KESULTS OF MEASUREMENTS. 



49 



dense grove of cottonwoods, the belt of coniferous trees, the dense 

 hedge of osage orange, the mulberry hedge, the single row of cotton- 

 wood when growing with its greatest density and when reinforced with 

 ash are all to be classed as efficient windbreaks; the belt of cotton- 

 woods and the trimmed osage hedge maintained about the same mod- 

 erate efficiency to a velocity of 20 miles per hour; the single row of 

 honey locust, though as dense as possible for this species, and the 

 widely spaced row of cottonwoods show a decreasing efficiency with an 

 increase above 5 miles per hour, and can not be considered efficient. 



/o 



Of HE/GHT 



DIAGRAM 20. Protective efficiency of cottoiiwood row reinforced with ash. For wind velocities of 

 5, 10, 15, and 20 miles per hour. Height of cottonwood, 100 feet; ash, 45 feet, 5o readings. 



Considering that the zone of economically important protection is 

 between the point 2-ht. windward and the point 10-ht. leeward, the 

 average efficiency over this area, which in the case of a 50-foot wind- 

 break would be 600 feet wide, has been calculated on the basis of each 

 of the curves on diagrams 16 to 24, inclusive. The mean values are 

 given in Table 9. 



92290 Bull. 8611 -- 4 



