Alpine Regions.—The humus-forming power of the plant covering increases quite rapidly with decreasing temperature and increasing humidity. At alpine altitudes accumulation exceeds decay. Although we do not know the chemical composition of the decaying plant materials, we know that they are rich in organic acids and usually give an acid reaction. On calcareous substrata wind-blown dust and residual soil suffice at first to neutralize the acids. The result is a mild humus of deep-black color, of soft, sticky, and somewhat greasy consistency, with basic or neutral reaction. The Carex firma association or C. mucronata or Sesleria coerulea turf takes possession of such  calcareous soils rich in humus. It withstands the wear of much rain and snow water. The abundant carbon dioxide of the adsorptively saturated humus leads to the formation of bicarbonates. Calcium and magnesium go into solution and are the more completely leached out as the humus is increased by additions of acid-forming litter from such tufted plants as Elyna myosuroides and Agrostis alpina. There results a deep, highly acid rendzina soil (pH 6.5 to 5.5). (Braun-Blanquet 1932:311-2)
BRAUN-BLANQUET, Josias. 1932. Plant sociology: the study of plant communities. (Trans.: George D. Fuller; Henry S. Conard) New York: McGraw-Hill Book Company.