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Forschungsanstalt WSL

Swiss Federal Research Institute WSL
Mountain Ecosystems
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Article

Author(s): WSL-Institute for Snow and Avalanche Research (SLF), Editorial office waldwisen.net - WSL
Editorial office: WSL, Switzerland
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Avalanches Create New Habitats for Plants and Animals

Avalanches not only destroy habitats, but they can also create new ones. A study shows that the biodiversity within avalanche tracks is highly increased compared to the surrounding forest. The more avalanches occur, the more significant the difference becomes.

Lawinenabgang
Fig. 1 - An avalanche rushes down a mountain forest.
Photo: SLF

It’s winter. After strong snow fall, avalanches are rumbling towards the valley. With their enormous power they break trees as if they were wooden match sticks; whatever is in their way is torn down. A few months later, the last snow patches are melting and flowers and grasses are flowering in the avalanche track. The question remains: How do avalanches affect nature?

A study with the WSL-Institute for Snow and Avalanche Research SLF, Davos demonstrates that the destructiveness of avalanches also has positive aspects for nature. It creates environmental conditions which enable an entire range of plant species to survive. Large, dominant trees are cracked by avalanches.

Small-scale change of the environmental conditions

As a consequence, much more light hits the soil compared to the neighboring forest and more water and nutrients are available. And the mechanic stress on small plants due to the avalanche is minor: the snow cove protects them or they are still flexible enough to bend down due to the snow weight.

In a small area there are the most diverse environmental conditions, as the mechanic stress is greatest in the track center since smaller avalanches don’t cover the entire track, and as at some spots snow is ripped away whereas at other spots snow is deposited. Accordingly, the biological diversity is high. Many different plant species and communities find suitable conditions; the "typical avalanche plant species" does not exist. Thus, over 80% of the 141 observed species grew in less than 5% of the investigated plots, although the undisturbed vegetation outside of the avalanche tracks consisted of a larch-spruce forest throughout the entire monitoring area (Dischmatal near Davos GR).

     
Lawinenzug im Berner Oberland Lawinenzug im Kanton Glarus  
Fig. 2 - Avalanche track in the Bernese Alps.
Click to enlarge.
Fig. 3 - Avalanche track in the canton of Glarus.
Click to enlarge.
 
Photos: Thomas Reich (WSL)
   

Three times more species than in the neighboring forest

Waldeidechse
Fig. 4 - Not only plants benefit from the increased supply of light and heat, but also numerous animals such as butterflies or reptiles.
Photo: Thomas Reich (WSL)

In comparison to earlier studies, the SLF study investigates many tracks with differing frequency of comedowns. The more frequent avalanches come down in a track, the richer and more diverse is the vegetation. Avalanche tracks with a comedown every year host approximately three times more species than in the neighboring forest.

Surprisingly, not only pioneer plants take advantage. They are only represented strongly if during the last years the forest was destroyed. Competitive and perennial species prefer the other avalanche tracks. This shows that despite frequent disturbances relatively stable conditions establish.

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