RELATIONS OF HEIGHT GROWTH AND DIAMETER GROWTH 367 



survives with so greatly reduced a rate of growth in height that this 

 rate is no indication of the capacity of the species nor of the quahty 

 of the site. Normal heights, both as to growth for a current period 

 and total height attained at a given age, can be determined only for 

 trees which have grown throughout then- life cycle free from suppression 

 or overtopping. 



283. Relations of Height Growth and Diameter Growth. Although 

 both growth in height, and growth in diameter, are responsive to site 

 quahty, they follow different laws in response to density of stand and 

 crown class. As the result of the tendency for all trees in even-aged 

 stands of intolerant species either to maintain the average height growth 

 of the stand or to die, the relation between diameters and heights for 

 individual trees is not consistent. The diameter growth of dominant 

 trees is relatively faster than the height growth, while the height growth 

 of the trees in danger of being overtopped, although a little slower than 

 that of these dominant trees, is still relatively faster than their diam- 

 eter growth which falls off in proportion not to height but to spread 

 of crown. For this reason a dominant tree of a given height will be a 

 stout tree with low form quotient (§171) while a suppressed tree in 

 the same stand will be slender and cylindrical. 



These relations are emphasized when trees of different stands are 

 compared on the basis of diameter. Dominant trees of a given 

 diameter will be comparatively short, while suppressed trees of this 

 diameter will be 

 tall and slender. 

 When the ages 

 of these trees are 

 compared, the 

 short dominant 

 tree is found to 

 be a young tree, 

 compared with 

 the suppressed 

 tall tree, which is 

 much older. 



These rela- 

 tions between 

 height and diam- 

 eter of stands ^^^ 76.— Heights of trees based on diameter in three even-aged 

 and trees are stands compared with heights of dominant, intermediate and 

 shown in Fig. 76. suppressed trees of different diameters. 

 Within a given 

 age class, the curves indicate the somewhat slower growth in height 



