CHAP. Liii BUSH AND FOREST ON ACID HUMUS SOIL 215 



The vegetation on the ground consists of those communities that belong 

 to the formations already described as occurring on sour soil. 



As examples of such hushland composed of true shrubs, we may mention 

 the following : 



i. Arctic Bushland on Acid Soil. 



In the far north, for example on the tundra in Lapland, Betula nana 

 and other kinds of birches occur as low fiat bushes, and are often associated 

 with grey-haired willows, such as Sahx glauca and S. lanata. On 

 Scandinavian mountains immediately above the tree-hmit occurs the 

 zone of grey willows, including Sahx lanata, S. glauca, and others, whose 

 leaves are protected from excessive transpiration by means of a coating 

 of hairs, and also by a thick-walled epidermis, wax, and the like. In 

 Greenland, at 70 N., one finds similar willow-bushlands which are up to 

 one metre in height, with stems and branches interlaced, and are composed 

 of Salix glauca and Betula nana. But these bushlands should perhaps 

 be regarded as mesophilous.^ On Norwegian mountains in hke manner, 

 Betula nana, willows, and juniper form extensive low bushlands which 

 are about ^ | metre in height and correspond most closely to the Rhodo- 

 dendron-bushlands of the Alps. 



ii. Subalpine Bushland on Acid Soil. 



Where, as in Central Europe, the summits of the highest mountains 

 still lie in the cloud-belt, the production of raw humus is promoted 

 by the moist misty air and low temperature, and there arise on acid 

 soil bushlands that cover considerable areas above the limit of forest. 

 Rhododendron-bushland is closely allied to dwarf -shrub heath. It occurs 

 on the Alps and Pyrenees, also, in a taller, more forest-hke form, on the 

 Himalayas. It is produced by species of Rhododendron (sometimes 

 accompanied by Juniperus communis), and the protection against tran- 

 spiration here is provided by scale-like hairs and a coating of resin. On 

 the calcareous Alps Rhododendron hirsutum gives rise to the formation, 

 but in the central Alps it is R. ferrugineum. In Rhododendron-bushland 

 there grow a number of dwarf-shrubs that occur on heaths for example, 

 Vaccinium and Calluna.^ 



Other subalpine associations for instance, in Servia^ are composed 

 of Juniperus communis or species of Vaccinium, or of mixtures of these. 



On high, windy situations on mountains and on windy sites in extreme 

 northern latitudes, there is, just as in high-moor, bushland or stunted 

 forest composed of arboreous species that elsewhere form high-forest. 

 The common spruce (Picea excelsa) in Lapland occurs as a creeping shrub 

 that repeatedly strikes root ; it assumes peculiar, rounded, very compactly 

 branched, low, shrub-hke shapes, and occurs singly or forms extensive carpets 

 of bushland, as its slender branches are partly concealed in the lichen- 

 heath.'* It derives its protection against transpiration from the structure 

 of its leaves. The Scots pine (Pinus sylvestris), and, in Siberia, Pinus 



' See Chap. XCI. 



" For details see Kerner, 1863 ; Hayek, 1907 ; Christ, 1870 ; Schroter, 1904-8. 



* Adamovicz, 1898. * See ilhistrations in Kihlman, 1890. 



