SIZE OF EFFICIENT WINDBREAKS. 



93 



, they were cut. If, however, the aggregate benefit up to the time of 

 i cutting is calculated, there is in favor of the hedge a considerable 



surplus which may be used to tide over the few years before the 



sprouts again become efficient. 



Table 26, on which the calculations of benefit are based, shows the 



height growth on moderately moist to dry situations. 



TABLE 26. Height growth of osage hedges. 



Calculating the value of an osage hedge on the basis of an annual 

 net benefit equal to the yield of a strip of ground twice as wide as the 

 height of the trees, there is at the end of 20 years a surplus in favor 

 of the windbreak on B class situation, of $1,980. This is sufficient 

 to pay for the total loss of crop in the area occupied by the old roots, 

 68 feet wide, for 12 years after the cutting. As a matter of fact, the 

 height growth of osage coppice is so rapid that in a very few years 

 the hedge will again be paying for itself. 



The single-row hedge or windbreak must be primarily for the pro- 

 duction of posts and small timbers in which freedom from knots is 

 not an essential feature. Protection and high quality timber pro- 

 tion can be secured only in the wide windbreak, where forest 



editions are obtained, and where the body of the trees, as a whole, 

 forms a barrier to the wind. 



The previous discussion has been based on the idea that the most 

 efficient protection is desirable, as for grain crops, for the protection 

 of houses and cattle sheds, and for the purposes of a snow trap. 

 There are situations, however, where a dense windbreak is not desira- 

 ble, and where the complete stagnation of the air would be injurious. 

 Orchards may sometimes be rendered colder, in the case of a frost on 

 a clear and relatively calm night, and again the danger from fungous 

 diseases is greater in the more humid air behind a windbreak than in 

 the open where the surfaces of leaves and fruit are kept dry by the 

 wind. These fungi are sometimes injurious to grain crops as well as 

 to fruits, and the damage arises during a period of wet weather. 

 The "rust" of wheat and "smut" of oats are of this character. It is 

 reasonable to suppose that the presence of a windbreak favors the 

 growth of these fungi. 



