INTRODUCTION 



The mixed-species conifer forests of north Idaho, northeastern Washington, and 

 western Montana represent the highest major water-producing zone in the interior West. 

 Precipitation amounts are high, ranging from 30 to 80 in (76 to 203 cm) , with more than 

 one-half accumulating in a snowpack from November through April. The removal of tree 

 cover by clearcutting in patches, strips, or blocks greatly accelerates the winter 

 storage of snow and thus increases the amount of water available to streamflow. 



Augmentation of water yield represents a desirable goal of timber harvest but must 

 be carefully controlled to avoid adverse effects on water quality and channel stability. 

 To accomplish this goal, Forest Service hydrologists emphasize water quality as timber 

 sales are designed, stressing that harvesting in a given watershed must proceed grad- 

 ually to prevent an imbalance in the streamflow regime. Additionally, when reentering 

 a partially logged watershed, the reduction of water yield with vegetative recovery must 

 be evaluated before deciding on how much new timber wil] be harvested (USDA Forest 

 Service 1973). Hydrologists in this region presently have very little documented evi- 

 dence on the rise and fal] of water yield as a timber stand is cut and subsequently 

 revegetated . 



Increases in water yield are generally proportional to the reduction in forest 

 canopy, as well as to the intensity of partial cutting or percentage of clearcut area 

 (Stone 1973) . The duration of the yield increase depends on how rapidly roots reoccupy 

 the soil and how quickly the canopy is reestablished. Canopy reestabl ishment directly 

 affects snow accumulation. 



Generally, research shows that gains in snow accumulation can be expected to persist 

 longer than gains in soil water (Anderson 1969) . Increased snow accumulation in lodge- 

 pole pine in the central Rocky Mountains will apparently persist for many decades and 

 perhaps indefinitely (Gary, in press) . In California, soil water gains on level terrain 

 were negligible 16 to 20 years after clearcutting (Zeimer 1964). 



In a recent study in north Idaho, soil water gains on a steep south-slope clearcut 

 disappeared within 4 years after the climax understory brush reoccupied the area (Cline 

 and others 1977). In the same study, soil water increases were present for at least 

 5 years on a north- si ope clearcut because herbaceous plants reinvaded and dominated the 

 clearcut early in the recovery period, although the deeper-rooted brush was making rapid 

 inroads by the fifth year. By extrapolation of the data, it would appear that the 

 north-slope soil water gains would approach zero earlier than the 16 to 20 years observed 

 in the California study. In contrast, on both the north and south clearcuts no downward 

 trend in snow accumulation gains was evident 5 years after harvest (Cline and others 

 1977). 



This paper reports changes in snow accumulation gains on another site clearcut 

 34 years ago in the same general area. A paired-plot comparison was made between the 

 clearcut and an adjacent stand of mature timber. Records were obtained periodically 

 beginning with the second year and ending with the 34th year after harvest. 



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