AMPHI-ATLANTIC ZONATION, NEMORAL TO ARCTIC 1 1 1 



temperate, fairly moist conditions, and the formation of a humus layer of the 

 mull type and a brown forest soil profile, as is typical of most stands of 

 genera such as Fraxiims, Acer, Ulmus, Tilia, Fagiis, and certain sections of 

 Que re us. 



The Nemoral zone is discontinuous (since Quaternary time) but its three 

 parts, in eastern North America, Europe and the Far East, are remarkably 

 similar in spite of considerable climatic difference. Each of the three parts 

 shows a south-north subdivision into two or more biotic regions, but these 

 conditions, although indicated on the maps. Figs. 2 and 3. are not dealt with 

 further in this paper. 



With reduced rainfall and increased continentality, the Nemoral regions 

 change into Steppe or Prairie regions. The usually quite extensive ecotones 

 include the warmer parts of the Woodland Steppe regions (European Russia, 

 and the Middle West of the U.S.A.). 



THE BOREO-NEMORAL ZONE 



Between the three parts of the Nemoral zone and the true Boreal zone, 

 transitional biotic regions occur, here called Boreo-nemoral. They occupy a 

 considerable width in Europe and in the Far East (Manchuria and Amur 

 districts) but the American Boreo-nemoral region is quite narrow. As this 

 part of the zonation is frequently misunderstood, it is desirable to state more 

 precisely what areas belong here and thus correspond on both sides of the 

 Atlantic. 



Because ofearlier abundance ofwhite pine (PrnM^^/ro^M^) and the occurrence 

 of other conifers (P. resinosa, Tsuga eanadensis. Thuja occidentalis), the 

 Great Lakes-St. Lawrence area has sometimes been regarded as representing 

 this zone in America, but this is only partly correct. The above-mentioned 

 conifers are essentially non-Boreal, and (except Thuja) do not reach much 

 farther into the Boreal zone than do several of the Nemoral hardwoods 

 (e.g. Fraxinus nigra, Ulmus americana, Populus grandidentata, Betula lutea). 



The Boreo-nemoral zone is met with a short distance north of the St. 

 Lawrence and Ottawa Rivers, e.g. at St. Donat and Maniwake. In Quebec 

 the change is abrupt due to the rise in level from the Paleozoic Ottawa-St. 

 Lawrence valley to the uplands of the Pre-Cambrian Shield. The difference in 

 bedrock and Quaternary deposits greatly amplifies the combined effects of 

 latitude and altitude on vegetation. The shift of dominance from exacting, 

 mainly deciduous trees to hardy, less demanding Boreal conifers is thus 

 comparatively abrupt and was evidently still more impressive before so much 

 of the latter were cut. 



Farther west the Boreo-nemoral zone is broader, extending also south of 

 the Ottawa River (Petawawa, Algonquin Park), and crossing Lake Superior 

 to reappear in southeastern Manitoba and northeastern Minnesota. 



