Table 7 AB — Summary of estimated annual yield increases which could be achieved in the 



Northwest through vegetation management 



Hydrologic zone 



Vegetation type 



Annual yield increase 







Thousand 







acre-feet 



1. Coastal rain zone 



Douglas-fir, hemlock, Sitka spruce 



2.100 



2. Puget-Willamette rain zone 



Douglas-fir, hardwoods 



400 



3. Warm snow zone 



Fir-spruce ) 





4. East Cascades snow zone 



Ponderosa and lodgepole pine) 



2,570 



5. Interior cold snow zone 



Douglas-fir, lodgepole pine, ) 

 ponderosa pine, white pine ) 





Total 





5,070 



Source: Wooldridge, David D. Opportunities for increasing water supplies in 

 the Pacific Coast States by vegetation management. Unpublistied rep. on file at 



the Forest Hydrology Laboratory, Wenatchee, Wash., 130 p, 1978. 



Timing of increased yield in the Northwest varies 

 with the precipitation zone. In the rain zones, about 

 80 percent of the increase occurs during the wet 

 winter months.''^ Increases amounting to 0.8 inches 

 during the low flow months of July-September^^ are 

 important for instream needs. In the snow zones, 

 most of the yield increase occurs during spring 

 snowmelt. 



Estimated potentials for increasing water yields in 

 the commercial forests of the western States by 

 timber type are summarized in table 7.17. These 

 values are based on several summary reports.''' ''^ '•^ 5o 

 The estimated increases are based on the difference 

 between no management and specific management 

 for water yield increases. 



The chaparral type, which contains several species 

 of shrubsize plants, covers approximately 29 million 

 acres in southern Cahfornia, Arizona, and New Mex- 

 ico. Intensive research during the past few years 

 indicates that opportunities for increasing water sup- 

 plies from the chaparral type are excellent under 

 certain conditions. In areas where shrub cover ex- 

 ceeds 30 percent, average annual precipitation ex- 

 ceeds 16 inches, and soils are deep, substantial 

 increases in water supplies can be produced. '' The 

 most effective treatment is to eradicate the shrubs 

 from about 60 percent of the total treatable area and 



Table 7.17 — Estimated potential for increasing 



water yield from forested lands in the 



western States 



"•^ Rothacher, op. cit. 



"6 Ibid. 



■•^ Wooldridge, op. cit. 



"•^ Hibbert, Alden R. Vegetation management for water yield 

 improvement in the Colorado River Basin: Summary and 

 assessment. U.S. Department of Agriculture, Forest Service, 

 Rocky Mtn. Forest and Range Exp. Sta. (In press). 



■*' Leaf, Charles F, Watershed management in the central and 

 southern Rocky Mountains: A summary of the status of our 

 knowledge of vegetation types. U.S. Department of Agriculture, 

 Forest Service. Res. Pap. RM-142, 28 p. 1975. 



^^Sopper, W. E., op. cit. 



" Hibbert, Davis, and Brown, op. cit. 



Forest type 



Forest 

 area 



Average annual water 

 yield increase 



Douglas-fir 

 Ponderosa pine 

 Western white pine 

 Fir-spruce 



Hemlock-Sitka spruce 

 Larch 



Lodgepole pine 

 Redwood 



Thousand 

 acres 



38,240.2 



33,670.7 



565.9 



113,362.9 



20,139.9 



2,807.2 



21,217.6 



786.0 



Inches 



0.60 

 .15 

 .45 

 .60 

 .45 

 .30 

 .25 

 .45 



Thousand 

 acre-feet 



1,912 



420 



21 



5,668 



755 



70 



442 



29 



Total 



230,790.4 



— 



9,317 



Source: Forest Service estimates derived from: 



Hibbert, Alden R. Vegetation management for water yield improvement in the 

 Colorado River Basin: summary and assessment. Rocky (fountain For. and Range 

 Exp. Sta.. (in press) Wooldridge, David D., see source note table 7. 16: Leaf, Charles 

 F. Watershed management in the central and southern Rocky Mountains: A 

 summary of the status of our knowledge of vegetation types. U.S. Forest Service, 

 Res Paper. RM-142, 28 p. 1975; and Sopper, W. E. Watershed management: water 

 supply augmentation by watershed management in wildland areas. Report to the 

 National Water Commission. NTIS, Springfield, Va. 149 p. 1971. 



estabHsh a grass cover. Research has demonstrated 

 that wildlife benefits from these treatments and that 

 fire protection is made easier.'^ An economic analysis 

 with actual conversion costs and assumed benefits 

 indicated a net average annual return of $2.51 per 

 converted acre based on 1972 prices." It is estimated 

 that the annual cost of water production in the 

 chaparral type is $20.45 per acre-foot in California 

 and $18.00 per acre-foot in the Southern Rocky 

 Mountain region, based on 1967 price levels. ^^ 



52 Ibid. 

 " Ibid. 

 '■•Reigner, et. al., op. cit. 



313 



