AMPHI-ATLANTIC ZONATION, NEMORAL TO ARCTIC 1 1 3 



belongs in the Boreo-nemoral (Jalas, 1957), which further comprises the former 

 Baltic States, northeastern Poland, and large parts of western and central 

 European Russia east to the Urals. The northern limit of Quercus robur is 

 generally considered as its boundary towards the Boreal zone proper, but in 

 Russia the latter boundary is drawn some distance farther south (Lavrenko 

 and Sochava, 1954). 



From Manitoba westward, and east of the Urals, the Nemoral zone is 

 absent, being replaced by prairies (steppes). The Boreo-nemoral zone in 

 turn is replaced by a transition zone between the Boreal coniferous forest 

 zones and the steppes, a zone where both most Boreal conifers and Nemoral 

 hardwoods are absent or scarce. Betula and Popiilus remain, and aspen 

 groves are particularly characteristic {P. tremuloides and P. tremula, respective- 

 ly). In the Canadian Prairie provinces this zone is represented by the Aspen- 

 Oak Section (with Quercus tnocrocarpa, U/mus americana, Acer negundo, 

 etc.) and the Aspen Grove Section of Rowe (1959). The west Siberian counter- 

 part is divided into a northern region of "parvifoliate forest" (Lavrenko and 

 Sochava, 1954) and a Woodland Steppe region between this and the treeless 

 Steppe. 



THE BOREAL ZONE 



Encircling the globe south of the Arctic there is a Boreal zone (Hare, 1954) 

 where forests are usually formed by a very limited number of species belonging 

 to a few coniferous and hardwood genera : Picea. Larix, Pinus, Abies, Betula, 

 Populus, Ahuis. In addition, species of Salix, Sorbus {aucuparia type), and 

 Prunus {padus type) reach tree size. Only very few of the species of these 

 large genera are actually Boreal, as emphasized by Hare {loc. cit.). Some of 

 these, e.g. the Populus species, extend much farther south; others are pre- 

 vailingly Boreal, but all of them extend south at least into the Boreo-nemoral 

 zone. This is true also of many Boreal species of smaller size. 



As expressly stated by Hare {loc. cit.) a large part of the conifer forests of 

 the world should not be included in the Boreal (or Boreo-nemoral). This is 

 true of the Pacific forests, and of the pinewoods occurring in the Nemoral and 

 still warmer zones. More related to Boreal forests are some Montane or Sub- 

 Alpine forests at the middle latitudes (e.g. in the Rockies, the Alps, Altai, etc.), 

 and the oceanic pinewoods of Scotland and westernmost Norway, but they 

 are kept separate in this paper. 



The Boreal forests, after having reached maturity, are usually made up of 

 conifers, but some areas belonging here are permanently covered by birch- 

 woods, alderwoods, or groves of poplar. The Boreal zone is also very rich in 

 bogs and fens. It comprises by far the largest part of the peatland areas of the 

 world (Fig. 1, from Sjors, 1961b). 



The Boreal zone may be subdivided into three or more east-west sectors 



