fulltext - DiVA

Plant Cover of the Alpine RegionsBy OLAV GJJEREVOLL and KARL-GO RAN BRINGERSNOW DISTRIBUTIONBy Olav Gj oorevollSrtow is a most. decisive factor for the distributionof the different plant communities in the Il).OUntains(VESTERGREN 1902). The snow is swept awayby the wind, from ridges, crests, and peaks, andis left in depressions and valleys. This uneven distributionof snow is repeated every year. Theamount of snow may vary considerably, but thedistribution is about the same.In the early snow-free areas the plant communitiesconsist of species which are able to stand lowtemperatures and, partly, heavy wind erosion aswell. In summer these areas will be exposed tosevere desiccation. 'J'he predominant species areaccordingly xerophilous, in the low-alpine regiona number of dwarf shrubs, in the middle-alpineregion grasses, sedges and brushes. They form differentchionophobous communities.The snow-drifts, on the other hand, involve agreater or smaller shortening of the vegetativeseason. The snow-bed plants, therefore, are suchspecies as can do with a more or less heavily reducedgrowth period. They form chionophilous communities.They are not exposed to particularly lowtemperatures, because the snow offers an excellentprotection. (E. DAHL 1956).There are usually no sharp-cut borders betweenchionophobous and chionophilous plant communities.Transitional types will always be found.After the snow has melted, moisture conditionsare apt to vary considerably in the snow-bed areas.In the communities on the upper margin of thesnow-drifts the soil will dry up rapidly, whereasthose situated on the lower side of long-lastingsnow-drifts will be irrigated for a shorter or longerperiod. In many snow-bed communities, therefore,the element of hygrophytes is great and this, underalpine conditions with mobile soil water presumablyrich in oxygen, usually leads to formation ofmeadow-like vegetation.The most hygrophytic communities, those ofthe alpine springs and mires, are dealt with in anessay by A. PERSSON and are therefore left outhere.The border between the low-alpine and themiddle-alpine regions is not evident in the snowbeds,for the composition of the low-alpine andmiddle-alpine snow-bed communities is fairly similar,a condition not found in the correspondingheath communities, where the presence of Vacciniummyrtillus heath in the low-alpine belt makes a greatdifference. The time of exposure may occur evenas late in a low-a1pine snow-bed as in a middlealpineone. The areal extension of chionophilousplant communities is however much larger · in themiddle-alpine region.CHIONOPHOBOUS PLANT COMMUNITIESBy Karl-Goran Bringeris dominated by different dwarf shrubs, while grass­heath communities are of rather small importance.In localities with little or moderate protection bysnow in the low-alpine belt the heath vegetationActa Phytogeogr. Suec. 50