Estimating Additional Water Yield from Changes in Management

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; ?The Deadhorse Creek Watershed and its sub drainages were used as pilot demonstration areas to evaluate management strategies that represented ca 1980 thinking on increasing water yield through timber harvest. The circular clear cuts imposed on the North Fork, and the irregular clear cuts in the Upper Basin (figure 4), were expected to result in an increase in flow. The shelterwood cut imposed on the North Slope was not expected to result in a significant increase in flow. The first treatment imposed on Deadhorse Creek occurred on the North Fork sub drainage in 1977. Timber was removed on 36 percent of the land area (figure 4) by commercially clear cutting 12 small circular units, uniformly spaced through the drainage. The circular openings were about SH (H= tree heights) in diameter, and occupied about 3 acres each. Harvesting was completed in the summer of 1978. During the summers of 1983 and 1984, approximately 30 percent of the Upper Basin was harvested in irregular-shaped clear cuts, varying in size from 1-15 acres. Approximately 95 percent of the basal was removed in the clear cuts on both sub drainages. The residual basal area represented either non-commercial trees or advanced regeneration. Some snags were left standing to provide wildlife habitat. h= The SH circular clear cuts imposed on the North Fork were intended to !maximize snow pack accumulation in the clear cuts and to optimize flow increases for the basal area removed (Troendle and Leaf 1980). The irregularly shaped openings placed in the Upper Basin were designed to blend with the surroundings and create less visual impact than the circles, increase edge effect for wildlife, and result in increased snow pack accumularion and water yield. In contrast, it was reasoned that partial cutting, as proposed for the North Slope, Unit 8, would have little effect on stream flow because: (1) in a semi-arid environment such as the sub alpine (Leaf 1975), the residual stand would have access to and use any transpiration savings during the growing season; and (2) without clear cutting and the attendant aerodynamic changes in the canopy there would be no redistribution of snow and no net change in the deposition pattern of the winter snow pack; thus the efficiency in delivering water to the stream would not be enhanced. The hypothesis resulting from these assumptions were that the partial -cutting (harvesting by individually marking trees for removal or thinning) would be far less efficient in increasing stream flow than would be the removal of the same percentage of the forest in small (5- 8H) clear cuts as imposed on both the North Fork and Upper Basin. ? 8