Soil Conservation An Assessment of the National Resources Inventory, Volume 2 (1986) / Chapter Skim
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6. Erosion on Range and Forest Lands: Impacts of Land Use and Management Practices
6. Erosion on Range and Forest Lands: Impacts of Land Use and Management Practices
Pages 163-203
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From page 163... ...
These practices are generally promoted on the basis of their benefits to the grass or trees, and for improved productivity, but what about the effects on soil erosion? Can areas be identified where more effective range conservation or farm forestry programs can yield important secondary benefits for erosion control?
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From page 164... ...
. On rangelands, wind erosion may be more important than sheet and rill erosion in some areas, so the data recorded for the Wind Erosion Equation (WEE)
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From page 165... ...
Soil erosion problems can be identified from the tables in this paper and many inferences drawn from them that will be of use to national policymakers. The benefits of changing land use and applying conservation practices are fairly easy to estimate, if certain critical assumptions can be made.
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From page 166... ...
Thus, efforts to improve range conditions through grazing management or to improve or reestablish improved stands of forage are likely to yield significant erosion control benefits in addition to increased grazing, wildlife, and watershed values. Point sample data from six MLRAs (10, 30, 43, 67, 77, and 81)
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From page 167... ...
Table 1 is a summary of data generated by the University of Minnesota, in which weighted averages for total potential erosion (RKLS) , total actual sheet and rill erosion (USLE)
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From page 170... ...
In MLRA 10, potential cropland would come disproportionately from lands needing forage improvement or reestablishment, which seems consistent with the fact that these same lands were rated as being in poor range condition. Erosion Control Potential in Range Management Range conservationists promote improved range management for many reasons, including soil conservation.
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From page 172... ...
Percent .000.000.00 2.75116,155.00116,155100.00 3.20255,3062.7535,90214.06 8.89135,8663.2086,96064.00 OO.000.00 4.062,5254.060.00 Total509,851 239,01746.88 Total wind + sheet and rill erosion 615,740 257,59641.84 SOURCE: Derived from 1982 NRI. excellent condition, the weighted average C factor associated with excellent condition in that MLRA should also be achieved.
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From page 173... ...
. An exception was made where the WEE was not inversely related to range condition class, in which case it was assumed that improving range condition would not induce more wind erosion, but that the WEE would remain the same.
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From page 175... ...
Erosion Control Potential in Rangeland Improvement Practices The TORI data can also be used to estimate the potential erosion control benefits of applying the conservation practices listed as needed on rangelands. To estimate the soil loss reductions that might be achieved, the point data on acres needing various treatments, by MLRA, were used to prepare a table containing the weighted averages of the RKLS, USLE, and WEE factors.
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From page 177... ...
Multiplying this weighted average by the acreage in the category gave total tons of soil loss, which enabled cumulative percentages for both acreage and soil loss to be generated. Table 8 shows the results of this method for sheet and rill erosion in MLRA 43, and Table 9 provides wind erosion data from HERA 77.
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From page 178... ...
Even the smaller acreace divisions the assumption is that anything represented by four or more points is a statistically reliable number for these purposes. One exception was in the soil erosion groupings used for MLRAs 43 and 77, where some of the categories lacked adequate point data.
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From page 179... ...
· Comparisons with the individual soil characteristics contained in Soils-5 can be made to separate the sample point data by total soil erosion rates compared with the soil loss tolerance limit. There was not enough time to do this, but a computer run could be designed to separate the acreage shown as needing the various TABLE 9 Estimated Wind Erosion on Rangeland, MLRA 77 Weighted ActualAcreage Cumulative Average Cumulative Erosion(100 Percent WindSoil LossPercent (WEE)
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From page 180... ...
Even where erosion rates were highest, the sample NRI data tested suggest that very little of the problem is not feasible to treat, and the application of needed forest management and timber stand improvement practices appears to have the potential of reducing soil erosion by one-third to three-fourths.
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From page 181... ...
Conversion of Forestland to Cropland A great deal of excellent forestland has been lost to crop production in recent years, and more may be lost in the future. One question that can be evaluated easily with the NRI data deals with the impact of future conversion on the soil erosion problem of remaining forestland.
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From page 183... ...
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From page 184... ...
Tables 13 and 14 are calculated in exactly the same manner as the two preceding tables, with the acreage figures aggregated according to estimated forest canopy cover. As can be seen, most of the potential cropland has canopy covers of less than 50 percent, and, in many areas, one-quarter to one-third is associated with a canopy cover of less than 25 percent.
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From page 185... ...
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From page 188... ...
188 .,, o V hi: o .,, U]
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From page 189... ...
