The structure of timber on the forest control plot was assumed to have changed over 

 the 34-year evaluation period. To test this assumption, a time-trend analysis was 

 performed, including climatic data recorded at the PREF headquarters station (elevation 

 2,380 ft [725 m]). Data for the vegetative recovery plot were similarly analyzed to 

 determine if vegetation had recovered enough to have affected snow accumulation and 

 melt. In other tests, water-equivalent changes in the snowpack over time were compared 

 using regression techniques. 



PEAK SNOW ACCUMULATION 



Harvesting Effect 



On the north slope, the removal of the young mature timber resulted in average snow 

 W.E. gains in the vegetative recovery plot of 7.6 in (19.3 cm) for the period 1942 

 through 1952 (table 2). This was the period of early stand reestabl ishment and develop- 

 ment (fig. 2). The average yearly gains compare favorably with those of 6.6 in (16.8 cm) 

 measured in a narrower strip (200 ft [61 m]) cut in mature-overmature cedar-hemlcck- 

 white pine 1,000 ft (305 m) higher in elevation (Haupt, in press). Most of the snow 

 accumulation increase was the result of snow caught in dense canopies that would have 

 evaporated/sublimated had the trees not been harvested. Another portion of the increase 

 was probably the result of wind eddy-forest edge effect during storms, and a fractional 

 increase was perhaps due to slower winter release of water from the snowpack in the 

 opening compared with the forest (Haupt 1972, in press). Gains on the recovery plot 

 are shown in figure 4. 



A. 



Figure 3. — Aerial view of strip olearcut taken May 1966 (arrows denote study plots). 

 A. North- facing slope before thinning. B. South- facing slope. 



5 



