FOEESTKY GRAVES. 259 



itself. If the forester had not found forests in nature, he would 

 have had to create forests artificially in order to accomplish his prac- 

 tical purpose, since it is only through the control and regulation of 

 the natural struggle for existence between trees in the forest that the 

 forester is capable of managing it for the practical needs of man. 

 Thus from the very nature of his dealings with the forest the forester 

 was forced from the beginning to consider the forest not merely as an 

 aggregation of individual trees but as communities of trees — tree 

 societies — and first, from purely utilitarian reasons, developed a 

 science upon which the practice of silviculture now rests. 



Forestry as a natural science, therefore, deals with the forest as a 

 community in which the individual trees influence one another and 

 also influence the character and life of the conununity itself. As a 

 community the forest has individual character and form. It has a 

 definite life history; it grows, develops, matures, and propagates 

 itself. Its form, development, and final total product may be modi- 

 fied by external influences. By abuse it may be greatly injured, and 

 the forest as a living entity may even be destroyed. It responds 

 equally to care and may be so molded by skillful treatment as to 

 produce a high quality of product, and in greater amount and in a 

 shorter time than if left to nature. The life history of this forest 

 communit}'^ varies according to the species composing it, the density 

 of the stand, the manner in which the trees of different ages are 

 grouped, the climatic and soil factors which affect the vigor and 

 growth of the individual trees. The simplest form of a forest com- 

 munity is that composed of trees of one species and all of the same 

 age. When several species and trees of different ages occupy the same 

 ground, the form is more complex, the crowns overlapping, and the 

 roots occupying different layers of the soil. Thus, for instance, 

 when the ground is occupied with a mixed stand of Douglas fir and 

 hemlock, the former, requiring more light, occupies the upper story 

 and because of its deeper root system extends to the lower-lying 

 strata of the soil. The hemlock, on the other hand, which is capable 

 of growing under shade, occupies the under story, and, having shal- 

 low roots, utilizes largely the top soil. 



There are forest commimities, such, for instance, as those typical 

 of northwestern Idaho, where western larch, Douglas fir, western 

 white pine, white fir, western red cedar, and hemlock all grow to- 

 gether. Such a forest is evidently a very complex organism, the 

 stability of which is based on a very nice adjustment between the 

 different classes and groups occupying the same ground. Any change 

 in one of these classes or groups must necessarily affect the other. 

 If, for instance, in the Douglas fir-hemlock forest the Douglas fir is 

 cut out, the remaining hemlock trees are likely to die out because their 

 shallow roots are left exposed to the drying effect of the sun and wind. 



