62 



upper part of the bole; whereas in isolated trees it is to be found 

 much lower down. In canopied crops growing in favourable soils 

 and localities the increment of sectional area is almost the same 

 throughout the entire length of the stem; in unfavourable soils and 

 localities and in the case of all isolated trees, whatever the nature 

 of the soil and locality, it steadily decreases from below upwards. 

 D. Bate of increase of volume. 



Increased mass is the result of the co-operation of three factors — 

 increase of height, increase of girth and augmentation of the 

 form-factor. In early youth, in spite of the great width of the 

 concentric rings of woody growth, the increment of volume is 

 small ; it reaches an important figure only when the crown has 

 acquired some development, and the stem, by its increased height 

 and girth, presents a sufficiently extended surface for the deposit 

 of new woody growth. After this period the rate at which the 

 volume increases rises rapidly to its maximum. In Europe this 

 maximum is attained at the age of 50 — 70 years in the case of 

 quick-growing species in suitable soils and localities; at. the 

 age of 100 — 120 years in the case of slow-growing species under 

 unfavourable conditions ; and at a very advanced age by trees 

 standing out in the open, or situated on high exposed ridges or at 

 great elevations. Once at its maximum, the annuiil rate of increase 

 remains more or loss steady for a long time, after which it declines, 

 but at a less rapid rate than that at which it rose. 



The mean annual increment of the individual tree, as a rule, 

 attains its maximum only at a very advanced age, generally beyond 

 that of ordinary exploitability. Even in canopied crops the maxi- 

 mum is not reached by the dominant and over-topping trees before 

 the age of 1^0 — 140 years. Trees growing out in the open, and 

 individuals of species which develop slowly during their youth, 

 attain it much later; while in high mountainous regions many trees 

 as much as 300 years old may be found which have not yet entered 

 upon that stage. 



5. General remarks on the growth of the crop. 



The course of development and the accretion of volume in timber 



crops depends not only on the species, soil and locality, but also on 



the treatment and system of working adopted. In respect of one 



and the same species the amount of production is influenced chiefly 



