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Resistant, frugal plants

High altitude vegetation in the Park

Rock faces above the tree line form an extreme habitat for plants because of the prohibitive climatic conditions and all the difficulties connected with the lack of proper soil, such as lack of water and nutrients. However, even the barest rocks are only seemingly lifeless, a multitude of lower plants (algae, lichens, mosses, etc) can directly colonize even solid rock. The action of all these microscopic lower plants contributes to degrade the surface of the rock. The plants also deposit albeit small amounts of humus in crevices in the rock when they decompose. This creates the conditions for rock plants to establish, these have very extensive root systems which can penetrate for several metres to find sources of water in the rocks. These plants are subject to considerable ecological contrasts: often they are free of snow in winter and are subjected to wind and polar temperatures. Then they have to bear the rocks overheating and extreme fluctuations between day and night, and extreme transpiration on hot days.

Rock plants force their roots down in direct contact with the rock surface, which is another factor selecting the flora. In fact there is a distinct difference between acid loving plants that live on acidic substrates and lime loving plants that live on limestone. Among the more characteristic acid lovers we have: Saxifraga florulenta, Saxifraga cotyledon, Eritrichium nanum, Androsace vandelli, Silene acaulis subsp. excapa, Artemisia petrosa, Achillea nana, Saxifraga exarata, Ligusticum mutellinoides, Minuartia sedoides and Minuartia recurva.
Among the more representative lime lovers we should mention: Saxifraga caesia, Saxifraga moschata, Saxifraga diapensioides, Arenaria moheringioides, Ptylotrichum halimifolium, Primula allionii, Primula marginata, Vitaliana primulaeflora, Petrocallis pyrenaica, Silene acaulis and Leontopodium alpinum.

The talus at the base of rock faces, moraine, alluvial cones and scree all form a predominant feature in Alpine scenery. Gravity acts a natural selection, sorting debris with the larger stones at the base and the smaller at the top. To colonize this environment plants have to be able to germinate their seeds in the soil substrate below the scree, at the same time they have to be able to react vigorously to damage to their roots or the exposed part of the plant. Siliceous talus is generally more stable and is the commonest sort found in the Park. It offers a suitable growing medium for species that generally prefer not to be disturbed, like pulvinate plants, or organisms like mosses and lichens, that grow extremely slowly. The commonest species in this rather particular soil are Adenostyles leucophylla, Viola argenteria, Achillea herba-rotta, Thlaspi limosellaefolium e Hutchinsia alpina.
For their part limestone scree slopes, although they don't offer the same stability, can offer plants more nutrients compared with similar siliceous substrates, as with calcareous scree less ions are washed away by precipitation and lost as potential food for plants. Typical species found on calcareous scree found beneath the sedimentary rocks in the eastern part of the Park are: Papaver rhaeticum, Thlaspi rotundifolium, Centranthus angustifolium, Arenaria montana, Galeopsis reuteri, Gypsophila repens, Doronicum grandiflorum e Cerastium alpinum.

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