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? <br />? <br />? ?m? United States <br />? Department of <br />Agriculture <br />Forest Rocky P.O. Box 25127 <br />Service Mountain Lakewood, CO 80225-0127 <br />Region Delivery: 740 Simms Street <br /> Golden, CO 80401 <br /> Voice: 303-275-5350 <br /> TDD: 303-275-5367 <br />File Code: 2520 <br />Route To: (planning), (Fire), (Vegetation Management) <br />Subject: Water Yield Enhancement <br />Ta: Forest Supervisors and RO Staff Directors <br />Date: July 12, 2002 <br />Recently, some of you have raised questions about Region 2's approach to Water Yield <br />Enhancement through Forest Planning. In addition, during this drought year, water supply is of <br />critical concern to all of our constituents, and you may be receiving inquiries about the <br />relationship between forest management and water yield. This letter is to clarify the Region's <br />direction for water yield enhancement and provide a rationale for our approach. <br />Based on experience from the first round of forest planning, and updated research, the Region <br />has elected not to emphasize water yield increases through a specific management area <br />prescription in Forest Plan revisions. Implementation of normal timber management and fuels <br />reduction prescriptions will result in modeled water yield increases. The Management Area <br />Prescription for Water Yield (Management Area 5.21 Water Yield, formerly 9B) has been <br />retained in the Planning Desk Guide menu of optional management area prescriptions, but has <br />not been used in Forest Plan revisions. The potential for water yield enhancement is generally <br />analyzed in the effects analysis for the Forest Plan. <br />The rationale for this approach is as follows: <br />1) The primary influence on water yield in large basins is precipitation, which is variable in <br />the short term, but relatively constant in the long term. <br />2) Research on small watersheds shows that although basal area reduction of forest cover <br />does increase water yield, these yields are independent of any particular silvicultural <br />prescription. Therefore, water yield increases are modeled to result from implementation <br />of normal timber management and fuels reduction prescriptions. <br />3) Research shows that to achieve measurable on-site water yield increases in any size of <br />watershed, a large percentage (25% or more) of the basal area in that watershed would <br />have to be removed at once. Generally it is undesirable and often infeasible to make this <br />significant of a change on larger landscapes due to physical, biological, legal, and <br />practical constraints. <br />a Caring for the Land and Serving People Printed on Recycled Paper ??