12] VEGETATIONAL TYPES OF TEMPERATE LANDS 345 



its broad-leafed faciations of Birch or facies of Aspen) occupies 

 most of the northernmost beh of forested terrain around the cool- 

 temperate and boreal shoulder of the globe. Not only do they form 

 the northern, but in many places also the altitudinal, limits of tree 

 growth, extending southwards through often some 15-20 degrees of 

 latitude from this northern limit, with outliers or tongues still 

 farther south — for example in the eastern and western United States 

 of America. There are also important outliers in the mountains 

 of central and southern Europe and Asia {cf. Fig. 83, B), In addition, 

 the Pines are highly developed in area as well as species in Mexico 

 and throughout much of the Caribbean region, and, with other 

 genera of Conifers, are important far south in Central America and 

 the Mediterranean region, though these vegetation-types scarcely 

 belong to the above series. For in general the most characteristic 

 and extensive needle-leafed coniferous forests are developed chiefly 

 between the 45th and 70th parallels of north latitude. Nor, in view 

 of the very limited persistence of ice-free land at corresponding 

 latitudes in the southern hemisphere, is it surprising that such forests 

 are not paralleled there, the austral Conifers, although evergreen, 

 being commonly broader-leafed and more warmth-loving (or at least 

 far less cold-resistant). 



Except when deciduous trees or shrubs are plentiful, there is 

 relatively little difference in the appearance of the northern coniferous 

 forest at different seasons — apart, of course, from lying snow which 

 characterizes much of this belt more or less throughout the winter. 

 The climate is cool, with the winter extremely cold in the continental 

 regions ; indeed most of the lowest temperatures ever recorded have 

 been within this belt in the interior of the great northern continents. 

 In view of this frigidity, the absolute humidity need not be high 

 for the climate to remain relatively moist, with fairly regular pre- 

 cipitation throughout the year. The soil is generally poor and of 

 glacial origin. Ignoring most of the southern outliers, the following 

 five main types of northern coniferous and allied forests may be 

 recognized. 



I. The usually mixed coniferous forests occupying most of the 

 boreal forested parts of Eurasia and North America, dominated by 

 various assortments (or occasionally a single species) of Spruce, Fir 

 {Abies spp.). Pine, and Larch. The precipitation is usually between 

 25 and 100 cm. (approximately 10 and 40 inches) per annum and 

 the mean temperature of the warmest month above 10° C. (50° F.), 

 though the summer is relatively short. In eastern North America 



