MAINTAINING SOIL FERTILITY 289 



If the land is hilly and will probably wash 

 badly if cleared, the less of it that is* cleared, the 

 better. We rarely find bad gullies in woodlands, 

 even on the steepest hillsides; the roots of trees 

 hold the soil and the humus beneath them ab- 

 sorbs and holds the water, preventing it from 

 gathering in channels. Moreover, much of the 

 rainfall does not reach the soil, being intercepted 

 by the foliage and evaporated before it reaches the 

 ground. The direct force of the rain is also bro- 

 ken. It may be wiser to farm only the bottom land 

 and gentle slopes, and cultivate them more in- 

 tensely, than to clear uplands that are bound to 

 wash badly after most of the humus in them is 

 destroyed by cropping. 



If it is necessary to clear long slopes much may 

 be done to prevent serious loss from erosion by 

 alternating strips of forest with strips of tilled or 

 pasture land. The retaining strips of forest should 

 be twenty or more rods wide, depending upon the 

 steepness of the slope, and should run diagonally 

 across the slope or follow the contour of it. It is 

 especially necessary to keep the tops of hills in 

 forest, because there is where the water be- 

 gins to collect; moreover, the soil of hill-tops is 

 apt to be thinner and poorer than soil lower down 

 the slope. 



Slopes that have already been cleared and have 

 started to wash badly may have strips of woods 

 planted across them. In a surprisingly short 

 time trees will make an effective barrier to erosion. 

 It may be wise to give up an entire slope that is 

 washing badly to forest growth. Native trees 

 usually come in quickly, but if they do not seeds or 

 seedlings may be planted. 



Planting Trees to Prevent Erosion. When 



