POEESTRY — GRAVES. 263 



change materially the present methods of cutting in the white pine 

 and Douglas fir forests, to the mutual advantage of the Government 

 and of the logging operators. 



I shall give briefly a few other illustrations of the life of the 

 forest which stamp it as a distinct plant society. 



The first social phenomenon in a stand of trees is the differentiation 

 of individuals of the same age on the basis of differences in height, 

 crown development, and growth, the result of the struggle for light 

 and nourishment between the members of the stand. A forest at 

 maturity contains scarcely 5 per cent of all the trees that have 

 started life there. Yet the death of the 95 per cent is a necessary 

 condition to the development of the others. The process of differen- 

 tiation into dominant and suppressed trees takes place particularly 

 in 3^outh and gradually slows down toward maturity. Thus, in some 

 natural pine forests, during the age between 20 to 80 years, over 

 4,000 trees on an acre die ; whereas at the age between 80 to 100 years 

 only 300 trees die. With some trees this natural dying out with age 

 proceeds faster than with others. Thus in pine, birch, aspen, and all 

 other species which demand a great deal of light, the death rate is 

 enormous. With spruce, beech, fir, and species which are satisfied 

 with less light, this process is less energetic. The growing demand 

 for space with age by individual trees in a spruce forest may be 

 expressed in the following figures : 



Square feet. 

 At 20 years of age 4 



At 40 years of age 34 



At 60 years of age 70 



At SO years of age 110 



At 100 years of age 150 



If we take the space required by a pine at the age between 40 

 and 50 years as 100, then for spruce at the same age it will be 87, 

 for beech 79, and for fir 63. This process of differentiation is uni- 

 versal in forests everywhere. 



Another peculiarity that marks a tree community is the difference 

 in seed production of trees which occupy different positions in the 

 stand. Thus, if the trees in a forest are divided, into five classes 

 according to their height and crown development, and if the seed 

 production of the most dominant class is designated as 100, the seed 

 production for trees of the second class will be 88, for the third class 

 33, for the fourth class only 0.5 per cent; while the trees of the fifth 

 class will not produce a single seed, although the age of all these trees 

 may be practically the same. The same struggle for existence, 

 therefore, which produced the dominant and suppressed trees works 

 toward a natural selection, since only those which have conquered in 

 the struggle for existence and are endowed with the greatest in- 

 dividual energy of growth, reproduce themselves. 



