28 BRITISH FOREST TREKS 



the spruce on the Harz, the beech on the Soiling and I Krister, 

 and in a less marked degree the silver fir in Thuringia and 

 on the highlands of Southern Germany, on account of their 

 great transpiration through the leaves, thrive better in moist 

 localities than in those exposed to summer drought, and can 

 often be reproduced there by sowing in the open without re- 

 quiring nurses as at lower elevations. In mountainous tracts 

 snowfall is apt to cause branches to break off, so that brittle 

 woods like Scots pine are not the species best adapted for 

 forming forest trees. In localities exposed to violent winds 

 shallow-rooted species, particularly spruce, are liable to 

 be thrown as windfall. 



2. Requirements as to soil may be estimated from three 

 points of view, namely, as regards depth, soil-moisture, and 

 mineral strength generally, and it must be borne in mind 

 that under all circumstances a due admixture of good 

 humus or mould is benefical to all classes of soil, and to the 

 general development of forest growth. 



The disintegration of the rocks must necessarily be 

 carried to such an extent as will admit of the penetration of 

 the root-system. The majority of trees require for their 

 growth soils varying from i to 3 feet in depth, and 5 to 6 

 feet may be taken as the greatest depth ever actually re- 

 quired even by the oak. Depth of soil, however, is beneficial 

 even to trees having shallow root-systems, as it enables their 

 roots to ramify more easily, and thus tends to produce 

 longer development of the bole or stem. 



As to formation of the root-system, some species develop 

 a tap-root, which is either permanently retained or becomes 

 transformed into a deep heart-shaped root with strong 

 ramifications as in the oak, elm, Scots pine, silver fir, 

 maple and sycamore, ash, chestnut, lime, and larch ; 

 others have no pronounced tap-root, but develop strong 

 side-roots which penetrate the soil to a moderate depth, as 



