SUMMARY AND CONCLUSIONS 



A study of the changes in snow accumulation and melt following timber harvest was 

 conducted in a young mature-mature stand of cedar-hemlock-white pine in north Idaho. 

 On the steep north slope, the immediate response to clearcutting was a 56 percent 

 increase in peak snow W.E., most of which was associated with savings from interception 

 loss. This pattern persisted until the new stand became established. After 26 years, 

 a thinning of the untouched sapling stand reduced stems from 3,320 to 400 per acre 

 (1,344 to 162 stems per hectare). Thirty-four years after clearcutting, a downward 

 trend in peak snow W.E. was evident, although the overall increase remained a substan- 

 tial 37 percent. 



Based on the current trend, the gains will probably continue to diminish until the 

 next thinning, scheduled for 1985. Reduction in crown-cover density at that time 

 should reverse the trend and bring about a brief upswing in snow W.E. gain. The sequen- 

 tial pattern of decline followed by brief rise should be repeated, though in declining 

 magnitude, at the time of commercial thinning in 2005 and again in 2045. By the end of 

 the 100-year rotation, the managed stand should be accumulating more snow than an 

 unmanaged stand of comparable age. 



On the steep south slope, clearcutting resulted in a smaller peak snow W.E. in- 

 crease of 37 percent. This average gain persisted after 34 years--even though the new 

 stand was being slowly established. The silviculture plan called for no thinning, and 

 unless the stand is thinned in the foreseeable future the gains will eventually decline. 



Spring snowmelt rates were accelerated after clearcutting on the north and south 

 slopes by 45 percent and 44 percent, respectively. After thinning the new north slope 

 stand, melt rates declined over the years as crown-cover density increased the amount 

 of shade. By the end of the evaluation period, melt rates were fully recovered and in 

 fact were slightly less than those in the residual mature timber. Based on findings of 

 other research we conclude that the minimum melt rate has been nearly reached in the 

 sapling stand and will gradually increase as the crown-cover density approaches 1.00. 

 The low melt rates provide the advantage of delayed snow disappearance, and should delay 

 infiltration and subsurface flow to the stream channel at the time when bank-full vol- 

 umes would be hazardous to channel stability. 



On the south slope, the progress of stand reestablishment (unthinned) was proceed- 

 ing slowly because of brush competition. Reduction of the high melt rate was not 

 detected. Maintaining a pattern of accelerated melt rate is desirable in south slope 

 clearcuts. First, it represents a practical hydrologic method for rushing melt water 

 out of the system before high flows of other subdrainages in the watershed collect and 

 contribute to the peak runoff. Second, the early disappearance of snow from south slope 

 openings exposes browse forage sooner and at a time when most needed by big game. 



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