32 BRITISH FOREST TR1 .1 -.> 



requirements. The immense improvement which takes place 



in soils under dense forests of beech and spruce is a striking 

 proof of the invaluable soil-improving qualities of mould. 



3. Differences of Forest Trees as to Shape. The essential 

 characteristic of a tree as compared with a shrub is that a 

 main stem, trunk, or bole is developed above the root-system, 

 and branches are thrown out to form a crown only at some 

 distance above the soil. Some species of forest trees tend 

 more to the development of a long straight bole than others, 

 as for example the conifers generally in comparison with 

 broad-leaved deciduous trees. The individual tendencies of 

 every species are further dependent on several factors 

 influencing them, of which the principal are the growing 

 space allowed to each individual, the age of the forest, and 

 the nature and quality of the soil and situation. 



The natural tendency to assume a certain, more or less 

 constant, form has free indulgence only when the individual 

 tree has full enjoyment of light, warmth, and air. Some, by 

 means of the development of the terminal bud of the main 

 axis always taking place with much greater rapidity than the 

 shoots of side branches, assume long straight stems with a 

 more or less conical disposition of foliage, and have a de- 

 cidedly stronger tendency upwards than sidewards ; whilst 

 in regard to others the terminal shoots of the branches 

 compete with that of the ascending axis, with the result that 

 the stem remains short and stunted, the crown low, and the 

 branch development relatively great. 



According to the tendencies exhibited in one or other of these 

 directions, the forest trees have been classified as follows by Gayer : 

 Forming undivided stems Spruce, silver fir, larch, Weymouth pine ; 

 more or less brandling towards summit Scots pine, alder, beech, 

 oak (sessile), black poplar, Cembran pine ; someivhat greater tendency 

 to branc king ash, maple, sycamore, elm; decided tendency to brandl- 

 ing at comparatively small height above soil oak (pedunculate), lime, 

 chestnut, hornbeam, mountain pine (op. cit. pp. 36, 37). 



