Natural Regeneration, unthinned, poorly stocked, dense bru 



1 6 



LU 4 



o * 



CO 







M= 3.0 



1I1L 



1940 '42 '44 '46 ' 48 * 50 '52 



YEAR 



Figure 5. — Snow W.E. gains on recovery plot, south slope 



66 ' 68 7 7 2 74 



Once timber is cleared, the south slope opening presents an even more hostile 

 environment for conserving snow. Subjected to considerable wind scouring, increased 

 winter melting, and greater surface evaporation/sublimation , the clearing registers a 

 smaller net increase in snow W.E. than a comparable opening on a north slope. 



Climatic and Vegetative-Recovery Trends 



On the north slope a greater depth of snow W.E. was measured in the recovery plot 

 during the 1942 to 1952 period than in the interval from 1967 to 1974 (fig. 6). The 

 levels or intercepts of the two regressions are significantly different (P<=0.04). This 

 may be interpreted as a time-dependent decrease in snow W.E. gains. The curves lie well 

 above the "100 percent recovery" line, a theoretical point in time when the structure of 

 the timber on the recovery plot approximates that of the surrounding forest. 



The apparent downward trend was tested by adjusting for year-to-year variations 

 in winter precipitation and mean winter temperature (measured at headquarters station) . 

 Results of the test after including a time-trend variable are presented in table 3. 



8 