Several conclusions emerged. Forestland that is adequately treated has very low soil erosion rates, and the treatment of forestland identified as needing erosion control, if that treatment could achieve good forest cover, has the potential of reducing erosion on those lands by 60 to 90 percent.
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From page 190... ...
Just how much of the grazed forest is in this condition cannot be determined from the NRI data, however Using the 1982 NRI to Evaluate Forestry Program Potential . As the first national statistical sample to include detailed forestry information, the 1982 MRI is of definite interest to the forestry policy community.
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From page 191... ...
It appears possible, from this limited review of the data, to use this information as one basis for identifying the forest opportunities of the nation and for drawing some conclusions about where the payoff of targeted forestry programs would be highest. GENERAL CONCLUSIONS If the primary goal of conservation programs is the reduction of soil erosion, the point source data contained in the NRI data files can be very helpful in analyzing the areas where targeting effort might be most promising.
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From page 192... ...
~ _ _ ~_ _, ~ ~ In performing national program and policy tests, where each NLRA can be used in whole for evaluation, it seems clear that MLRA data will be far more useful, particularly when working with the SCS-oenerated summaries.
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From page 194... ...
Some of the earliest measurements of soil erosion were made by A
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From page 195... ...
than like the empirical form of the USLE. The USLE and its predecessors were very much structured to be nuser friendly, n because by the early 1950s erosion equations were accepted by the USDA-SCS as a tool for tailoring erosion control practices to the needs of specific fields and farms.
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From page 196... ...
196 TABLE 1 Research Evaluating USLE Performance on Rangelands Reference Area of Work Comments Renard et al., 1974 Arizona Used small watersheds; signif icant channel eros ion Renard and Simanton, Ar izona, Explored 1975 New Mexico estimation of erosion factor Osborn et al., 1976 Arizona, Showed New Mexico importance of stone surface cover Simanton et al., 1977 Arizona Showed effect of root Verma et al., 1977 Ar izona Johnson et al., 1980 Idaho Renard, 1980 Ar izona Simanton et al., 1980 Ar izona Tr ieste and Gif ford, Utah 1980 Foster et al., 1981 Utah Dissmeyer, 1982 New Mexico Hart, 1982 Utah plowing and reseeding on erosion control Measured erosion from disturbed and natural plots with artif icial or simulated rainfall Used canopy and ground cover to compute potential erosion for sagebrush control Compared numerous sediment yield formulae Appl fed to smal 1 watersheds on storm basis Used small plots with rainfall s imulator; suggested USLE did not apply well to rangelands Discussed applicability of USLE to r angelands Used subfactor approach in evaluating C (cover ) on rangeland Measured erosion on sagebrush plots with a rainfall simulator
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From page 197... ...
197 TABLE 1 (Continued ) Reference Area of Work Comments McCool, 1982 Renard and Stone, 1982 Simanton and Renard, 1982 Williams, 1982 Trott and Singer, 1983 Hart, 1984 Washington Arizona Arizona, New Mexico Texas, Oklahoma, Iowa, New Mexico California Utah Simanton et al., Arizona 1984 Smith et al., 1984 Texas, Oklahoma Tracy et al., 1984 Arizona Johnson et al., 1984 Idaho, Nevada Theoretical analysis of slope length-steepness factor Correlation of USLE estimates with stock pond yields Evaluated erosivity of air-mass thunderstorms Estimated sediment yield from mixed cover watersheds with modified USLE USLE soil erodibility factor should consider soil mineralogy Fair agreement of USLE with simulated rainfall data; slope factor needs adjustmen t Measured erosion reduction caused by stone surface cover Sediment yield estimates with modified USLE, on watersheds less than 122 hectares and on watersheds with mixed land uses Measured drop-size distribution of air-mass thunderstorms for use in evaluating erosivity Used rainfall simulator and found interpretation of C on ungrazed areas needed refinement
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From page 198... ...
, (1) where PLU is a prior land use subfactor, PC is a plant canopy subfactor, SC is a surface cover subfactor, and SR is a surface roughness subfactor.
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From page 199... ...
Surface roughness influences soil erosion by reducing runoff volume and velocity, and by pending surface runoff to cause deposition. The roughness of a surface is expressed as the standard deviation among heights along the soil surface perpendicular to the slope.
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From page 200... ...
The wind erosion estimates in the section on rangeland of this paper are very interesting. Like the USLE, the Wind Erosion Equation has certainly had minimal testing on western rangelands, with the exception of some work in Texas and New Mexico.
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From page 201... ...
1982. Effects of slope length and steepness on soil erosion from rangelands.
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From page 202... ...
1974. Applicability of the Universal Soil Loss Equation to semiarid rangeland conditions in the Southwest.
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From page 203... ...
1984. Prediction of sediment yield from southern plains grasslands with the modified Universal Soil Loss Equation.
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