66 



WINDBREAKS. 



From this point outward the gain diminished, and at 10-ht. it 

 amounted to about 6 bushels per acre. The net gain for the entire 

 area out to 10-ht., including the strip damaged by shading, and cal- 

 culating for a windbreak 1 mile long, was 423.86 bushels, or 9.22 

 bushels per acre; that is, as much corn as could be grown on an area 

 as long as the windbreak and as wide as twice the height of the 

 trees. The grove in question was wider than this, but need not 

 have been in order to have furnished almost equal protection. It 

 will, therefore, be seen that the benefit to corn, in this case, paid for 

 all of the ground needed for an efficient windbreak, so that the tim- 

 ber value of the trees was a clear gain to the farmer. 



In many other cases the benefit was equally marked on the north 

 side of windbreaks, as shown in Table 13. The gain in bushels has 

 been figured to show the width of strip for which the benefit pays 

 (above all damage from shading). The benefit is about proportional 

 to the density of the windbreak, and the point of greatest benefit 

 corresponds to the crests of heat and evaporation curves. In the 

 case of the dense grove, the crest is very near the trees and just 

 beyond the shading zone. 



TABLE 13. Showing benefit to corn arising from protection afforded by windbreaks 



North side. 



Similar but not so great benefit was measured on the south side 

 of four osage-orange hedges. Other measurements on the south side 

 are lacking, but it is safe to assume that the benefit would be propor- 

 tionately greater with denser windbreaks. The average of the cases 

 mentioned showed a maximum benefit of 12.11 bushels per acre at 

 1.99-ht. from the trees, which were 20 feet in height. The net 

 increase out to 10-ht. is equal to the yield of a strip 0.8821 times 

 as wide as the height of the trees. It will, therefore, be seen that 

 the osage-orange hedge, by the benefit on both sides, has brought a 

 net increase in corn yield equal to the yield of a strip 1.9074 times as 

 wide as the height of the trees, in addition to the value of the tim- 

 ber produced. With an osage hedge one-half mile long and 25 feet 

 high, and with corn at 45 bushels per acre and 50 cents per bushel, 

 the increased revenue from the corn would be $65.05. 



