THE FOREST ORGANISM. 



227 



taller than others, is due to their ability to raise water. The most 

 remarkable in this respect are the California redwoods, the big trees, 

 and certain eucalypts in Australia. 

 This inability of trees to grow above a 

 certain height results in a flattening of 

 the crown, Fig. 73, and at this stage, 

 the trees struggle against each other by 

 crowding at the side. 



Inasmuch as trees grow more sen- 

 sitive to shade with advancing age, the 

 taller trees have the advantage. Each 

 survivor is one of a thousand, and has 

 outlived the others because it is best 

 fitted for the place. 



This fact has its effect upon the next 

 generation, because it is these dominant 

 surviving trees which bear seed most 

 abundantly. After the tree has finished 

 growing in height and diameter most 

 vigorously the pole stage and proved 

 to be fitted for the place, its energy is 

 largely spent in raising seed. As this 

 process goes on generation after genera- 

 tion, only the best coming to maturity 

 in each, the poorer sorts are sifted out, 

 and each region and continent has 

 those species best fitted to meet the con- 

 ditions of life there. 



This is the reason why exotics are 

 very likely to be sensitive and perhaps 

 succumb to influences to which native 

 trees are immune. 



Standards and veterans are the sur- 

 vivors of all the lower stages, each of 

 which has had its especial dangers. If 

 left alone, the tree gradually dies and 

 at last falls and decays, adding somewhat to the fertility of the forest 

 soil. From the point of view of human use, it would far better 

 have been cut when ripe and turned into lumber. It is a mistake to 



r. 73. Flattened Crown of 

 Red Pine. U.S. Forest Service. 



