SILVICS g 



breakage, or other causes, seeds of trees germinate and begin 

 to grow. The kind of trees that come up here depends, as 

 has already been shown, on many factors the kinds of seed 

 trees near, the covering of the soil and moisture content, the 

 light available, etc. On the burned-over and freshly-exposed 

 mineral soils, poplar, bird cherry, and birch spring up freely; 

 on the abandoned fields, pine and spruce are especially apt to 

 appear; and on the moss-covered decaying logs of the northern 

 woods, little hemlocks, fir, and spruce seedlings start. In a few 



Fig. i. Two stands of white pine of different age classes. The one at the right is 40 years, 

 that on the left 70 years of age. 



years the growth and very existence of these seedlings are in- 

 fluenced and other changes take place. The tops of the old 

 trees may spread out and shade the openings, so that only the 

 tolerant seedlings can endure; or the remaining old stand may 

 be felled and an unlimited amount of light admitted. Under 

 this impetus certain rapid-growing species may push up to the 

 entire exclusion of the others, or these others if they are tolerant 

 of shade may be relegated to an understory of secondary im- 

 portance. On an acre of forest soil thousands of such seedlings 



