The altitudinal distribution of taxa reflects their tolerance to low temperature extremes. Alpine plant taxa will not be killed by freezing temperatures, but may suffer partial tissue losses at times.

1 - A clear night (-6 °C) after a storm was too much for these Rumex alpinus leaves at 2500 m in the Swiss Alps in mid summer.

2 - In late summer, an early frost can prevent the completion of reproduction. While frozen, these flowers were broken by wind.

3 - A very late freezing event in spring (June) killed the fragile current year (new) shoots of Picea abies near the treeline in Tyrol at 1960 m elevation.

Mechanisms of freezing resistance in plants

Plants may escape exposure to critically low temperatures by selecting certain habitats, using certain phenology or by specific morphology.

• Escape by habitat selection

  Plants which cannot tolerate freezing are forced into habitats with secure winter snow cover (typical snow bed plants).

• Escape by phenology

  The withdrawal of sensitive tissue from exposed positions during critical periods, is another form of escape. In its extreme form, it is the survival as seed as in the annual life form. Annual plants are very rare in temperate zone mountains, but are regularly found in mediterranean and subtropical mountains.

• Escape by specific morphology

  Plants can position their sensitive meristems below ground permanently (see illustration on the right).

4 - Most herbaceous plants of high altitudes position apical meristems 1 - 3 cm below the ground surface, protecting those critical tissues from radiation frost (here as an example a Perezia species from 4200 m elevation in the Argentinean Andes).

Snow helps in surviving the cold

5 - Habitat selection
Snowbed plants are restricted to places of guaranteed and long-lasting snow cover.

6 - Morphological or phenological escape
A cold winter without snow forces plants to position perennial structures below ground surface and withdraw sensitive parts in time (phenology). 4250 m, Argentinean Andes.

7 - Hiding under snow
A continuous deep winter snow cover envelopes plants in a mild microclimate (800 m, N-Sweden).

29 August 2011
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