THINNING AND PRUNING 131 



a nurse, however, thinning is often practised at an early 

 age to meet estate requirements, and no pretence is made of 

 regarding it as a sylvicultural operation. Where poles and 

 fencing are required for estate use, few proprietors or agents 

 make any scruple of spoiling a young plantation in order to 

 obtain the material required. No doubt, extreme measures 

 are rarely taken, and the line is drawn at a point which 

 many foresters would term " a good thinning." But, as we 

 shall see presently, first-class timber does not result from any 

 haphazard method of thinning, which varies between the 

 removal of 25 to 50 per cent, of the total crop before height- 

 growth has culminated ; and it has always seemed to us a 

 more sensible proceeding to clear a part of the plantation right 

 off, when necessary, than to spoil the whole crop in order to 

 obtain a few pounds' worth of poles. It frequently happens 

 that poles of a certain size are wanted, and we know cases 

 where the whole of the best trees in a plantation have been 

 cut out to obtain them, leaving little but the weaker and 

 partly suppressed individuals to stand for the crop. Such 

 instances are only typical of the manner in which British 

 woods are made subordinate to other interests. 



The principles which underlie the practice of correct 

 thinning are extremely simple, and if it were only possible to 

 avoid all thinning which does not make for the ultimate good 

 of the crop, any man in possession of them has no excuse for 

 spoiling a plantation. 



The cubic contents of a tree depend upon its length and 

 mean transverse area. The former is produced by height- 

 growth, the latter by stem-growth, or what may be termed 

 ring-breadth. The object of thinning may be said to be 

 that of maintaining these two factors in their proper pro- 

 portion. With little or no thinning, and with trees of the 

 same species and age, height-growth in a thick plantation 

 is usually increased up to a certain period in the life of the 

 trees, while ring-breadth gradually decreases until it reaches 

 its minimum. The only uncertain element in this process is 

 the difference due to individual growth, and it is upon this 

 difference that the prolonged existence of a self-thinned planta- 

 tion or group depends. All organisms living in a crowded 

 state, and for which the available space is only sufficient 



