BRITISH FOREST TREES 213 



It has a weak root-system, weaker than that of any other 

 species ; the growing-space required by the roots is not 

 extensive, although on loose soils they spread further than 

 in tenacious or binding soils. In addition to the root- 

 system being weak and inextensivc, it is also shallow, 

 though not quite so shallow perhaps as that of the spruce, 

 for the horizontal development of the side-roots always 

 takes place at some little depth below the surface of the 

 soil. 



Requirements as to Soil and Situation. The birch is 

 more a tree of the cold, raw north, with its prolonged 

 winter, than of localities with a milder, southern climate ; 

 more an inhabitant of the lowlands and uplands, than of 

 mountain districts ; indigenous rather on sandy and loamy 

 soils, than on varieties of any very strong nature ; more 

 frequently to be found self-sown on light soils, than on 

 heavy tenacious clays or limes. Its best development is 

 attained on loamy soils. 



Both varieties can endure great cold throughout the 

 winter, and a considerable degree of warmth in summer ; 

 they excel, indeed, all other species of forest trees in this 

 power of accommodation to both extremes of climate. 

 Both, however, make considerable demands on humidity of 

 the atmosphere, those of B. verrucosa being somewhat the 

 greater. A large supply of soil-moisture is essential for the 

 proper development of B. pubescens, whilst B. verrucosa 

 requires merely freshness of soil, and is often found in 

 comparatively dry situations. 



On the whole, birch is seldom found forming forests in 

 Britain on the better soils and situations, and forest land 

 on which it is plentiful can not in general be regarded as 

 being utilised to the greatest possible advantage. 



Requirement* as to Light. The birch stands on a level 

 with the larch as the most light-loving [of all the species of 



