58 Eleventh Annual REroRT 



made in different parts of the globe extending back for a period 

 of several hundred years would be required to determine this point 

 definitely ; but, unfortunately, such records are lacking. The avail- 

 able data on the subject show that certain local effects are pro- 

 duced by forests, but the temperature and precipitation of a region 

 are not materially influenced or controlled by them. A few records 

 in the United States date back to a time when the country was 

 largely forested, and comparison made between these and records 

 made since the forests were removed, indicate that no important 

 or distinctive changes in temperature or precipitation have taken 

 place as a result of such removal. 



Experiments along this line are being conducted jointly by the 

 United States Bureau of Forestry and the United States Weather 

 Bureau. A station has been established at Wagon Wheel Gap, 

 Colorado, for this purpose. Observations are being made in and 

 near certain forested slopes, where, after a number of years have 

 elapsed the forests are to be removed and the observations contin- 

 ued for a similar period of time. Meteorological observations are 

 also being made regularly in some of the other forested sections 

 of the country. It is very probable that the data thus obtained 

 will afford new and valuable information on this important subject. 



The precipitation that falls in Indiana, as well as in the other 

 central States, is brought chiefly from the Gulf of Mexico by the 

 southerly winds that attend the passage of large cyclonic areas, 

 which cross the country from west to east at frequent intervals. 

 Very little moisture is brought to this section from the Pacific 

 Ocean, as the moist winds from that body of water give up the 

 greater part of their moisture content by the cooling process in- 

 volved in crossing the mountain ranges of the western States, This 

 explains the semi-arid condition of the Great Basin and the eastern 

 slope of the Rockies. By similar reasoning, the heavy rainfall 

 on the north Pacific slope during the winter months is produced 

 hy the cooling of the moisture-laden winds, which, as they ascend 

 the slopes of that region, must give up a large portion of their 

 moisture. It is evident that the rainfall of a locality may be 

 brought to it over great or short distances, and that the moisture 

 is precipitated by changing temperature conditions regardless of 

 the nature of the surface covering of the earth. In view of this 

 fact, it is only reasonable to believe that the heavy growth of for- 

 ests in regions of heavy rainfall and their absence in semi-arid 

 regions is the effect rather than the cause of such climatic con- 

 ditions. 



