3 i4 THE POPULAR SCIENCE MONTHLY 



based our own belief on any such evidence as the foregoing, we ought to 

 remember that our own sensation of heat, or cold, or dampness, by no 

 means necessarily, or even usually, corresponds with the actual meteoro- 

 logical facts. Further, the great rainy and dry belts of the earth's sur- 

 face are controlled by a world-wide distribution of temperature, pres- 

 sure and winds, that is, by the general circulation of the atmosphere, 

 and by conditions of the higher strata far and away beyond the reach 

 of any local effects such as those of a forest. Universally, in response to 

 natural controls, a scanty rainfall is hostile to tree-growth, and forests 

 are favored by heavy rainfall, which gives good conditions of soil-mois- 

 ture and is generally accompanied by higher relative humidity, more 

 cloudiness and less extreme temperatures than prevail over treeless re- 

 gions. In the case of mountains, again, it should be clearly in our 

 minds that, as a rule, and up to a certain limit, an increase of altitude 

 involves an increase of precipitation, quite apart from the presence or 

 absence of any forest. We must be careful not to put the cart before 

 the horse. The forests, in other words, are the result of the rainfall, 

 and not vice versa. 



Importance of the Subject : its Complexity 



That this subject has an important relation to our national conserva- 

 tion policy no one will deny. Unfortunately, the discussion of it has 

 become more or less a matter of semi-political controversy. Much has 

 been written without adequate study of the question. Heated argu- 

 ments, pro and con, have been advanced in debates and in print. Re- 

 markably divergent views have been, and are to-day, held upon the 

 question. It has been claimed that forests have no climatic influences 

 whatever. On the other hand, some have believed that deforestation in 

 North America has affected the climate of Europe. A recent writer 

 maintains that the principal cause of the "intellectual and industrial 

 stagnation " of the Spanish peasants is to be found in the effects of de- 

 forestation in making the climate drier, so that the people are " worked 

 to death to support life." The literature is extended and bewildering. 

 It runs back at least five hundred years. A bibliography published in 

 1872 contains nearly two hundred titles, and began with Fernando Co- 

 lumbus, who attributed the heavy rainfall of Jamaica to its heavy for- 

 ests, and a (supposed) decrease of rainfall on the Azores and Canaries 

 to deforestation. It has been said that this whole discussion first came 

 up in really acute form at the time of the French Revolution, when 

 private timberlands were largely destroyed. 



The subject is thus greatly complicated by the nature of the discus- 

 sion. It is, furthermore, by its very nature a complicated problem. On 

 the one hand, climate itself is the complex resultant of many different 

 controls. Among these are the latitude; the elevation above sea-level; 

 the varying influences of land and water; the proximity of ocean cur- 

 rents ; the prevailing winds and storms. In this list of controls, but at 



