32 



WINDBREAKS. 



narrow crowned and light foliaged. Maple has a narrow crown. 

 Green ash is to be recommended. Conifers, especially Scotch and 

 Austrian pine, white pine, and white cedar, which have narrow, conical 

 crowns, are very desirable. 



(3) The outer rows of a belt may consist of slower-growing "tol- 

 erant" trees which, unless they are of exceedingly slow growth, can 

 be planted after the main body of trees has attained a good height. 

 Spruce, fir, maple, and ash are good examples. Even osage orange 

 will grow in considerable shade. 



(4) The ground under the branches of tall trees may well be used 

 for roads. Secondary roads, used only in summer, should be on the 

 north and east sides of windbreaks. 



DIAGRAM 13. Yield of corn wost of various tree spreu-.--. K\t. :--! in percentages of yield at three 



times height. 



(5) In the Middle West, where most of the winds are southerly 

 or northerly, the east-west orientation should be established wherever 

 possible. In the northern prairies and Lake States the north-south 

 orientation will be found most useful. 



While the damage to crops may be greater from a dense and wide- 

 crowned species, such as osage orange, the protective value of the 

 windbreak may be greatly enhanced by such a crown. That the 

 protective value of a species is not necessarily proportional to its 

 shading power, however, is brought out later under the subject of 

 evaporation (p. 45) in the discussion of windbreak efficiency. 



