TEMPERATURES IN AND OUTSIDE OF FORESTS, 19 



appear that the forest exerts a cooling iDfliieiice, but that more de- 

 tailed conclusions are hindered by the consideration that the ordinary 

 meteorological station itself is somewhat affected by neighboring trees. 



The study of the stations in Asiatic and European Eussia seems to 

 show that in the western part of the Old World the presence of large 

 forests has a very sensible influence on the temperature. Similar 

 studies for stations in the United States seem to show that our thin for- 

 ests have a slight effect in December but a more decided one in June. 

 It appears also that our wooded regions are warmer than the open 

 plains, but there is no positive evidence that this difference of temper- 

 ature is dependent upon the quantity or distribution of forests, or that 

 changes in temperature have occurred from this cause. 



(5) When a forest incloses a small area of land, forming a glade, its 

 inclosed position brings about special phenomena of reflection of heat, 

 local winds, and a large amount of shade. For such forests it is found 

 that the mean range of temperature is larger in the woods than on the 

 open plain; the glade climate is more rigorous than the climate of open 

 plains; the glade is cooler and its diurnal range larger during the 

 spring, summer, and autumn. 



Favorable influences upon moisture conditions of the air are most 

 noticeable in localities where much water is stored in underground with 

 overlying strata which are apt to dry when our summer drought pre- 

 vails. Here the forest growth is able to draw water from greater depths 

 and by transpiration return it to the atmosphere, thereby reducing 

 the dryness and possibly inducing precipitation. In most climates this 

 action Avould be less eflective or of no use. Hence in regions with 

 oceanic climate Avitli moist sea winds like England and the west coasts 

 of Europe or of the northern United States, deforestation from a cli- 

 nuitic point of view m;iy make no ap[>reciable difference, such as it 

 would make in continental clinmtes like the interior of our country, the 

 llocky Mountains, and southern California. 



Whether large or small areas of forest and open fields alternating, 

 or what percentage of forest is most favorable can not as yet be dis- 

 cussed, since we are not clearly informed even as to the manner and the 

 amount of influence which forest cover exercises. In general we may 

 expect that an alteriiation of large forested and unforested areas, in 

 regions which on account of their geographic situation have a dry an«l 

 rigorous climate, is more beneficial than large uninterrupted forest 

 areas, which would fail to set up that local circulation whicli is brought 

 about by differences in temperature and permits an exchange of the 

 forest climate to the neighboring field. 



