422 



FORESTRY AND IRRIGATION. 



October, 



the last 30 years, and it is now possible 

 to define the climate of that region with 

 a fair degree of accuracy. 



Climatic tables are presented herewith 

 for three points Duluth, in the extreme 

 western portion of the belt, and Mar- 

 quette and Alpena, Michigan those 

 points being considered as typical of the 

 climatic zone in which the White Pine 

 reaches its fullest development. 



The total annual precipitation of the 

 white pine belt averages from about 30 

 inches in eastern Minnesota to over 40 

 inches in the Canadian maritime prov- 

 inces. The greater part of the belt 

 within United States territory, however, 

 has an average of from 30 to 35 inches, 

 one-fourth of which is in the form of 

 snow. Snow falls in November and lies 

 on the ground, as a rule, until toward 

 the end of April. The average depth 

 varies greatly. On the upper peninsula 

 of Michigan and in the Georgian Bay 

 region 125 to 150 inches fall annually, 

 while on the southern edge of the belt 

 and at a somewhat greater distance from 

 large bodies of water the fall is not 

 much more than 50 inches. 



The distinguishing characteristics of 

 the precipitation of the white pine belt 

 are, uniformity of distribution through- 

 out the year and great frequency of 

 small rains. The frequency of small 

 rains or days with rain is best illustrated 

 by a comparison with points to the west- 

 ward. Thus the number of days with 

 rain or snow at Bismarck, North Dakota, 

 is on the average for the year 104 ; St. 

 Paul, Minnesota, 117; Duluth, Minne- 

 sota, 140; Marquette, Michigan, 158; 

 Alpena, 166. 



The Great I^akes and connecting 

 rivers within the white pine belt com- 

 prise within their borders about 100,000 

 square miles of water surface, an area 

 greater than that of New England, New 

 Jersey, Maryland, and Delaware com- 

 bined. This great body of water exer- 

 cises a marked control over the climate, 

 not only of the lake region itself, but of 

 the country far to the eastward. 



In a region devoid of vegetation or 

 forest covering, the soil radiates heat 

 very rapidly during the season of di- 

 minished solar activity, and becomes 

 intensely cold in the depths of winter. 



Likewise with the return of the sun 

 and the increased insolation of the sum- 

 mer season, the soil becomes very warm, 

 and these conditions of the soil extreme 

 heat in summer and cold in winter re- 

 act upon the superincumbent atmos- 

 phere and thus modify the climate. 

 The land surface of the white pine 

 belt is made up largely of areas from 

 which the timber has been removed, 

 but on which more or less underbrush 

 remains and alternating tracts of cleared 

 land and forest. Other things being 

 equal, there is not much difference be- 

 tween a forested area on the one hand 

 and a region of cultivated land on the 

 other, so far as permanency of climate 

 is concerned. It hardly seems probable 

 that any material change in the climate 

 of the white pine belt has taken place 

 as a result of the wholesale removal of 

 the timber. This belief is held for two 

 reasons : First, the deforested areas in 

 a number of cases have been recovered 

 by a second growth of timber or by 

 underbrush, thus preserving in a cer- 

 tain degree the character of the original 

 covering. Second, suppose no timber 

 whatever had been removed from the 

 original stand ; the only influence on 

 climate that could properly be ascribed 

 to the original forest cover would be 

 increased evaporation and a very slight 

 modification in the temperature. The 

 increased moisture given off by the trees 

 would rise in the air and be carried 

 eastward by the prevailing westerl}^ 

 winds, so that the rainfall of the for- 

 ested areas would not be increased b}^ 

 an appreciable amount, but there might 

 be a small increase to the eastward 



If the whole continent had mostly a 

 hard and barren surface, the interior 

 would be intensely cold in winter and 

 hot in summer. The rainfall would be 

 carried off rapidly, and evaporation 

 would be diminished over the conti- 

 nent, while there would be no increase 

 over the ocean. The net result of such 

 a change in surface conditions would 

 be a small diminution of rainfall on the 

 globe. As it is impossible through 

 human agencies to change the surface 

 conditions, except over extremely small 

 areas, it will at once be seen that all 

 apprehensions of permanent change of 



