DIAMETER GROWTH. 57 



c. Lordlitij. 



The factors of the locality have a decided effect upon height 

 growth. It has already heen pointed out that deep, fresh, 

 fertile soils produce much higher trees than shallow, dry, 

 rocky soils. Elevation exercises also a considerable influence. 

 It may be said that every species shows its greatest height 

 growth at that elevation which offers the most favourable 

 climatic conditions for its growth ; above that elevation the 

 height growth decreases, and in many cases also below 

 it. In situations exposed to strong air currents and other 

 unfavourable influences, height growth is comparatively small. 



d. MetlKxh of Formal ion and of Treatmeni. 



They affect the height growth principally on account of 

 their effect upon the establishment and preservation of a 

 complete leaf canopy. The more complete the cover, the 

 better will be the effect upon the height growth of most 

 broad-leaved species, Scotch and -other pines; it is less pro- 

 nounced in the case of silver fir, spruce and larch. In this 

 respect the manner in which thinnings are conducted is 

 of paramount importance, a subject which is dealt with in 

 Part III. of this volume. 



3. Diameter Growth. 



Generally speaking, the increase of the diameter of the 

 stem (or bole) is, in the case of all species, fairly pro- 

 portionate to the height growth, that is to say, both height 

 and diameter growth are greatest at the same period of life. 

 In the case of light demanding species the diameter 

 increment often reaches its maximum between the 20th and 

 30th year of age, a good increment being maintained up to 

 the 50th or 60th year, when it commences to fall off'. Shade 

 bearing species and oak reach the maximum diameter 

 increment later on, but it is also longer maintained, often up 



