346 INTRODUCTION TO PLANT GEOGRAPHY [CHAP. 



and westwards to the Rocky Mountains the local dominants in the 

 northern or ' Hudsonian ' belt are usually one or more of the follow- 

 ing : White Spruce {Picea glauca agg.), Black Spruce (P. mariana), 

 Tamarack (Larix laricina), Balsam Fir (Abies balsamea), Jack Pine 

 (Piniis banksiana), with or without associated broad-leafed Poplars, 

 Birches, or American Aspen {Popuhis tremuloides). Farther south, 

 other dominants enter and in time there is a grading into the 

 deciduous summer forest. Tall shrubs such as Willows {Salix spp.), 

 Scrub-birches, and species of Dogwood {Cornus) and Pimbina etc. 

 (Viburnum) may be plentiful, especially in damp situations where 

 Mosses form a characteristic carpet. Herbs are, however, usually 

 little in evidence, the normal ground-flora being heathy, including 

 various species of Blueberry etc. (Vaccinium spp.), Labrador-tea 

 (Ledum spp.). Pale-laurel (Kalmia spp.), and the Crowberry 

 (Empetrum nigrum s.l.), typically alternating with or growing out of a 

 lichen-rich carpet in the drier situations. In the damper situations 

 the ground layer is contrastingly mossy. Farther west the Balsam 

 Fir and Jack Pine are replaced by other species, particularly by 

 Alpine Fir (Abies lasiocarpa) and Lodgepole Pine (Pinus contorta 

 var. latifolia), while in Eurasia the dominant species are different 

 again. Thus in northern Europe the Scots Pine (Pinus sylvestris) 

 is often the sole dominant in the west, with Norway Spruce (Picea 

 abies) entering to the south and east, and, farther east still, Siberian 

 Spruce (Picea obovata), Siberian Larch (Larix sibirica s.l.), Siberian 

 Fir (Abies sibirica), and, ultimately, Siberian Stone-pine (Pinus 

 sibirica). Except for Norway Spruce these all persist at least well 

 into Siberia proper, or are confined thereto. In the centre and east 

 of Siberia, however, the Siberian Larch is replaced by the Dahurian 

 Larch (Larix dahurica) and the Siberian Stone-pine by the Siberian 

 Dwarf-pine (Pinus pumi la). Apart from this last, which is shrubby, 

 most of these Conifers (including the Lapponian form of Scots 

 Pine) are short-branched, at least above, to give a conical shape. 

 Moreover they tend to be shallow-rooting, and consequently able to 

 grow in open canopy in areas where the subsoil is permanently 

 frozen. Examples are seen in Figs. 97 and 98, the ground-flora 

 almost everywhere being of the characteristic heathy type. 



2. The open park-like ' taiga ' occurring towards the northern 

 limit of arborescent growth. This is really only the product of 

 depauperation of the various faciations of northern coniferous forest 

 just described, but it is so striking in appearance as to warrant 

 separate mention. It is characterized by the rather sparsely and 



