High altitude vegetation

Tenacious, frugal plants

Eritrichium nanum (All.) Schrader | APAM Archive, G. Pallavicini

The environment of rock faces above the tree line is an extreme habitat for plants due to prohibitive climatic conditions and all the difficulties associated with the lack of real soil, such as lack of water and nutrients.

But even the barest rocks are very often only apparently lifeless: a multitude of so-called lower plants (algae, lichens, mosses, etc.) are able to directly colonize even the compact rocky substrate. The activity of all these microscopic plants helps to breakdown the rock surface, and decomposing they deposit small amounts of humus in the cracks. These small pioneers thus create the necessary conditions for the establishment of higher plants, fissure plants with highly developed root systems capable of penetrating for several metres in search of aquifers in the rocks. These plants are subject to considerable ecological contrasts: often without snow cover, they have to suffer the action of wind and polar temperatures. They also have to withstand the extreme overheating of the rock, considerable daytime temperature fluctuations and the high transpiration of the hottest days.

These rupicolous plants sink their roots in direct contact with the rocky substrate, which is another fundamental flora selection factor. From this derives the clear differentiation between the flora of acid substrates, calcifuge plants, and the flora that prefers substrates with a high calcium content, lime lovers.

Among the most characteristic acid loving rupicolous species are: 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 most representative lime lovers we find: Saxifraga caesia, Saxifraga moschata, Saxifraga diapensioides, Arenaria moheringioides, Ptylotrichum halimifolium, Primula allionii, Primula marginata, Vitaliana primulaeflora, Petrocallis pyrenaica, Silene acaulis and Leontopodium alpinum.
Accumulations of debris at the base of overhanging walls, as well as moraines, alluvial cones or even debris cones, constitute one of the most relevant landscape aspects of the Alpine environment, in which the force of gravity makes a clear selection, increasing the granulometry of the debris from top to bottom: larger boulders are located lower down, smaller ones above. In order to colonise these environments, plants must be able to germinate their seeds in the earthy layer at the bottom of the scree; at the same time they must be able to react vigorously to broken roots and stems.

Characterized by greater stability, siliceous scree, the most common in the Park, constitutes a suitable soil for species that generally need less disturbing conditions, such as cushion plants, or for organisms such as mosses and lichens, which grow extremely slowly. The most common species on these very special soils are Adenostyles leucophylla, Viola argenteria, Achillea herba-rotta, Thlaspi limosellaefolium and Hutchinsia alpina.

Although limestone detritus, is not able to guarantee the same levels of stability, it can provide plants with a greater amount of nutrients than similar siliceous substrates, as with the latter less ions are washed away by atmospheric agents and therefore lost to all intents and purposes of plant nutrition. Among the typical species of calcareous scree, well represented in the eastern sector of the Park in relation to its location within the sedimentary cover of the crystalline massif, are: Papaver rhaeticum, Thlaspi rotundifolium, Centranthus angustifolium, Arenaria montana, Galeopsis reuteri, Gypsophila repens, Doronicum grandiflorum and Cerastium alpinum.