might be realized by changing either the spe- 

 cies or character of existing plant communi- 

 ties. The primary purpose of these changes 

 would be to reduce moisture loss below the 

 surface 3 feet by reducing rooting depth. 



If the aspen were removed, we would ex- 

 pect that uncontrolled sprout growth would 

 quickly reduce the benefits of the treatment 

 on water yields. A plot study conducted on 

 the experimental watersheds demonstrated 

 that soil moisture losses were reduced by 3 or 

 more inches in each of the first 4 years fol- 

 lowing aspen clearcutting (Johnston 1969). 

 The results of soil moisture measurements in 

 the 0- to 3-foot and 3- to 6-foot depths on 

 both clearcut and mature aspen plots is pre- 

 sented in figure 14 for the second, third, and 



fourth seasons after cutting. No attempt was 

 made to control sprouting. By the fourth 

 year, reduction in depletion in the surface 3 

 feet had been largely eliminated while deple- 

 tion differences in the 3- to 6-foot level re- 

 mained fairly constant. The pattern of with- 

 drawal did not change greatly from the fourth 

 through the seventh year indicating that treat- 

 ment effects may be more persistent than pre- 

 viously expected. 



Evapotranspimtion 



Potential evapotranspiration (PE) com- 

 puted according to the Thomthwaite method 

 (Thornthwaite 1957), is largely based on 



Z 

 ui 

 I- 

 Z 



o 

 u 



oc 

 til 



10 

 9 



8 



t- 

 ai 



u. 7 

 n 



° 6 

 5 

 4 



v\ 



*»3 • 



CLEARCUT 

 MATURE ASPEN 



1 







V 



A S 

 1965 



i-r-n 



1 £ 

 < 



oc 







A 

 1966 



A S 

 1967 



Figure 14. — Moisture content in the first 3 feet (0-3 feet) and the second 3 feet (3-6 feet) soil 

 profile. Measurements for 1965 represent the second summer after clearcutting. 



18 



