THE WINDBREAK AS A FARM ASSET. 13 



the easterly winds which usually precede and accompany a storm. 

 White pine is recommended above all other species, because of its 

 rapid growth and high timber value, which justify its planting in 

 wide belts or groves. The planting of white cedar along the edges 

 of older white-pine belts will greatly increase the efficiency of the 

 existing windbreak. On the poorer soils Norway or Scotch pines 

 may be used instead of white pine. 



In the Eastern States the situation is essentially the same as in 

 the Lake States. White pine may be generally used, and white and 

 Norway spruces and white cedar may be used in mixture or to 

 strengthen the older windbreak on the sides. 



In the Southwest the choice of species is very limited, and in typi- 

 cally dry situations possibly nothing can be made to succeed which 

 has greater value than sagebrush in the form of hedges placed at 

 frequent intervals. With a little more moisture the native ever- 

 greens, pifion, alligator juniper, and cedars may be made to grow. 

 With irrigation the species used in the Middle West can undoubtedly 

 be utilized to good advantage. If possible, the windbreaks should 

 extend northwest-southeast. 



In California citrus orchards and other valuable crops need pro- 

 tection on all sides. Protection from the northerly " Santa Ana " 

 is probably most essential to grains and other field crops. For all of 

 these purposes Monterey cypress, Monterey pine, and eucalypts have 

 proved very valuable. 



In the Columbia River region of the Northwest, Carolina and 

 Loinbardy poplars and cottonwood are very efficient for the protec- 

 tion of orchards and crops against the mountain winds, usually of 

 easterly origin. Even small willows have been used to good advan- 

 tage in checking the drifting of sand. 



GROUND SPACE NECESSARY. 



The belt of trees forming a windbreak needs the use of a certain 

 amount of ground beyond that on which it actually stands. There 

 must be space for the roots to spread out in search of soil nourish- 

 ment and moisture. It should be remembered that the row of trees 

 is a productive agent quite as much as a row of corn and may need 

 just as much growing space in proportion to its height. Some spe- 

 cies of trees, of course, spread their roots wider than others and 

 need more space. Of those commonly planted, mulberry, honey 

 locust, and osage orange spread the farthest in proportion to their 

 height, and green ash spreads the least. Cottonwood does not spread 

 its roots so far as is generally supposed. 



Cultivation tends to limit the spread of the roots by making more 

 moisture available near the trees, though deep plowing or cutting 

 the roots restricts the root extension at the expense of the growth 



