graves: place of forestry among sciences 49 



The first social phenomenon in a stand of trees is the differen- 

 tiation 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 differentiation into dominant and suppressed trees 

 takes place particularly in youth 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 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 hght, 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: 



At 20 years of age 4 sq. ft. 



« 40 " " " 34 " " 



a go " " " 110 " " 



a 100 " " " 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 

 universal in forests everywhere. 



Another peculiarity that marks a tree community is the dif- 

 ference in seed production of trees which occupy different posi- 

 tions 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 desig- 

 nated 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, 



