1885.] METEOROLOGY. 183 



Meteorology. 



THE INFLUENCE OF FORESTS ON CLIMATE. 



THE third number of retermann's Mitihcilunycn for this year 

 contains an article by Herr A. Woeikof on the influence of 

 forests on climate. The commencement of a scientific investigation 

 of this subject was made when the Bavarian forest meteorological 

 stations were established, and when Prussia, Alsace-Lorraine, 

 France, Switzerland, and Italy followed the example. As a 

 general rule, it may be laid down that in the warm seasons, as 

 between forests and places close at hand which are treeless, (1) 

 the temperatures of the earth and air are lower in the former, 

 (2) their variations are less, (3) the relative humidity is greater. 

 After examining observations as to evaporations, Herr Woeikof 

 states that the influence of forests in diminishing evaporation from 

 water and the soil is so great that it cannot be accounted for alone 

 by the lower temperature of the hot months, the greater humidity, 

 or even by the shade. An important influence, which has hitherto 

 been but little appreciated, is the protection from the wind afforded 

 by the trees, and this the writer regards as more important than 

 all the others together in reducing the degree of evaporation. With 

 regard to the influence of forests on rain and snowfall, there is as 

 yet only a single series of observations supplying comparative 

 statistics, and extending over a sufficiently long period. These 

 were taken in the neighbourhood of Nancy, and they show an 

 important influence of forests in increasing the rainfall. It might 

 appear that the effect of forests on rain in the climate of Central 

 Europe in winter would be small, for the difference between the 

 temperature and humidity of the forest and the open is very little, 

 and the quantity of moisture in the atmosphere is small. But the 

 observations show that it is at this time of the year that forests 

 get much more rain. This the writer attributes to the clouds being 

 lower, the resistance which the forest offers to the movement of 

 the air, and to the moist west wind. Forests retain rain by the 

 undergrowths of grass, moss, etc., much better than open ground, 

 and let water off superficially only after a heavy rainfall; the 

 remainder filters upwards slowly, and much of it is used for the 

 evaporation by the trees. Although forests, especially thick, 

 luxuriant forests, cannot exist without certain supplies of mois- 

 ture, yet it is the same to them when the supplies come, for they 

 retain what they get and use it over a long period. One example 



