ASPEN (M) 



ASPEN (S) 



Figure 2. — Range of 

 evapotranspiration 

 estimates for 

 several vegetation 

 types . 



DOUGLAS-FIR 



GAMBEL OAK (M) 



GAMBEL OAK (S) 



SAGEBRUSH-GRASS 



SNOWL'ERRY (M) 

 SNOWBERRY (S) 



GRASS HERB 



BARE 



M - MATURE 

 S - SPROUT 



0.5 

 _J 



1.0 



1.5 



2.0 



2.5 



3.0 



3.5 



Jm 



EVAPOTRANSPIRATION 



(Inches per foot of soil measured) 



CONCLUSIONS 



Results of all studies indicate that moisture depletion is greatest early in the 

 growing season (May to July) and that late-season losses generally are confined to 

 withdrawal from deeper parts of the soil profile. By the end of each summer, most of 

 the available soil moisture throughout the rooting depth is depleted. 



On paired plots, mature aspen stands utilized 0.48 to 4.50 inches more soil 

 moisture from the upper 6 feet of profile than sprout stands. These differences 

 diminish rapidly after the first year as sprout stands mature and evapotranspiration 

 accelerates. Comparisons of evapotranspiration losses on Gambel oak plots show mature 

 oak utilizes only 0.25 to 1.15 inches more moisture from the upper 6-foot soil profile 

 than 1-year-old sprout stands. In two instances, 3-year-old oak sprouts had greater 

 evapotranspiration losses than mature stands. Removal of oak and aspen can prolong 

 water savings only if sprouting is prevented. 



An indication of prospective water savings following conversion of aspen to grass 

 can be obtained from moisture measurements on sites 1, 2, 5, and 6. Reduced 

 evapotranspiration losses ranged from 1.08 to 5.18 inches from 6-foot sampling depths 

 and 2.76 to 7.59 inches from a 9-foot soil profile. The average reduced water 

 consumption on plot 5 was 5.75 inches for the 4-year period. Conversion of Gambel oak 

 to grass (site 4) reduced evapotranspiration losses by 4.55 and 3.83 inches from an 

 8-foot-deep soil. 



Shallow-rooted plants extract less water from depth than deep-rooted vegetation; 

 this is the premise upon which all vegetation conversion practices tor increased water 

 yields are based. The difference in evapotranspiration losses before and after treat- 

 ment is water saved. Eventually, such water will emerge as streamflow or will be stored 

 in the groundwater aquifer. Obviously, treatments will be most beneficial on sites 

 showing the greatest decrease in rooting depths. 



6 



