WINDBREAKS 241 



Protected orchards yielded from five to ten times the fruit that was borne 

 by exposed orchards, the damage to the fruit crop having been caused by 

 a cold northwest wind in April accompanied by precipitation. The distribu- 

 tion of the fruit on the trees and through the orchards proved that the April 

 storm from the northwest was responsible for the killing of the fruit buds 

 and for the small crop of apples where windbreaks were not present. Wind 

 accompanied by precipitation is very trying to vegetation because the rapid 

 evaporation of the moisture on the leaves and branches consumes heat in 

 large quantities and depresses the temperature of the plants to a harmful 

 extent. 



The curves and tables refering to temperature would seem to indicate 

 that the heating and cooling effects of windbreaks practically balance each 

 other except in the area occupied by the trees. The investigations did not 

 take cognizance of the times either at night or in the winter when the normal 

 temperatures of the air fall below the soil temperatures. At such times, the 

 reduction of wind movement in the protected zone would cause the air tem- 

 peratures to rise because of radiated heat coming from the soil, hence the 

 effect of the windbreak would be to cause heat to accumulate in the air of 

 the protected area. This effect would be to prevent frosts rather than pro- 

 mote them. 



THE FINANCIAL BENEFITS 



In measurements of the direct financial results and timber yields, this 

 bulletin presents the first effort on the part of an investigator to ascertain 

 the damaging effects of windbreaks outside of the area belonging to the trees, 

 and to charge the plantation with the occupation and use of the land so 

 damaged. For instance, an Osage orange hedge a mile long oriented north 

 and south and 31 years old is charged with the use of 3.54 acres of land in 

 Table 23. In some of the earlier publications of the Forest Service, single 

 rows of trees were considered as not occupying any space, and the acreage 

 of blocks and belts was computed from measurements from outside row to 

 outside row. In small groves and narrow belts the error from such measure 

 ments often exceeded two hundred per cent. It is gratifying to note that 

 the Service has at last worked out accurate and scientific methods for 

 obtaining the value and yield of small farmers' plantations. 



The acreage occupied by single rows one mile long was computed by the 

 formula, A= - 4353 5 Q - where A represents acreage, CF the factor of 



damage to corn in percentage of height of trees, H the height of the trees, and 

 the factor 3-5 is assumed to be the average damage during the whole life of the 

 trees, it being conceded that the damage during the early growth of the plan- 

 tations was very much less than their present measured damage. The formula 

 can be used for single rows of any length provided the actual length in feet is 

 substituted for the number 5280. If the acreage occupied by a belt a mile 



