Science has not been able to determine what has been the 

 precise influence of the removal of forests on the natural circu- 

 lation of waters. Where vegetative cover is completely 

 removed there is lost the transpiration and evaporation which 

 are believed by many authorities to have considerable influ- 

 ence on the formation of clouds and on temperature, and 

 therefore possibly on the volume and distribution of rainfall. 

 It has been estimated that, depending on regional climatic 

 conditions, a given store of water which has been blown in over 

 the land from the ocean in the form of clouds may be "work- 

 ed" three to five times as rainfall, because of alternations of 

 evaporation and transpiration with precipitation, before it 

 returns to the ocean as stream flow. Data are not available 

 to warrant a definite statement concerning this phase of the 

 hydrologic cycle. 



The influence on absorption, infiltration, the groundwater, 

 and run-off is more observable and measurable. Lumbering 

 operations are immediately followed in most instances, if no 

 other force intervenes, by rapid growth of brush and saplings. 

 The roots, litter, and humus tend to protect the capacity 

 for absorption and infiltration. Therefore, under the as- 

 sumption that no other force intervenes, the removal of stand- 

 ing timber, generally speaking, has only moderate, if any, 

 unfavorable influence on the absorption and percolating 

 capacity of the underlying humus and soils, and on the 

 mechanical retardation of run-off. 



But other forces have been permitted to intervene. In the 

 first place, as has been indicated, a large proportion of the 

 land from which forest cover has been removed during the 

 past hundred years, has been completely cleaned and made 

 cultivable. This substitutes the influence of cultivation on 

 absorption and percolation, which will be considered later, 

 for the influence of forest cover. 



In the second place, forest fires have been permitted to 

 devastate cut-over lands. Slashings are especially suscepti- 

 ble to fire, and people are careless about fires in slashings 

 "because the valuable timber has been removed." They do 

 not realize that elements more valuable than the timber the 



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