68 WINDBREAKS. 



EFFECT OF LOW TEMPERATURES. 



The lowering of the minimum temperature, and probably also of the 

 mean temperature at night, would partly tend to offset the beneficial 

 superheating in the shelter of the windbreak during the day, especially 

 with such crops as corn, which, when the temperature is propitious, 

 are said to grow as much at night as in the daytime. Diagram 30 

 shows that the effect of the plants themselves in stagnating the air 

 in a field of mature corn is almost great enough to obliterate the 

 influence of the windbreak on the temperature at 4 feet from the 

 ground, the point at which records were made. On the windward 

 side a uniform temperature more than 1 degree lower than the normal 

 prevailed, while on the leeward* side, during a rain, all the tempera- 

 tures were so much lower as to make the curve appear negative. 

 That positive benefit resulted here, however, is shown by the direction 

 of the curve as it leaves the windbreak, the lowest temperature being 

 at the farthest point where the wind again gained force. But under 

 any circumstances the activity of most plants is very much lessened 

 at night by the absence of sunlight, and the few degrees difference in 

 temperature would have very little effect on most cereals, especially 

 upon wheat, which grows thriftily at the time of the year when the 

 usual night temperature is below freezing. The influence of this 

 depression of the minimum can not, however, be overlooked in the 

 case of orchards, since fruit trees are very susceptible to the least frost, 

 especially at the time of blossoming. A lowering of 4 or 5 degrees in 

 the minimum temperature might mean the difference between a mere 

 chilling of the tender fruit blossoms and actual freezing. On this 

 account orchardists are usually of the opinion that a windbreak is 

 quite as likely to bring damage as benefit to fruit crops. Damage 

 from slight, dry freezing, however, is not apt to lead to a complete 

 loss of the fruit crop, such as occurs when the blossoming trees are 

 subjected to a storm of rain, sleet, or snow accompanied by wind. 



The Middle Western States during the season of 1908 furnished a 

 striking example of damage to unprotected orchards. The possibil- 

 ity of a crop in a very large number of unprotected apple orchards 

 was destroyed and the crop in but poorly protected orchards was 

 greatly reduced. 



Near David City, Nebr., where the results of the storms at the 

 end of April and the beginning of May were perhaps most severe, 

 there was early promise of an unusually good fruit crop, following 

 a very poor season in 1907. The storm which did the most damage 

 to blossoming fruit trees came from the northwest on the night of 

 April 27, when a wind of about 10 miles an hour was blowing, a 

 small amount of rain and snow fell, and a minimum temperature 

 of 28 degrees was registered at the weather station. At the time 

 there was very little foliage either on the fruit trees or on the forest 



