VOLUME GROWTH. 59 



which have been raised in a crowded wood, are gradually 

 given more growing space. Such an opening out can, 

 provided the period of height growth has not come to an end, 

 produce a revival of the diameter increment, after its 

 maximum has been passed, due to an increased leaf surface, 

 or to a greater intensity of action, even if the leaf canopy 

 is not materially extended. This revival of diameter growth 

 generally lasts for a number of years, differing according 

 to species and quality of locality, when it gradually dies away 

 again. Nor does a tree profit by an excessively large leaf- 

 surface, because there is a limit, beyond which a tree cannot 

 assimilate and convert into wood the nourishing elements 

 available to it. 



Where both great height and diameter growth are wanted, 

 it is best to keep the wood crowded during youth, and to give 

 only a moderate growing space to each tree until towards the 

 end of the principal height growth, when the growing space 

 of each remaining tree should be gradually increased, so 

 as to develop more extended crowns and greater diameter 

 growth. This is only possible while height growth is still 

 going on ; once that has stopped, the thinning out will not be 

 followed by any appreciable extension of the crowns, which 

 can only be produced by transferring to it the energy of 

 height growth. The possibility of such a transfer is longest 

 preserved in silver fir, spruce, oak, and beech. 



4. Volume Growth. 

 The increase in volume depends on both height and 

 diameter growth, and that method of treatment which 

 promotes each in due propoi'tion, must ultimately yield the 

 largest volume ; in other words, woods should be neither too 

 crowded, nor too open. In the one case thin tall trees, and in 

 the other short thick trees would be produced. The most 

 favourable density of the crop can only be ascertained by 

 accurate statistics. General experience has shown that the 

 greatest volume is ultimately obtained, if the woods are 



