62 DEVELOPMENT OF FOREST TREES. 



10,000 cubic feet ; if an acre can hold 50 mature oak trees, 

 each \vith a vohime of 150 cuhic feet, the total volume per 

 acre will be only 7,500 cubic feet, or 2,500 cubic feet less 

 than in the case of silver lir. 



The number of trees which find room on an acre of ground 

 depends chiefly on 



(a.) The light requirement of the species. 



{h.) The tendency of the species to develop the crown in 

 preference to the stem. 



(r.) The quality of the locality. 



Hence, an acre stocked w4th the light demanding birch, 

 ash, or spreading oak, contains a smaller number of trees and 

 a smaller volume than an acre stocked with beech. Again, 

 larch, and Scotch pine woods contain fewer trees and a 

 smaller volume per acre than silver fir and spruce woods. 

 The number of trees per acre on a fertile soil is consideral)ly 

 smaller than on an inferior soil. 



Full details on this question will be found in Volume III. of 

 this Manual. In the meantime the accompanying diagram 

 (p. 61) will give a general idea of the number of trees found on 

 localities of the first quality in the case of spruce, silver fir, 

 beech, and Scotch pine. 



5. Iniration <>/ Li/r. 



A great dift'erence exists in the age which the various 

 species attain ultimately. If grown under conditions which 

 are in harmony with their requirements, the yew lives for 

 more than 1,000 years, the oak comes often near that age, if 

 it does not exceed it ; lime, elm and sweet chestnut reach and 

 surpass an age of 500 years; beech reaches a similar age 

 under favourable circumstances, but ordinarily both beech 

 and silver fir die before that age. A limit of 300 years may 

 be assigned, to ash, maple, sycamore, spruce, larch, Scotch 

 pine and hornbeam ; while aspen, birch, alder and willow- 

 live, under ordinary conditions, little beyond 100 years. 



In forestry the trees are, as a rule, cut over Iwig before 



