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The term stress originates from physics, where a certain external force exerts a strain on some materials, which may either resist or break under the internal stress imposed by the strain. In biology stress refers to consequences of destructive physical or chemical conditions. Moderate deviations from optimal growth conditions are NOT seen as stress, but as essential "excursions" which have a "training effect" and add to the long-term fitness of an organism. Furthermore, disturbances such as grazing or predation, erosion or burial, fire or wind break are not commonly subsumed under the term stress.
- Stress represents conditions of severe (!) deviation from physiological optimality, which cause a substantial restriction of growth and survival.
- Stress factors operate gradually, but become critical beyond a certain threshold.
- Typical stress factors are excessive low and high temperatures, drought or annoxia, excessive radiation and concentrations of certain chemicals (salts, heavy metals etc.).
In the alpine life zone three types of stress are common and will be discussed here:
- high radiation (including aspects of UV radiation)
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