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Yearbook^ of Agriculture 1949 



source of their water, and they wonder 

 whether they are getting all that might 

 be made available. Knowing, for in- 

 stance, that plants of every kind use 

 water in considerable quantities to 

 maintain life and produce vegetable 

 matter, they speculate as to whether 

 any water might be saved if watershed 

 vegetation could be thinned or even 

 completely removed. 



This conjecture has given rise to 

 long-standing arguments, first brought 

 to a peak by Col. H. M. Chittenden in 

 an article which was published in 1909. 

 Rather significantly, Ghittenden had 

 been studying western water problems 

 for some time and was engaged in the 

 development of water resources for the 

 general region east of the Rocky Moun- 

 tains. He argued that forests diminish 

 total runoff through evaporation and 

 transpiration, and that they are not 

 so valuable in reducing floods as had 

 been believed. This contention was 

 raised by others repeatedly in ensuing 

 years and gained support by engineers 

 and others interested in the develop- 

 ment of water resources. 



Partly as a result of such arguments, 

 people have learned much about the 

 true value of forest cover in watershed 

 protection since those early days, and 

 realize that it serves an extremely im- 

 portant function in stabilizing soil and 

 in reducing floods. 



But on arid western lands the need 

 for water is sometimes so great that 

 people are still willing to take the risk 

 of floods and erosion in order to get 

 it. In the unusually dry but highly de- 

 veloped valleys of the Southwest, men 

 have been heard to say: "Give us the 

 water, clean or dirty we'll take care 

 of the mud somehow!" 



Obviously that kind of talk shows an 

 incomplete understanding of the dis- 

 astrous consequences of soil depletion 

 and erosion or perhaps it shows a 

 loss of perspective, resulting from the 

 extreme need for water in those areas. 

 Anyway, such statements give a pic- 

 ture of how acute water-supply prob- 

 lems can be in the West and how im- 

 portant it is for watershed managers 



to get every drop that can be produced 

 safely on mountain watershed lands. 

 We dare not overlook the chance that 

 Chittenden and others may have had 

 a strong basis for their contentions 

 that there may be areas where vegeta- 

 tion can safely be removed and water 

 yields thereby increased. 



At first glance it does look like a 

 hard problem. For any given area we 

 have to learn whether it is necessary 

 to maintain a complete forest cover 

 and accept the resulting water con- 

 sumption in the interest of protection, 

 or to what extent we can relax this 

 requirement in order to reduce water 

 losses. In working on this problem we 

 must also remember that, wherever a 

 watershed contains merchantable tim- 

 ber, protection may mean depriving 

 people of badly needed lumber and 

 other products. We want to insure rea- 

 sonable use rather than unnecessary 

 protection. 



WHAT HAPPENS TO WATER IN THE 

 FOREST is the basis of forest manage- 

 ment for maximum water yields under 

 safe conditions. 



When snow or rain falls on a forest, 

 some of it is intercepted by the tree 

 crowns and is stored for the time being 

 on leaves and twigs. A large part 

 reaches the ground by dripping from 

 branches or running down the trunk, 

 but a part of it remains on the crowns, 

 where it is lost by evaporation after 

 the storm is over. 



If the yearly precipitation on any 

 area is made up of small storms sepa- 

 rated by periods of clear weather, this 

 evaporation from crowns is high as 

 much as 35 to 50 percent of the yearly 

 total. Where storms are larger and 

 much cloudy weather occurs, the rela- 

 tive amount of crown interception and 

 loss is smaller. Interception varies also 

 with the kind and the density of the 

 crowns : Thick spruces catch and hold 

 more water than thin-crowned pines, 

 while leafless cottonwoods and aspen 

 intercept much less winter precipita- 

 tion than any of the conifers. Hence it 

 should be feasible to cut down the 



