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The mountain regions of Lappland 71Fig. 5. The twisted stems of thesubalpine birchwood are lichenfree below the maximum snowlevel, here at about 1-1.5 m.V accinium myrtillus and Deschampsiaflexuosa in the fieldlayer. Near Vietasjokk, Lule Lappmark.Aug. 15, 1959. Photo BjornAllard.(Torne Lappmark) are at 750 m (in the extremenorth at 600 m), and in southern Lappland (Lycksele Lappmark, near Tarna) at 850 m. The decliningfrom east to west of the birchwood limit is considerably less than the corresponding sinking of theupper limit of conifer forest. In the eastern part ofTarna and Sorsele parishes (Lat. N 66°) the birchwood limit is usually at about 800 m. Near theNorwegian border about 70 km farther west thecorresponding limit is at about 700 m. In this partof Lappland the altitudinal width of the subalpinebelt varies from about 100 m in the east to about200 m in the west.The dominant tree of the subalpine belt is themountain birch, Betula pubescens ssp. tortuosa.This is a variable subspecies closely related to thecommon birch of the adjacent conifer belt, Betulapubescens. In fact, the two converge in the lowerparts of the mountain area where intermediatetypes prevail. In an exposed position and on dryinfertile soils the mountain birch is usually polycormic and seldom higher than a few metres. Thebasal parts of the polycormic birches are crookedand twisted owing to snowpressure, snow-creepand wind. In a sheltered position and on fertilesoil the mountain birch often grows with a singlestraight trunk and may be at least 10-12 m high.One of its characteristics is the short, stiff, neverhanging branches with the majority of the leavesin clusters on short shoots.Next to the dominant birch the subalpine woodsalso hold other foliiferous trees. With the exceptionof Betula verrucosa all the common foliiferous treesof North Sweden reach the subalpine belt. Here theyare represented by su balpine or northern racessometimes taxonomically ditinguished, viz. Salixcaprea var. coaetanea, Prunus padus var. borealis,Alnus incana var. virescens, Sorbus aucuparia var.glabrata. Of these Salix caprea var. coaetanea israther abundant on steep, southerfacing ,slopeswith fertile soil. Growing just as high as the mountainbirch, its grayish foliage stands out clearlyagainst the bright green canopy of the subalpinewood. Prunus padus var. borealis, Alnus incanavar. virescens and Sorbus aucuparia var. glabrataoccur only as bushes growing on the rich slopes orActa Phytogeogr. Suec. 50