Siliceous, mostly acidic screes, moraines or stone rivers found at high altitudes and cool sites in mountain ranges through the nemoral zone of Europe. The screes are colonised by a range of mostly perennial, mostly acidophilous plants, the composition strongly influenced by altitude and regional climate and often including many relic and local endemic species, though less than on calcareous screes. Often the vegetation cover is sparse but these screes can be more humid because of the impervious and water-retentive character of the substrates and long snow-lie also encourages luxuriant growth and accummulation of humus.