uses, sometimes resorted to, are the protection of irrigation ditches and high- 

 ways from drifting soils. 



Range of Effectiveness. The extent and degree of the effectiveness of a 

 windbreak depend upon its density, height, and location. Where air passes 

 through, as often occurs in single rows of trees, its velocity is diminished, 

 but not effectively checked. A dense growth, of equal height, protects a 

 large area and is of much greater value. The distance over which an effective 

 windbreak exerts a beneficial influence has, from several statements of others, 

 been found to be approximately ten times as great as the height of the trees. 

 Location should be influenced by height of the trees and direction of the wind 

 from which the buildings or fields are to receive protection. Prevailing winds 

 are from the southwest, a fact which renders planting necessary on the south 

 and west of buildings and fields. 



Location is a difficult problem in this region, as the course of prevailing 

 winds is diagonal to farm boundaries. The land is rolling and irregular in 

 character. 



Best results appear to accrue from planting on the south and west lines 

 of each 10- or 20-acreunit. Hot, drying, summer winds of infrequent occurrence 

 from the northeast are not of sufficient consequence on irrigated land to 

 justify the establishment of windbreaks. 



Assuming that the beneficial influence of a windbreak extends over a 

 distance ten times its height, as cited above, the distance between windbreaks 

 on each farm unit will depend upon the height of the trees used and the slope 

 of the land. Plans should be made accordingly in selecting trees and locating 

 windbreaks. 



Formation of Frost Pockets. Windbreaks of tall growing trees should not 

 be located so as to interfere with air drainage. Such barriers to air movement 

 become a strong factor in creating local frost areas. It is by hindering the 

 movement of cold, heavy air from high to low elevations that such areas or 

 pockets are formed. To avoid this, open spaces through windbreaks should 

 be left in depressions and on the lower sides of partly inclosed fields. Air 

 drainage is similar to the removal of surplus water from the surface of the 

 land. The cold, heavy air should be allowed to escape in a similar manner 

 from the lowest portions of the fields. 



Plants to Use for Windbreaks. Since it is practically impossible to get a 

 tree with all the requirements for an effective windbreak, the best shelter 

 can be developed by combining several species. 



Deciduous trees are desirable for establishing windbreaks on new land, 

 as they grow much more rapidly than conifers. They are also much cheaper 

 and more easily started than evergreens. Although a few damaging winds 

 sometimes occur in the spring before they leaf out, their value for the entire 

 season is not materially lessened by the temporary absence of leaves. 



Poplars are frequently < chosen in preference to black locust, since they 

 come into leaf earlier and are less subject to injury from frost. 



With proper care, rapid-growing trees become of considerable value in 

 three to five years. Black locust and Lombardy poplar range from 15 to 25 



