HERMAN H. CHAPMAN 19 



seedlings may be filled with grass, weeds, or shrubs, and 

 with these the seedling must compete both for moisture 

 and light. 



As the seedlings grow in height, their crowns spread 

 and interfere more and more, casting a shade which first 

 kills out the grass and weeds and many of the bushy plants, 

 and then begins to cause the death of the lower branches 

 of the seedlings themselves. Almost at once, in the more 

 crowded portions, the weaker seedlings or those which did 

 not get so early a start as the others, begin to die out 

 through the competition of their more vigorous neighbors. 

 As the trees grow in height, more and more of them are 

 killed in the struggle. This diminution in numbers is nat- 

 ural and inevitable. There is not room for more than a 

 very small per cent of the original stand, and the strong- 

 est are best able to appropriate the growing space. A stand 

 of seedlings fully stocked, may have from 5,000 to 20,000 

 plants per acre. The same stand at maturity may not re- 

 tain more than 100 trees. As long as the growth in height 

 continues there will be a correspondingly rapid reduction 

 in numbers. After the trees have attained their principal 

 height growth, the numbers still diminish, but much more 

 slowly. 



The Forest Floor and its Effect on the Soil. — As soon 

 as a complete cover is formed by the crowns the soil is 

 shaded and grass is killed out. This very much reduces the 

 evaporation, since grass and weeds use a much larger 

 amount of water from the surface soil than woody plants, 

 a fact which gives them their strongest hold in competition 

 with tree seedlings. The annual fall of leaves or needles 

 begins to accumulate and soon forms a mat of litter which 

 still further checks evaporation. Since the agencies which 

 harden a soil are sun, wind and rain, while opposed to these 

 frost and the growth of roots tend to make soil loose and 

 mellow, we find soils protected by a forest cover and a leaf 

 litter, becoming soft and capable of rapidly absorbing the 



