DIVISION OF FORESTRY. 153 



(4) The total atmospheric precipitation is not necessarily diminished, 

 unless clearing has been made over very extensive regions, but the 

 distribution throughout the year will be disturbed; the amount, how- 

 ever, which reaches the soil is largely increased. 



(b) On the climate of the surrounding country. 



(1) The areas that were situated near the forest lose their protec- 

 tion against drying and cold winds. 



(2) The force of the winds is unbroken; a change more detrimental 

 where the configuration of the ground does not fulfill a similar func- 

 tion, in large j^lains more tlian in hilly and mountainous regions, and 

 at the sea coast more than in the interior. 



(3) The unfavorable consequences of deforestation are more marked 

 the more the climate of a locality has a continental character, and the 

 less marked the more it approaches Ihe character of a coast-climate.* 



B. — Effects of deforestation on water supply. 



(1) After deforestation the soil is deprived of very much less water 

 by the process of vegetation than before. 



(2) Where a superfiuity of moisture used to be removed by this proc- 

 ess, deforestation often induces a formation of marshes, and, in con- 

 sequence, unfavorable sanitary infl.uences on the surroundings are 

 possible. 



(3) In consequence of deforestation, evaporation from the soil is 

 augmented a:nd accelerated, resulting in an unfavorable infl.uence on 

 soil humidity and on the size and continuity of springs. 



(4) With the disappearance of the forest the retarding influence of 

 soil cover and of trunks on the superficial flow of water ceases. 



(5) This circumstance, in conjunction with the augmented evapo- 

 ration from the superficial springs and rivulets and from the soil, 

 causes the unfavorable influence of deforestation on the flow of brooks 

 and rivers. 



* From this it will at once appear how futile must be the attempts to name a cer- 

 tain percentage of forest cover as necessary for a country to preserve favorable 

 climatic and hydrologic conditions, and another percentage for the requirements of 

 raw material. As the latter must depend upon the number of inhabitants, the pro- 

 ductiveness of the forest, and several other variable factors, so does the former de- 

 f)end on conditions the bearing of each of which we have not yet been able to calcu- 

 ate ; it must certainly vary according to geograpliical location and configuration of 

 soil. England, with its moist and cloudy climate, in a temperate zone, can well 

 dispense with a large per centage of forest cover — it has only 3.23 per cent. — while 

 poor thirsty Spain suffers from drought with 18.30 per cent, of forest, and Austria, 

 on account of the configuration and character of her territory and the great number 

 of water-sheds, feels the need of more than 30 per cent, of forest cover. For a coun- 

 try like the United States it is impossible to pronounce upon a required forest area 

 for climatic reasons, as its parts must so widely differ in this, that no meaning could 

 be attached to any percentage expressed for the total. (See table on page 185.) From 

 the table on page 169, on which the percentage of forest cover, in different sections is 

 noted, it will appear that, if the forest areas exist as reported, it can hardly be said 

 that the percentage of forest is dangerously out of proportion on the Atlantic coast, 

 the Gulf States, or even the Central and the lake-surrounding Northern lumbering 

 States; on the other hand, the Vv^esternagricultui-al, prairie, and mountain regions 

 appear decidedly deficient. While, therefore, local hardships, due to injudicious 

 clearing of hillsides, may be brought about in the first-mentioned sections, the 

 climatic aspect of the forestry problem concerns most nearly and immediately the 

 central and western half of the country, where a continental climate and the inter- 

 ference of high mountain ranges with moisture-laden winds, call most strongly for 

 the modifying influence of the forest. 



