110 HUGO SJORS 



BIOTIC REGIONS, ZONES, AND BELTS 



Individual elements of climate thus fail to give the same pairs of corres- 

 ponding points. But vegetation, being an integration of cHmatic as well as 

 other factors, may show the total effect of climatic impact on life better than 

 single variables do. 



The vegetational unit most suitable for such a comparison is the regional 

 (vegetation) complex (term by Du Rietz, in mimeographed lectures) which 

 occupies a vegetation region, in the sense used by many phytogeographers, 

 notably those of Scandinavia (cf. Du Rietz, 1930, pp. 497-502). If we include 

 animal life and environment, and thus refer to the whole ecosystem — a 

 heterogeneous ecosystem covering vast expanses of land — we may speak of a 

 hiotic region (Sjors, 1955, p. 163). Biotic regions situated in different longitudinal 

 sectors of the globe may occupy corresponding positions as to zonation in 

 latitudinal direction. They are regarded as parts of the same biotic zone 

 (cf. Rousseau, 1952, p. 437). In mountainous countries, biotic regions homolo- 

 gous in their altitudinal position constitute a biotic belt (cf. Du Rietz, 1930, 

 p. 499). There are cases when mountain biotic belts correspond to, or even 

 gradually merge into, biotic zones of the lowland farther north (or south, in 

 the Southern Hemisphere). 



In forested biotic regions, forests are usually more important than other 

 kinds of vegetation. Leading tree species become significant for the delimita- 

 tion of these regions. Usually the dominance, although only partial, of a tree 

 species is more important for this purpose than a scattered occurrence. 

 However, sub-regions within the Boreal coniferous zone (see below) must 

 often be determined from the areas of subordinate species, because the 

 dominant conifers are the same. Also, criteria taken from the physiognomy 

 and total composition of vegetation may be adduced for similar purposes 

 (Kujala, 1936: Hare, 1950, 1954, 1959; Kalela, 1958, 1961 : Ahti, 1961). 



THE NEMORAL ZONE 



Following Regel (1950, 1952) the author prefers to designate as Nemoral 

 the three great parts of the Northern Hemisphere where temperate deciduous 

 trees are prevalent. According to Regel (1952, p. 38) the term "Nemoral" was 

 introduced by Russian authors. Regel includes the Boreo-nemoral zone in the 

 Nemoral zone as a special sub-zone. The frequently used term "deciduous 

 forest zone" is open to some criticism. Thus, considerable coniferous forests 

 (pines, etc.) occur within this zone, particularly in North America and Japan. 

 There exist also deciduous forests of quite different types, e.g. those in the 

 Sub-tropics and the seasonally moist Tropics. Nor should the deciduous 

 birchwoods of Sub-Alpine Fennoscandia and Kamchatka be included. 

 Strictly speaking, also Larix is deciduous. The word Nemoral is free from such 

 objection, and emphasizes the adaptation of the vegetation and flora to mild- 



