There are manifold effects of disturbance on alpine vegetation ranging in their effects from the death of individual plants or small patches of vegetation to more severe impacts over large areas.

Infrequent but severe disturbances (such as large landslides and volcanic eruptions) may be catastrophic for the existing vegetation and, if so, will be followed by primary succession.

On many regularly disturbed areas, plant communities have evolved that are adapted to these particular environmental conditions:

Vegetation development in areas exposed to very frequent disturbance such as freeze-thaw and solifluction may be permanently arrested in an early successional state.

Large areas in alpine environments are mosaics of young and old successional stages of revegetation. Species diversity (as well as species richness) usually is highest at intermediate disturbance levels.

In relatively undisturbed areas the vegetation is often composed of very old and slow growing individuals of a few species.
Disturbances locally disrupt the vegetation and create new conditions, which allow additional plant species to establish at least temporarily. The patches of vegetation at different successional stages will harbour different types of plants thus leading to a higher overall diversity.
However, high levels of disturbance allow only a few well adapted species to grow.

4 - Disturbance and species diversity

The intermediate-disturbance hypothesis predicts that the diversity of species in an ecosystem is highest at intermediate levels of disturbance. Because of the high frequency and diversity of disturbance, this hypothesis is of particular importance in alpine environments.

If we compare the response of vegetation in the lowlands and the alpine environment to similar disturbances, we may see differences. These may be related not only to differences in disturbance intensity, but to other interacting factors such as constraints of resource availability on plant growth and the pool of available species that can cope with such disturbances.
For example, mudslides may be rapidly re-colonized at low altitudes due to the presence of a great variety of pioneer plants and less limiting growth conditions. In the alpine environment mudslides may be colonized by only a limited number of species that cannot build up a closed vegetation cover rapidly (which might have repercussions on further disturbance frequency).

29 August 2011
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