18 TECHNICAL PROPERTIES OF WOOD. 



crop, and above all, the beech, hornbeam, and pedunculate oak, 

 the boles of which when grown in the open usually subdivide 

 into boughs at a height of 15 to 20 feet. 



It follows that the ratio of the mass of timber in the bole of 

 trees to that of their crown varies according to the system of 

 forest management, and must be much greater under the high 

 forest systems than in coppice-with-standards. 



(c) Age of Tree. — In considering the amount of utilizable 

 stem-timber in a tree grown in a dense crop, it is evident 

 that during its youth branch wood considerably predominates ; 

 when middle-aged, the quantity' of stem-timber has already 

 largely increased, and still more so during old age : hence when 

 closely grown, the better species of mature trees yield only 10-20% 

 of branchwood in their total wood-production. It is also easy to 

 see that the amount of rootwood increases with the age of the 

 tree. 



(d) duality of Locality. — The amount of useful development of 

 which a tree is capable depends chiefly on the kind of locality where 

 it is growing, so that it may be laid-down as a general rule, that 

 the amount of stem-timber in a tree rises and falls with the 

 quality of the locality. As a rule, the law of root-production is 

 the converse of this, so that the more favourable the soil and 

 climate, the smaller the root-system in proportion to the total 

 mass of the tree. 



[In very dry countries, as in Ivajputana in India, and New Mexico, 

 species of Frosopis develope tap-roots fifty feet and more in length, 

 with very short stems. In these regions farmers dig up the wood 



they recjuire. — Tu.] 



It may readily be conjectured that, owing to the number of 

 factors which affect the ratios betw^een the stem, branch and 

 rootwood of a tree, no constant figures can represent these 

 ratios. In order, however, to give some idea of their value, the 

 following figures, taken from observations made by Pfeil and 

 Hartig and relating to trees grown under favourable local con- 

 ditions in dense high forest woods, show the relative per- 

 centage of wood in the bole, branches and roots of different 

 species of trees. 



