326 M. BECQUEREL, ON THE CLIMATIC EFFECTS OF FOEESTS. 



that results has a cooling effect upon the climate ; while dryness or 

 aridity produce the contrary effect. 



It will be found, however, that if the mean temperature remains the 

 same, the distribution of heat through the year would change, and that 

 thus the climate would be modified. On the other hand, we cannot 

 appeal to documents relating to cultivation, which will not bear serious 

 examination, as we have shown in our treaties on climates. It is pos- 

 sible, however, to make an advance in the study of this question, by 

 taking into account some facts not yet mentioned. 



Observations upon temperature made in the interior of trees taken in 

 isolated places, and at the periphery of their branches, show, as we 

 have said, that trees act like other bodies when exposed or not exposed 

 to the solar rays ; that is to say, they become warm or cool, according 

 to their absorbing, reflecting, or conducting power, which further shows 

 that their thermal condition depends in a great degree upon the solar 

 action. What may we infer relative to the influence of trees upon the 

 temperature of the air and the changes that come from clearing? These 

 changes come not only from the causes that we have mentioned, but 

 also, as we need not repeat, from the nature of the soil ; as whether dry 

 or damp, calcareous, sandy, or argillaceous. Let us analyze the effects 

 that these may produce. 



Let us first consider a wooded soil. The trees become warm or cool, 

 as already described; but what effect does this have if the soil is dry or 

 moist ? If dry, there will be no effect*. If moist, the evaporation of the 

 water will produce a constant humidity, which will depend in degree 

 upon the temperature which the trees acquire, independently of that re- 

 sulting from the transpiration Irom the leaves. The humidity, all things 

 else being equal, which may be caused by the trees, should be greater 

 in a wooded country, and on an argillaceous soil, which will retain 

 the water because the roots do not pierce it, or penetrate with difficulty 

 into the subsoil, which, if sandy, would favor the infiltration of water. 

 In this case, the humidity would be only such as comes from the evap- 

 oration of the leaves. 



What would happen when we clear a country with an impervious or 

 a pervious soil ? The effects would depend on the composition of the 

 soil, and its i)ower of absorption, radiation, and conduction, and of these 

 we will endeavor to present the ideas of Schubler. 



We will begin by the warming of soils exposed to the sun, and shall 

 find the following conditions in different soils : 



Maximuvi temperature of the upper strata, the mean temperature of the air 'being 100. 



Desimation of soils. 



"loa!' i^^-^-i- 



Grayish-yellow silicions sand.. 

 Grayish-White calcareous sand . 



Pure gypsnm 



Yellowish poor clay 



Rich clay 



White calcareous soil 



Grayish-black humus 



Grayish-black garden-soil 



37. -A^ 

 3fi. 5.-. 

 36.75 

 37.25 

 3G.63 

 .39.75 

 37.50 



44.75 

 4-1. 50 



43. 02 



44. 10 

 44.50 

 43. 00 

 47.37 

 45.25 



We see that color and humidity are causes that exercise the greatest 

 influence. The difference of temperatue due to these causes, with that 

 of the ambient air, in the same soil, may amount to 14 or 15 degrees. 



If we pass to the i)roperty of retaining heat, we shall find that, all else 

 being equal, the silicious.aud calcareous sands, as compared with equal 



