CHAP, ix.] Tending of Woods 185 



2, Thinnings in Pole-forest and Young Tree-forest. 



Under thinnings are understood all operations for the 

 removal of unnecessary species or individuals in timber crops, 

 dating from the time that the outlay thus occasioned is 

 covered by the returns obtained for the material removed, and 

 thence onwards throughout the pole-forest and the tree-forest 

 stages of growth, till a commencement is made of the clear- 

 ances for reproduction or utilization, or until partial clearances 

 are made, after the chief growth in height has been completed, 

 for the more rapid development of large-girthed boles with 

 good top-diameter. 



The ultimate quantitative and qualitative outturn from 

 woodland crops depends much more on the proper conduct 

 of the thinnings than on the preliminary operations of weeding 

 and clearing. Practically, there is generally a period, of shorter 

 or longer duration, in which the thickets formed from natural 

 reproduction or from sowing are almost impenetrable ; and in 

 mixed forests, in which the more valuable subordinate species 

 occur individually, and not in patches, this is often the most 

 critical period for these latter kinds of trees. 



The object of thinning any crop is to stimulate and to assist its 

 development so that the aim of the proprietor may be attained 

 as completely and as soon as possible, without necessitating any 

 such interruption of the canopy as may prejudice either the 

 growth in height of the crop or the productive capacity of the 

 soil. The crops which stand most in need of thinning, and of 

 a frequent repetition of the operation, are those in which the 

 individual stems are all of about the same age ; as the natural 

 struggle for individual existence is then more keen and pro- 

 longed than where some plants of advance-growth have from 

 the very outset won an advantage. In this process of natural 

 selection four classes of stems become distinguishable, viz. 



