abstracts: forestry 93 



twenty times its height, altho absolute protection of a crop such as 

 corn, in a -wind with a velocity of 50 miles an hour, can not be expected 

 beyond a distance of from six to eight times the height of the wind- 

 break. Partial protection is given over a distance of from twelve to 

 fourteen times the height. 



The efficiency of a windbreak in checking evaporation from the soil 

 may, in extreme cases, amount to 70 per cent of the moisture ordinarily 

 lost. Protection in this respect is appreciable for a distance equal to 

 five times the height of the trees in the windward direction, and fifteen 

 or twenty times the height leeward. 



The effect of a windbreak upon temperature in the zone of its influence 

 is much greater than is commonly supposed. The daily range of tem- 

 perature in an area protected by a windbreak is nearly 9° F. greater than 

 where the air circulates freely. The effect of the superheating of both 

 air and soil in a protected zone is favorable to crops which must begin 

 growth at a time when the beat is barely sufficient for germination. 

 Corn and alfalfa are the field crops least affected by the shade from wind- 

 breaks. 



Honey locust and osage orange are the trees adapted to windbreak 

 planting which cast the heaviest shade. Cottonwood, maple, green 

 ash, white cedar, and Scotch, Austrian, and white pine are those which 

 cast the least. 



The absorption of soil moisture by the roots in a windbreak may in the 

 case of an orchard be appreciable, but need not result in real damage. 

 Corn, oats, and wheat may suffer within 45 feet from the windbreak, but 

 with care the effect is much less apparent. It may be greatly lessened 

 by thorough cultivation of the soil near the trees, by planting tap rooted 

 species in the windbreak, or by the use of seed crops next to the trees. 

 There is little basis for the belief that windbreaks sap the fertility of 

 the soil. The trees' use of soil moisture may, however, reduce the 

 activity of the nitrifying bacteria and cause temporary sterility in the 

 zone of root influence. 



Cottonwood is the best tree for windbreaks in the middle west; 

 Scotch pine, Norway pine, and Colorado blue spruce in the northern 

 prairies; white pine in the lake and northeastern States; chestnut and 

 yellow poplar m the central eastern States ; osage orange in the southwest; 

 eucalypts, Monterey cypress and Monterey pine in California; and pop- 

 lars, willows, and cottonwoods in Washington and Oregon. 



Findley Burns. 



