20 THE ROLE OF FORESTS 



early French investigations. The results of an experiment (1869-1888) 

 in a beech forest at an altitude of 1,115 feet showed the mean annual tem- 

 perature inside the forest to be 0.45 C. less than outside. In thirteen 

 experiments at various altitudes in pine, spruce, beech, and larch forests, 

 the forest temperature averaged 0.66 C. less than in the open. The 

 difference was greater in summer than in winter. The mean maximum 

 days at Nancy averaged 24 0.48' C. (76 F.) in the open and 21 0.51' C. 

 (70 0.7'F.) in the forest. In the cold weather the average outside the 

 forest was -5 0.12' C. (31.89 F.), inside -4 0.24' C. (31.91 F.). The 

 investigation thus showed that the temperature extremes were raised 3 

 to 5 C. by a forest cover, but that the temperature in the forest was 

 warmer in winter and cooler in summer. In other words, the forest acts 

 as an equalizer of temperature. 6 



The Nancy research officers established the following laws: (1) The 

 mean annual temperature that was reached is | C. less in the forest than 

 in a nearby open area. (2) This difference in temperature, while slight 

 during the winter months, is greater in summer. (3) The minimum 

 temperature is raised in the forests by nearly 1 C. and the maximum 

 lessened about 2 C. In other words, there is a decided difference be- 

 tween the minimum and maximum of 3 C. 



In addition it may be said that conifers lessen winter extremes of tem- 

 perature more than do broadleaves and that the denser the summer 

 foliage the cooler the forest in comparison with the open areas. These 

 differences are greatest at 35 to 40 feet above the soil. 



Investigations by Cuif 7 show conclusively that soil is almost 4 C. 

 warmer during July in the open than under high forest or under coppice. 

 He also proved that soil temperature variations outside and inside the 

 forests are less extreme than the variations in the air temperature by from 

 2 to 4 C. 



Wind. The value of forests as shelter belts against the wind is 

 proved for agricultural crops and for water surfaces to prevent evapora- 

 tion. 



Frost. It has always been recognized that forest cover prevents 

 frosts. They are less frequent and less severe under cover, which is the 

 reason why the shelterwood system must be applied to beech. Without 

 the top story the beech seedlings would be frost-killed. In 1912 Cuif 8 

 proved that the forest cover prevented damage from late frosts and 

 showed that in the State forest of Amance (Meurthe-et-Moselle) oak 



Huffel, Vol. I, pp. 45-67. 



7 Influence du Couvert de la For6t sur la Temperature du sol a diverses profondeurs, 

 par M. E. Cuif. Bulletin de la Societe des Sciences, 1909. 



* Action de la Foret sur les Gelees Tardives, par M. E. Cuif. Annales de la Science 

 Agronomique francaise et etrangere. Sept., 1912. 



