Influence of Forkst.s on Natukai, Watkh-.Si'im-i.y. 



1 r 



«n-aj>orati'iii. Butli these are induced bv detorestatioii aii<l nii)iiiiiis<>d 

 hv tree-phintii).ii. It is scarcely necessary to discuss the difference 

 between the teniperatuie in an open tield and in a shaded wodd-lot. 

 All tiees absoib moisture from tlie soil and exiiale it through the 

 .stomata of the leaves. It is simply a matter of physics that (najiora- 

 tion consumes heat and lowers the temperature. It is also natural 

 that without air currents, and with a cool, more or less saturate<l 

 atmosphere, the evaporation must be small. Then the leaf mould 

 acts as a liighly eflicient mulch and prevents evaporation fi-om the 

 soil itself. The experiments of M. Mathieu show that the evaporatii>n 

 from a sheet of water is much less undei- trees than outside, and that 

 in a leafv forest the proportion, which is 1 to 2 during the coUl season, 

 becomes 1 to 4 during the summer.* Direct observations made in 

 Bavaria and Prussia show that evaporation in tlie forests was only 

 two fifths of that in the open country. Dr. Ebermayer's experiments, 

 extending over five years, give the following results : — 



Evaporation of water from soil in open = 1 00 



Evapoiation of forest soil, without leaf mould = 47 



Evaporation of f,>rest with a full layer of leaf mould = 22 f 



Observations on the evaporation from sheets of water in forests, and 



from those in an open space, have been carried on at three different 



stations in Sweden, and give remarkable i-esults. 



Dalb.Mla 



Stations. 



May. June. Jidy. Aug. 8ep. 



j ( )pen space, nun 



Under tlie trees, nnn.... 

 I ,, per cent. 



120-9 \Ut< 131-0 99-7 53-6 

 34-1 4(3-4 41-8 28-1 23^1 

 28 32 32 38 43 



The foregoing is the mean for the years 1880-89,;; and it is 

 interesting to note that the highest percentage was oVitained at Spar- 

 hult, where the forests are less thick. 



Similar results have been obtained in Hawaii, where the evapora- 



* TraiU de St/lvkii/tiirc, by I*. Mouillefert, )•. 14. 

 t Manual of F<j nut rij, by Wm. Schlich, C.I.E., Ph.D., p. 44. 

 ;: liifiifiiri of Fiirr.s'fs- i/'/i f/ii <'/i,/i"fe of Sirnhn, by Dr. H. K. H.-miberg, 

 )iart iv, Eaux tonibces. 



