AMPHI-ATLANTIC ZONATION, NEMORAL TO ARCTIC 115 



approach and the terms of these authors differ widely but nevertheless there 

 is a fairly close similarity in the resuhs arrived at, as far as strictly zonal 

 divisions are considered. Space does not allow a discussion, but references 

 may be given to Hare (1959, p. 34). Three sub-zones are more or less generally 

 accepted, but the first of these is further sub-divided in the present paper. 



(a) The southern Boreal sub-zone. Here several of the species mentioned for 

 the Nemoral and Boreo-nemoral zones occur, usually in low frequency: 

 Pinus strobus, P. resinosa, Acer saccharum, Betula lutea, Fraxinus nigra, 

 Uhnus americana, etc. The dominant conifers are Picea mariana, P. glauca, 

 and Abies balsamea, with Pinus Banksiana on rocks and sandy soils and on 

 disturbed sites; birch and particularly aspen are prominent in secondary 

 growth. The sub-zone is typically developed east of Lake Superior. North and 

 northwest of the latter it is virtually absent, only Pinus strobus, P. resinosa, Pop- 

 uhis grandidentata, Uhnus americana, and Fraxinus nigra sparsely representing 

 the southern tree species here. In Manitoba the sub-zone reoccurs, although 

 the southern species are largely different: Acer negundo, Quercus macrocarpa, 

 Uhnus americana, and Fraxinus pennsylvanica var. subintegerrima. This 

 sub-zone is again lacking in Alberta and most of Saskatchewan. 



(b) The Main Boreal sub-zone. As the preceding sub-zone, the Main 

 Boreal is characterized by closed-canopy coniferous forests except on burned 

 sites and bogs and fens. The Boreal conifer species are the same. Abies 

 balsamea is an important forest tree mainly in the east. There is often a com- 

 plete dominance of the two spruces, with Picea mariana on poor soils and 

 P. glauca on the better soils which are more widespread on the sedimentary 

 rocks of the western interior. In some areas Pinus banksiana prevails, and in 

 the westernmost parts Pinus contorta var. latifolia is abundant. The southern 

 species are lacking or represented by very few outposts, mainly of Fraxinus 

 nigra and Uhnus americana; only Thuja occidentalis and Acer spicatum are 

 still fairly common in some parts. Conditions for forest growth are quite 

 satisfactory within this sub-zone which extends across Canada from New- 

 foundland to the upper Mackenzie and the Liard valleys, and possibly even to 

 some of the deep valleys in the mountainous Yukon Territory. 



(c) The Sub-Arctic sub-zone. This is characterized by open, parklike stands 

 usually formed by low black spruce {Picea mariana) with a Cladonia under- 

 growth. These stands are regarded as woodland, but not as true (commercially 

 valuable) forests, although pulpwood size is usually reached. On more 

 favourable sites white spruce {P. glauca) is found, and the undergrowth is 

 often richer in species. Boggy sites are extremely common, both wooded 

 ("black spruce muskegs") and treeless. Larix laricina is frequent on peat, 

 especially in wooded fens. Along rivers grows balsam poplar {Populus 

 balsamifera). All four tree species occur throughout the Boreal (and Boreo- 

 nemoral) zones. The other Boreal trees are confined to certain parts of the 

 Sub-Arctic, not reaching its northern outskirts everywhere. The sub-zone 



