FORESTS AND THEIR CLIMATIC INFLUENCE. 



By M. Becquerel, Member of the French Institute. 



[Translated for the Smithsouiau Institution.*] 

 FORESTS CONSIDERED IN A CLIMATOLOGICAL POrNT OF VIEW. 



Forests exercise several kinds of iuflnence over climate ; but, to appre- 

 ciate them properly, it is necessary to define what we understand by 

 climate. 



The climate of a country, according to Humboldt, is the union of the 

 phenomena, whether calorific, aqueous, luminous, aerial, electrical, &c., 

 which impress on that country a definite meteorological character, dif- 

 ferent from that of another country situated under the same latitude 

 and placed in the same geological conditions. Accordingly as one of 

 these phenomena predominates, the climate is said to be warm, cold, or 

 temperate, dry or humid, calm or variable. Heat, however, is regarded 

 as exerting the greatest influence ; after this follow the quantities of 

 water which fall in different seasons of the year, the humidity or dry- 

 ness of the air, the ijrevailiug winds, the number and distribution of 

 storms in the course of the year ; the serenity or nebulosity of the air ; 

 the nature of the soil and that of the vegetation which covers it, accord- 

 ingly as this is spontaneous or the result of culture. 



1. What is the part which forests fulfill as a shelter against the winds 

 or in retarding the evaporation of the rain-water"? 2. What is the 

 influence of trees on the water imbibed by the roots and on that which 

 exudes by the leaves, as modifying the hygrometric state of the ambient 

 air ? 3. How do they modify the calorific state of a country ? 4. Do 

 forests exert an influence on the quantity of water which falls, and on 

 the distribution of rains in the course of the year, as well as on the 

 system of runuing waters and those of springs ? 5. How do they inter- 

 vene for the preservation of mountains and of slopes ? G. Do forests 

 serve to withdraw from storm-clouds their electri<*ity, and thus to mod- 

 erate their effect on neighboring and unwooded regions '? 7. What is 

 the nature of the influence which they are capable of exerting as regards 

 the public health ? 



From this series of questions it will be seen how much caution is to 

 be observed before we pronounce on the influence which the disboscation 

 or clearing awa^^ of the forests of a country may exert on its climate. 

 It is necessary, first, to know the geographical position, the geological 

 constitution of that country, its latitud.e, its proximity to or remoteness 

 from the sea, the nature of its soil and that of its subsoil, according as 

 one or the other is permeable or impermeable, siliceous, calcareous, or 

 argillaceous — elements which must all be taken into consideration. 

 These questions, with the exception of a few, not being susceptible of 

 solution a priori, exact, of course, a special examination and experi- 

 mental study, without which we incur the risk of pronouncing an opin- 

 ion not in accordance with that of one who may have considered the 



* From the Atlas Meteorologique de V Obscrvatolre Imperial. Folio, Paris, 1867. 



