Why mountain summits were favoured as reference units

The term summit in the context of GLORIA includes the summit area between the peak down to the nearest 10-m elevation contour line.
There are several reasons to use summit habitats as reference units in a large-scale comparison of climate change effects.

  • Summits are well-defined topographic units which can provide comparable conditions; they comprise habitats in all exposures (north, east, south, west) within a small area.
  • On summits selected, shading effects from neighbouring land features can be avoided and therefore, the climatic conditions are largely defined by the altitude. Any other topographical feature is likely to be much affected by diurnal and seasonal variation in insolation as a result of shading by neighbouring features.
  • The species composition in summit areas is typical for the respective elevation because the flora is not enriched by elements from higher altitudes.
  • Topographic diversity at summits can result in a high variety of niches, causing high species richness. The presence of narrow transition zones between habitats or vegetation types may enable a rapid recognition of climate-induced shifts of boundaries.
  • Conversely, summits may function as traps for upward-migrating cryophilic species with weak competitive abilities. This is particularly critical on isolated mountains with a high percentage of endemic species occurring only at the uppermost elevation levels. Summit areas are not prone to severe disturbance such as debris falls or avalanches. This enhances their value for long-term observations.
  • Summits are prominent landmarks which can be easily relocated.

For these reasons, mountain summits are considered as the most appropriate sites for comparing ecosystems along climatic gradients. For the selection of monitoring sites, however, certain criteria have to be considered to avoid possible disadvantages (for details see the GLORIA Field Manual).

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