316 



FORESTRY INVESTIGATIONS U. S. DEPARTMENT OF AGRICULTURE. 



SANITARY INFLUENCE. 



(1) Tlie claimed influence of greater purity of the air due to greater oxygen and ozone pro- 

 duction docs not seem to be significant. (P. 171, Bui. 7.) 



(2) The protection against sun and wind and consequent absence of extreme conditions may 

 be considered favorable. (P. 171, Bui. 7.) 



(3) The soil conditions of the forest are unfavorable to the production and existence of patho- 

 genic microbes, especially those of the cholera and yellow fever, and the comparative absence of 

 wind and dust, in which snch microbes are carried into the air, may be considered as the principal 

 claim for the hygienic significance of the forest. (P. 172, Bui. 7.) 



We may summarize that the position of the forest as a climatic factor is still uncertain, at 

 least as to its practical .and quantitative importance, but that its relation to water and soil condi- 

 tions is well established. As a climatic factor, it would appear that the forest of the plain is of 

 more importance than that of the mountains, where the more potent influence of elevation 

 obscures and reduces in significance the influence of their cover; as a regulator of water condi- 

 tions, the forest of the mountains is the important factor; and since this influence makes itself- 

 felt far distant from the location of the forest, the claim for attention of Government activity and 

 for statesmanlike policy with reference to this factor of national welfare may be considered as well 

 founded. Every civilized government must in time own or control the forest cover of the moun- 

 tains in order to secure desirable water conditions. 



In conclusion, I may urge that systematic observations bearing on the subject of forest influ- 

 ences should be instituted in this country by a Government agency, perhaps under the authority 

 of the Weather Bureau and with the cooperation of the agricultural experiment stations. No 

 other country is so well adapted for the study of this question as tiie United States, ottering all 

 the varying climatic conditions of a whole continent under one government, witli changes in 

 forest conditions constantly progressing. 



GRAPHIC ILLUSTRATIONS. 



The following diagrams, reproduced from Bulletin 7, represent more in detail, yet in a succinct 

 manner, the results of the long-extended series of observations by the Prussian forest- meteoro- 

 logical stations. These stations were double stations; i. e., one set of instruments was placed in 

 the forest and a corresponding set at some distance from the forest in open fields. The stations 

 represent varying conditions in geographical and topographical location and in character of forest 

 growth. At Lintzel there was only one station, originally in an extensive open heath, which was 

 gradually planted to forest, allowing an observation of changes due to these changed conditions. 



The conditions at the various stations were as follows: 



German stations for forest meteorology. 



