THE CUBA R E \M E \V 



THE VALUE OF WINDBREAKS 



The influence and \alue of windbreaks 

 forms the subject treated in Bulletin No. 

 86, of the Forest Service, United States 

 Department of Agriculture. 



The term "windbreak" may be applied 

 to any object which serves as an obstacle 

 to surface winds, and may be divided ac- 

 cording to their general arrangement into 

 three classes: (1) Rows and hedgerows; 

 (2) belts or shelter belts; (3) groves, or, 

 in the most extensive case, forests. A 

 belt usually consists of three rows or 

 more, but its width is less than twice the 

 ultimate height of the trees. 



Orchards must be protected by wind- 

 breaks from the mechanical effects of the 

 winds which strike the trees when they are 

 laden wtih fruit ; from their drying effect, 

 which blights the fruit and causes it to 

 shrink ; and from the drying or "winter- 

 killing" of the branches. 



The ability of the windbreak to check 

 damaging evaporation must be its source 

 of greatest benefit, since, in the region 

 where windbreaks find their greatest use- 

 fulness moisture is almost always insuffi- 

 cient for the best interests of agriculture. 

 To thoroughly understand the influence 

 of a windbreak upon evaporation it 

 should be stated that the evaporation of 

 water from any wet surface and also the 

 transpiration of moisture from the leaves 

 of plants is accelerated by three conditions 

 — heat, dryness of the air and rapid air 

 circulation. Hence, anything which re- 

 duces the movement of the air reduces the 

 rate of evaporation and may effect an ap- 

 preciable saving of the moisture supply. 



While the windbreak affects evaporation 

 by checking the movemnt of the surface 

 air currents, it may also affect the tem- 

 perature of the air. 



A body of trees modifies the tempera- 

 ture of the air within it. In the daytime 

 direct insolation is prevented and the air 



SI 

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is cooler than it is outside. At night the 

 heat waves radiated from the ground are 

 intercepted and the air under the trees is 

 warmer than outside. Comparative uni- 

 formity of temperature is further secured 

 by the fact that the boles and branches 

 of the trees store certain quantities of 

 heat and that this heat is only very slowly 

 radiated. 



Windbreaks still the air, and the dis- 

 tances at which the calming effect may be 

 felt depends upon the depth of the mass 

 of air so calmed (which will, of course, 

 be equal to the height of the trees), and 

 also upon the mean velocity of the air in 

 the area of calm (determined by the leak- 

 age through the windbreak). Actually the 

 average distance was found to be not 

 more than twenty times the height of the 

 windbreak, and at that distance almost the 

 same velocities were experienced as were 

 found on the windward side of the wind- 

 break. Where the windbreak is of small 

 value or even exerts a positively injurious 

 influence is on land where the drainage is 



Windbreak of Eucalyptus Trees on :i California 

 Orange Grove 



BEST TOWN IN CUBA 



Postofifice, railroad, stores, church, school, saw- 

 mill, etc., good American neighbors; home and 

 fruit grove started, but v^^ish to devote all my at- 

 tention to other business. Will take northern 

 property on the deal — any way to please. 



Address "OWNER," care "The Cuban Review." 



