CHAP, x.] Stimulation of Increment 211 



or more of the crop be thus prematurely utilized it must 

 certainly be considered a partial clearance. 



That such measures undoubtedly do lead to a stimulation of 

 the annual increment is a fact not only abundantly shown by 

 practical experience, but also proved more than half a century 

 ago by the more eminent sylviculturists of Germany, C. Heyer, 

 Th. Hartig, Nordlinger, and others. These authors showed 

 conclusively that a stimulation of the increment on individual 

 stems took place, as the natural result of all such thinnings as 

 exceeded in degree the natural process of that unavoidable 

 struggle for existence in which the stronger first overtops and 

 finally suppresses the weaker individual stems, whenever such 

 free thinnings were made in forests growing in dose canopy, and 

 at an age not exceeding to any considerable extent the normal 

 periods of rotation under which the species of tree in question 

 was usually grown as a timber crop. Every now and again, 

 however, some champion steps forward to dispute what have 

 long been accepted as facts; but the plausible deductions 

 drawn from his observations are always, on closer investigation, 

 found to have some flaw. Thus, for example, he may have 

 confined his attention to the bole only, or have neglected to 

 discriminate between the direct effects of the freer exposure 

 to light and air, and the adventitious circumstances under 

 which the latter may have taken place, although these concrete 

 conditions are at times of such influence as to diminish, or even 

 to counteract, the intended results of the thinning or partial 

 clearance. 



There is generally some very easily determinable reason when 

 this latter measure fails to produce more energetic increment. 

 The thinning or partial clearance may, for example, have been 

 carried so far as actually to have interfered with the normal 

 functions of the root-systems and the crowns of foliage of the 

 individual trees left forming the crop. These nouveaux riches 

 may often require some little time to settle down and accustom 

 themselves to their altered circumstances ; and the first form 



P 2 



