soil about the roots has absorbed water to a point determined 

 by its characteristics, the water then infiltrates into deeper 

 layers of soil and rock. 



Through millions of years there was developed in this 

 manner a " delicate balance" 7 between precipitation, the soil 

 and vegetative cover most favorable to the maintenance of 

 vegetable life, which is the basis of animal and human life. 



The part played by forests, grasses, and other vegetative 

 cover in the natural circulation of earth waters is of especial 

 importance. Notwithstanding disagreement among scien- 

 tists when they consider it in such aspects as influence on 

 climate, rainfall, and stream flow of large rivers, 8 the weight 

 of scientific judgment is that the influence of such cover on 

 absorption, infiltration, and groundwater storage, and on 

 regularity of the flow of creeks and small headwater streams 

 through its influence on groundwater supply, must be a 

 dominant factor in any approach to solution of the problem 

 caused by water and soil losses through excessive run-off. 

 Experiments and measurements have proved that there are 

 noteworthy differences in water and soil losses as between 

 forest or sod lands, lands given to crop rotations, and lands 

 given to continuous, cultivated single crops. 



It has been a popular belief that forests and other vegeta- 

 tive cover retard run-off and conserve water primarily be- 

 cause the humus and humified top soil absorb and hold water. 

 These layers do have an important absorptive and holding 

 capacity, although they seldom become completely saturated, 

 and it is by them that the water is immediately provided 

 which carries sustenance to the vegetative cover. But even 

 more important is the promotion of penetration to deeper 

 storage by these layers. The forest litter and the grass me- 

 chanically retard flow and hold back water for absorption, 

 their coarseness promotes penetration, they serve as a filter 

 which holds back most of the particles that might clog the 

 soil pores, and their presence as a blanket keeps the underly- 



7 W. J. McGee, Wells and Subsoil Water, Bulletin No. 92, Bureau of Soils, U. S. Depart- 

 ment of Agriculture, Mar. 26, 1913, p. 182. 



8 For a brief summary by a leading authority see The Role of Vegetation in Erosion 

 Control and Water Conservation, by W. C. Lowdermilk in Journal of Forestry, Vol. XXXII, 

 No. 5, May 1934. 



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