PLANT INDUSTRIES 327 



with increased rapidity. In so doing it carries away large 

 quantities of soil, sometimes uncovering the burned roots 

 until the trees are easily overturned by winds. 1 



There are several means of preventing much of this loss of 

 soil by erosion. In wooded regions judiciously cutting part of 

 the timber each year, rather than cutting all of it at once, 

 gives opportunity for new plants to occupy and hold the soil. 

 There are many kinds of soil-holding plants which, if properly 

 placed, will prevent erosion in its earliest stages, and these 

 should be used. In open, hilly fields which are exposed to ero- 

 sion, grass and meadow crops are desirable, since their roots 

 help to hold the soil throughout the whole year. In such 

 cases the roots and stems help to prevent the rapid run-off 

 of the surface water. The very things that need to be done 

 in the cultivation of plants increase the danger of loss of soil 

 where rapid flow of the surface water cannot be prevented. 



In hilly fields it is often difficult, sometimes impossible, to 

 prevent erosion. In some localities the rows of growing plants 

 are arranged across the slope of the hill; this arrangement 

 helps somewhat in retarding the surface flow of water. If culti- 

 vation is continued in such places, the soil sooner or later be- 

 comes eroded, and it is with extreme difficulty that any plants 

 gain a foothold (fig. 240). In some foreign countries hillsides 

 have been saved for cultivation by a process of terracing. 

 The terraces are constructed in such a way that the soil upon 

 each is level or slopes toward the hill, thus retarding or pre- 

 venting erosion. Such terraced farms are sometimes most desir- 

 able for vineyards, but it is obvious that for ordinary crops these 

 elaborate processes of terracing, and the constant care required, 

 will prove profitable only where available land is extremely 

 scarce. In many localities where the slope of the surface is 

 moderate enough, underground drains may be laid to take care 

 of the surface flow and thus prevent erosion except at times of 

 extremely heavy rains. 



1 ft The Movement of Soil Material by the Wind," Bulletin 68, Bureau of 

 Soils, U.S. Dept. Agr., 1911. 



