INCREASED GROWTH. METHOD OF DETERMINATION 363 



TABLE LVI 



Current Growth, Loblolly Pine, by Diameters 



280. Increased Growth. Method of Determination. The effect on 

 diameter growth of trees of releasing their crowns by removal of a portion 

 of the stand in logging cannot be predicted accurately on stands pre- 

 vious to cutting. The release of additional supplies of soil moisture 

 and fertility, increased light and other favorable influences, is not deter- 

 minative. The ability of the tree to take advantage of these favorable 

 circumstances varies with the age and vigor of the individual crown. 

 When trees have passed a certain relative age and have become over- 

 mature, they no longer respond as vigorously, and some species make 

 no response at all, while others, such as lodgepole pine, seem to retain 

 the power of increasing their growth throughout their life. Some trees 

 are not released in partial cuttings; hence increased growth cannot 

 be expected except on those trees which are benefited and have the 

 power of respon.se. 



The factor of increased growth after cutting must therefore be meas- 

 ured by studying trees growing on tracts which have been cut over at 

 some previous period coinciding in length with the period for which 

 the prediction of growth is desired. This may be 10, 20 or 30 years. 

 Increase in growth due to cutting tends to disappear as the stand 

 adjusts itself to the new conditions and closes its crown canopy. The 

 competition of different species in a mixed stand and their ability to 

 occupy space released by cutting, determines which of these species 

 will benefit in form of increased growth. 



