Influence of Frost Heaving on Soil Chemistry and on the Distribution of Plant Growth Forms

Abstract

This study indicates that vegetation on frost heaved soils is controlled by two main factors: (1) disruptive effects on the belowground parts of the plants when the soil heaves; (2) an increase of nutrient availability, pH, and base saturation following this disturbance. The vegetation changes from a dominance of rhizomatous (mostly graminoids) and woody plants (shrubs and dwarf shrubs) on stable soils, via dominance of dwarf shrubs alone on soils of low disturbance, to dominance of fibrous rooted perennials at the strongest disturbance. I suggest that rhizomatous plants are adapted to grow at sites with a continuous humus cover where they easily can penetrate and exploit the organic matter. They are excluded, however, from frost heaved ground because no continuous humus layer is formed, due to the disturbance. Woody plants are favoured by lack of competition from rhizomatous perennials on soils of low disturbance but they are not able to withstand the disruptive forces of strong frost heaving. The fibrous-rooted plants are not severely damaged even by intense frost heaving since their belowground systems die to a great extent before the onset of freeze-thaw cycles in late autumn. Instead they are problably favoured by the disturbance because competition is reduced, and because they are adapted to high nutrient availability as evidenced by the short lifespan of their root system.