266 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1915. 



climatic conditions that have prevailed in that region for a long 

 time. It expresses not only the result of one single climatic factor, 

 but is the product of all the climatic and physical factors together. 

 Similarly, the use of the na1;ural forest types for determining the 

 potential capacity of the land occupied by them for different pur- 

 poses is beco'ming more and more appreciated. When the climatic 

 characteristics of a certain type of forest, for instance those of Engel- 

 mann spruce in the Rocky Mountains, is thoroughly established, the 

 potential capacity of the land occupied by it for agriculture, grazing, 

 or other purposes is also largely determined. 



Observations of the effect of climate upon forest growth naturally 

 brought out facts with regard to the effect of forests upon climate, 

 soil, and other physical factors and led to the development of a 

 special branch of meteorology, known as forest meteorology, in 

 which the foresters have taken a prominent part. While there are 

 some phases in forest meteorology which still allow room for dis- 

 agreement, some relationships established by foresters are widely ac- 

 cepted. One of these is the effect which forests have upon local 

 climate, especially that of the area they occupy and of contiguous 

 areas. Every farmer who plants a windbreak laiows and takes ad- 

 vantage of this influence. Another relation is that between the 

 forest and the circulation of water on and in the ground, a relation 

 which plays such an important part in the regimen of streams. 

 Still a third one, as yet beyond the possibility of absolute proof, is 

 the effect of forests in level countries, in the path of prevailing winds, 

 upon the humidity and temperature of far-distant regions lying in 

 their lee. 



If in the field of botany the forester has contributed to the progress 

 of botanical geography and in the realm of meteorology has opened 

 hew fields of investigation, his influence in wood technology has been 

 in changing entirely the attitude of engineers, physicists, and chem- 

 ists in handling wood products. The methods of studying the 

 physical, mechanical, and chemical properties of wood were, of 

 course, those used in engineering by chemists and physicists ; but the 

 forester has shown that wood, unlike steel, concrete, or other struc- 

 tural material, is subject to altogether different laws. Wood, he has 

 shown, is not a homogeneous product, but is greatly influenced by 

 the conditions in the stand from which it comes. Were it not, there- 

 fore, that mechanical properties can be tied up with some definite 

 forest conditions and correlated with some readily visible expression 

 of tree growth, such as the number of rings per inch or the specific 

 gravity of the wood, timber would be too much of an indefinite 

 quantity for architects and other users of wood to handle with 

 perfect safety. To find such a relation is just what the foresters 

 have been attempting to do, and most of the studies of the strength 



