EROSION AND REVEGETATION 189 



of the plants studied. It shows a remarkable contrast in these 

 functions. In peas, for instance, the numbers of leaves are as 

 I to 27; the leaf lengths as i to 3.3; the total dry weights pro- 

 duced as I to 8.3 ; and the water used per plant as i to 4.6 — all 

 in favor of the noneroded soil. In the amount of water used 

 per pound of dry matter produced, on the other hand, the ratio 

 is reversed, being as 1.8 to i on the eroded and noneroded soils, 

 respectively. The general development of the plants and the 

 water requirements of native bromegrass and wheat are similar 

 to those of peas. In all the plants, appreciably more leafage 

 and stem growth were produced on the noneroded than on the 

 eroded soil. 



Erosion is adverse to plant growth chiefly (i) because eroded 

 soils are so deficient in soil moisture as to prevent the full de- 

 velopment and seed production of the vegetation, and (2) be- 

 cause of the lack of adequate plant nutrients in the soil caused 

 by the leaching out of the soluble plant foods. Owing to the 

 deficiencies in the essential nutrients only certain inferior types 

 of vegetation can occupy eroded areas. 



Erosion and Revegetation. — The estabhshment on over- 

 grazed and eroding soils of a dense vegetative cover of the 

 more desirable forage and other deep-rooted, soil-binding spe- 

 cies is a most difficult task. The results of (i) the initial and 

 (2) the advanced stages of overgrazing in its relation to erosion, 

 and the attending economic consequences, are summarized in 

 Figure 62, and show the usual steps involved. Revegetation is 

 difficult, in the first place, because of the low moisture content 

 and lowered water-holding capacity of eroded soils; and, in the 

 second place, because of the fact that a large proportion of the 

 plants which do come up die early in the spring, often in the 

 seedling stage. The few that live through the spring usually 

 die before the end of the season. So serious is this loss of seed- 

 ling plants on eroded areas that it is often possible to predict 

 with much precision not only the rate with which the ground 

 cover may be restored but, as indicated in Figure 62, the par- 

 ticular kinds of plants which will occupy areas in different de- 

 grees of depletion. 



