204 THINNING. 



about thirty years old, after which it is more variable 

 and less distinct. 



Thinning, then, as may well be concluded, is a very 

 important operation, and one that ought only to be 

 conducted by men of experience and sound judgment, 

 and no others. The benefits of grouping, too, over 

 th^t of general mixing, is a branch of forestry by far 

 too little studied; and while one would think every 

 one must see and behold the objects immediately be- 

 fore them, yet as a matter of practice many men go 

 on in regard to thinning as if it were either of no 

 importance whether well or ill done, or of no dif- 

 ference which. It might be of no small interest and 

 instruction to those who have leisure to test the state 

 of the atmosphere of a plantation before and after 

 being thinned at the different seasons of summer, 

 winter, spring, and autumn, with one barometer at 

 the surface of the ground, and another several feet 

 above it, and also to test the temperature of the dif- 

 ferent kinds of trees at their different stages of growth, 

 from the sapling to the mature old tree. 



