326 



INTRODUCTION TO BOTANY 



Rapidly running surface water often carries away part or 

 all of the fertile soil. 1 In grasslands, meadows, and forested 

 areas surface water is retarded in its rate of flow, and conse- 

 quently does not carry away much soil. In regions that were 

 once forested and from which the timber has now been largely 



FIG. 239. Erosion of the soil following removal of the forest 



This land was covered with a heavy pine forest and had a rich soil, which was 



held upon the forest floor. When the timber was removed, erosion soon cut 



ditches through the pasture land, and part of the rich soil was washed away 



removed, the surface water soon erodes ditches (fig. 239), 

 which, with rapidly deepening channels and developing tribu- 

 taries, will in a few years carry away much of the fertile soil 

 of the forest floor. After forest fires, which themselves destroy 

 much of the humus of the forest soils, the surface water, 

 which is no longer retarded and absorbed by humus, flows 



ff Soil Erosion," Bulletin 71, Bureau of Soils, U.S. Dept. Agr. 



1911. 



