thick turf, and surface peat greatly hastens thawing of frozen
ground. However, vegetation also can warm soils by impeding heat radiation from the soil to
the cold air and retaining snow cover, which insulates the ground from lower temperatures.
Vegetation may be important for reducing frost disturbance in tundra through anchoring
roots to the soil and the insulating effects of the aboveground plant parts. Because of soil
frost changes following disturbance, the affected surface and the local environment may
change so much that entirely different communities occupy the site for unknown time
periods.
9. Billings, W.D., and Peterson, K.M., 1980, Vegetational change and ice-wedge polygons
through the thaw-lake cycle in arctic Alaska: Arctic and Alpine Research, p. 413–432.
This paper provides an overview of the thermokarst lake cycle through the study of
vegetation succession in a chronosequence of drained thermokarst lake basins near Barrow,
Alaska. Pioneer species in recently drained lake basins consisted of Dupontia fischerii and
Arctophila fulva. As time passes since drainage, Carex aquatilis becomes more abundant as
does the development of ice-wedge polygonal networks.
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