CHAPTER VIII. 



PARTIAL CLEARANCES AND UNDERPLANTING. 



Partial Clearances for the production of mature timber of 

 large girth, are often made at intervals before the final 

 felling. 



Under certain conditions this policy can be strongly 

 recommended. 



It consists in a succession of very heavy thinnings remov- 

 ing from i to J or more of the smaller trees forming the crop. 

 These heavy thinnings should not take place until after the 

 principal height growth has ceased, as to seriously check 

 height growth would be very bad practice. In making these 

 partial clearances the canopy is broken, and the trees which 

 are left standing enjoy a maximum amount of light and air, 

 with the result that in practically all cases a greatly enhanced 

 increment per individual stem takes place, provided always 

 that the trees are still vigorous, and that senile decay has not 

 yet begun. 



Often the width of annual rings will be doubled. 



The actual reason for this enhanced increment is some- 

 what open to discussion, but probably it is due to the follow- 

 ing reasons : 



(1) The increased intensity of light will render the 



assimilation of carbonic acid gas (CO 2 ) more active, 

 through the existing foliage of the crown. 



(2) Dormant buds will be flushed and new foliage pro- 



duced ; and hence increased assimilation. 



(3) Food supplies from the soil are required to nourish a 



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