22 FORESTRY 



humidity of the atmosphere. Indeed, the impression con- 

 veyed by these statements was that whatever imperfection 

 the climate of the district possessed might be cured by the 

 establishment of forests. Thus the forest was supposed to 

 increase or diminish heat and cold, attract rain, or prevent 

 downpours and floodings as circumstances demanded! 



The more careful research and exact study of recent years 

 have, however, shown that the climatic influence of forests 

 is quite inconsiderable, and that neither afforestation nor 

 the destruction of forests has any appreciable effect. This 

 may, at least, be said of the British Isles and continental 

 lands in North-western Europe. 



The difference of the mean annual temperature without 

 and within the forest amounts to only about i Fahr. In 

 fact, it is occasionally less than the difference which arises 

 between two methods of observation. Perhaps the rainfall 

 over the forest is slightly greater than that in the open, but 

 though the finest tests have been made, even this has not as 

 yet been clearly demonstrated. On the other hand, owing to 

 the rapid evaporation of rain from the crowns of the trees, 

 considerably less water reaches the soil in woods than in 

 the open country. This is especially marked in countries 

 like Great Britain, where a considerable portion of the 

 annual precipitation is in the form of showers and mist. 



But the forest is not without its favourable effects by any 

 means. Apart from the fact that they add organic matter to 

 the soil, forests have a beneficial action in 



(1) Preventing direct sunlight from reaching the soil, 



a condition of things associated with certain 

 prejudicial influences. 



(2) Breaking the force of the wind. 



(3) Reducing the mechanical force of very heavy rain. 

 (4.) Binding soils apt to be carried away by flooding or 



drifting. 



In hilly country the prevention of erosion is, without 



