Alpandino :: Plants and climatic stress :: Low temperature extremes

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 - Rumex alpinus

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. Frozen leaves look like wilting before they get brown - why? One immediate consequence of damaging low temperatures is the disruption of cell membranes. As they become "leaky" the cell pressure (turgor) collapses and leaves lose shape. Such damage does not become visible in mature evergreen leaves, because their shape is determined by thick cell walls and not by turgor.

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 - Pulsatilla alpina ssp. apiifolia

In late summer, an early frost can prevent the completion of reproduction. These Pulsatilla alpina plants were frozen stiff - not a problem by itself, but a strong wind broke the flower stems. Leaves and belowground plant parts are unaffected. Note, most green leaves are protected by a thin layer of snow. Such late summer damages occur quite regularly. They affect the reproductive cycle and may cause partial leaf losses, but they are not fatal to these long lived plants, who possess large belowground structures. All plants visible on this picture can propagate by clonal growth.

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

3 - Picea abies

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. Old needles and dormant buds remain unaffected. Given that c. 80 % of the photosynthetic machinery is in old leaves, which are resistant to such stress, the loss of one spring flush in one out of several years is not a big problem. Treeline trees are commonly packed with reserves and not short in photosynthates.

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. They represent the most sensitive group with respect to freezing tolerance. Snow protects these plants from critically low temperatures (Soldanella pusilla, Central Alps 2500 m). What looks like extreme stress in fact represents one of the places in the Alpine which is best protected from critically low temperatures. Snow fields in snow accumulation habitats melt very late in spring. Snowbed specialists such as Soldanella species have preformed flowers (made in the previous season) which start to expand, once "warm", zero degree melting water seeps into their rosettes and once solar radiation penetrates the thinned snow pack. The fragile flowers do not push through snow and ice, they "melt through". Their flowers attract long wave radiation which causes snow to melt faster in the immediate neighbourhood of such structures. This assists these plants to make efficient use of the short season at such snowbed habitats.

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). Snow is the key to survival in cold climates. Lacking snow, as here in the subtropical mountains of Argentina, makes this a much more hostile place for plants and animals than one would expect for such low latitudes. 26° S, 4250 m, Argentinean Andes. See also surviving the cold.

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 - Surviving the cold

Plants which cope with cold climates must tolerate deep freezing temperatures. Otherwise they have to "seek" secure places during critical periods: below snow or below ground. Control over their phenology is critical, and includes not getting tricked by short warm spells and becoming active at the wrong time. The thick snow cover in the sub-arctic mountains beyond the polar circle in N-Sweden represents a "warm blanket", often even preventing soils from freezing. Lemmings are most active under this protective shield and die if snow is missing. Photograph: Deep winter in March in the northern Scandes, 800 m, 68° N. See also Morphological or phenological escape.

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