PART IV. 



SUMMARY. 

 CALCULATION OF THE SIZE OF EFFICIENT WINDBREAKS. 



The protective value of an osage-orange hedge in the season of 

 1908 was equal to the yield of a strip twice as wide as the height of 

 the trees. The protection afforded by the most efficient grove wind- 

 breaks amounted to the yield of a strip three times as wide as the 

 height of the trees. This means that the farmer in the Middle West 

 can afford to maintain a windbreak running through the farm from 

 east to west, and having a width of 240 feet in the case of mature 

 cottonwoods 80 feet high. On a farm of 160 acres this would give 

 approximately 15 acres of timber, or about 10 per cent of the area. 

 There should be at least two such strips, however, to protect the entire 

 farm from both north and south winds. This is the recommendation 

 made by European agricultural economists, that 20 per cent of the 

 farm should be in forests. Such windbreaks as these, by protection 

 alone, will pay a rental on the ground which they occupy equal to 

 that from grain crops. 



In addition to the protection it has been shown that windbreaks of 

 nearly every species planted in the Middle West have a high timber 

 value at maturity. 



SIZE OF EFFICIENT WINDBREAKS DETERMINED BY THEIR 



VALUES. 



GROVES AND SHELTER BELTS. 



The figures which represent the protective value of windbreaks 

 apply only after the windbreaks, or more properly the trees within 

 them, have become mature, and do not take into account the fact 

 that the protective value of a belt of young trees is much less in pro- 

 portion to its width than the protection afforded when the trees 

 have attained their full height. In most cases it would not be practi- 

 cable to gradually increase the width of the windbreak as the trees 

 become taller, and it is, generally speaking, more profitable from the 

 lumberman's standpoint to make a clean cutting when the timber is 

 harvested; it is, therefore, necessary to calculate the total protec- 

 tive value of the windbreak from the time of planting to maturity, 

 and to balance this against the total value of crops which might have 

 been grown on the land occupied by the trees during the same period. 



Roughly, the average protection given by the belt of trees is one- 

 half as great as that given at maturity, since it increases directly 

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