312 FORESTRY INVESTIGATIONS U. S. DEPARTMENT OP AGRICULTURE. 



of condensation, which a heated plain would do; but observations so far give no conclusive 

 evidence that neighboring fields receive more rain than they otherwise would. (Pp. 76, 83, 89, 

 103, Bui. 7.) 



(4) With regard to comparative temperatures in forest stations and open stations that are 

 situated not far apart from each other, it would appear that the forest exerts a cooling influence, 

 but that more detailed conclusions are hindered by the consideration that the ordinary meteoro- 

 logical 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 tempera- 

 ture. Similar studies for stations in the United States seem to show that our thin forests 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 

 temperature is dependent upon the quantity or distribution of forests or that changes in tempera- 

 ture have occurred from this cause. (Pp. 94, 95, Bui. 7.) 



(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 situations it is found that the mean range of temperature is larger in the glade than in the 

 open; 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. (Pp. 84-88, Bui. 7.) 



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 prevails. Here the forest growth is able to diaw 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 would be less effective or of no use. Hence in regions 

 with oceanic climate, with moist sea winds, like England and the west coasts of Europe or of the 

 northern United States, deforestation from a climatic point of view may make no appreciable 

 difference, such as it would make in continental climates like the interior of our country, the Bocky 

 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 discussed, since we are not clearly informed even as to the 

 manner and the amount of influence which forest cover exercises. In general, Ave may expect 

 that an alternation of large forested and unforested areas in regions which on account of their 

 geographic situation have a dry and rigorous climate is more beneficial than large uninterrupted 

 forest areas, which would fail to set up that local circulation which is brought about by differences 

 in temperature and permits an exchange of the forest climate to the neighboring field. 



More recent experiments tend to modify somewhat the conclusions arrived at heretofore, and 

 indicate, as has been suggested, that the differences in temperature and humidity of woods and of 

 open land that have been recorded are largely to be attributed to variability of instruments and 

 of readings, and to nonconformity of conditions. 



Even the well-planned Austrian experiments have produced neither striking nor consistent 

 results. In 1893, Dr. Lorentz Liburnau concluded that forests did not cool the air of the 

 surrounding country, and that temperature extremes were even heightened in the immediate 

 vicinity of the woods. Concerning humidity, it was found that while with one set of stations this 

 appeared increased by an uncertain trifle through the proximity of the forest, in another set no 

 influence was observed, and in one case the air current from the woods was positively drier at 

 noon time than that of the open country, and even though Lorentz Liburnau is still hopeful in 

 the matter he felt compelled to admit that a u distance effect" of forest influence was so far not 

 demonstrated. 



Schubert, in 1895 and again in 1897, published results of extensive temperature measurements 

 which point to an entire absence of influence in this respect, the air of the forest being in no case 

 sufficiently cooler to warrant a decision. His experiments gave a difference of only 5° F. in favor 

 of the pine woods. This author came to practically the same conclusion regarding the humidity 

 of the forest and the open country. 



Miittrich, in 1896, comparing different modes of placing the thermometers found that these 

 thermometers side by side varied by as much as 1.2° F. 



In a recent investigation of the methods employed in investigations of this character Hoppe 



