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11111m1i1~1~11r~~~~r~11~r11m1111113 0307 00007 6102 84078 This document is made available electronically by the Minnesota Legislative Reference Library as part of an ongoing digital archiving project. http://www.leg.state.mn.us/lrl/lrl.asp (Funding for document digitization was provided, in part, by a grant from the Minnesota Historical & Cultural Heritage Program.) APPENDIX OFF-ROAD VEHICLE USE IN MINNESOTA (pursuant to Laws of Minnesota. 1983, Ch.~ Sec. 56) ot 1111' o_artment of Natural Resources TL. 235~6 . 033 appendix APPENDIX I . OFF-ROAD VEHICLE LITERATURE REVIEW by Ju l i e Ste ph ens and Su sa n Bl a ch man University of Minnesota Center for Urban and Regional Affairs 21 November 1983 I. Effects on the Env ir oo men t A. Soils Little research has been conducted on the effects of recreational ORVs on soils. However, many studies evaluating the impacts of agricultural practices in soi 1 s have been done and these findings appear to correspond closely with the possible influences of ORV use on soils. Soil compaction and erosion are the major consequences of ORV use. Conpaction, defined as "a change in volume for a given mass of soil due to mechanical or natural sources" (Barnes 1971) causes changes not only in the physical structure of soils but also in their chemical characteristics. A reorientation of the particles takes place, pranpting soils to behave more as a plastic than as an elastic material • The amount of liquid greatly influences the compaction process and has both direct and indire·ct bearing on the changes caused by compaction in the bulk dmsity, strength, temperature, air supply and nutrients of the soils. Finely textured soils such as clay hold more water than other soil types and are therefore less susceptible to canpaction (Barnes 1971). Similarly, soils with high porosity are more compressible than those with low porosity. Bulk density and solid strength increase with canpaction which in turn decreases soil permeab i 1i ty to water thereby reducing the soi 1 1 s water-holding capacizy. Thus, there is an increase in water runoff which can influence soil erosion. Webb (1978) noted in his study of a California state ORV area that gravelly sandy loam, coarse sandy loam, sandy loam and clay soils all experienced increas~d soil strength and bulk density with a decrease in soi 1 moisture. · Clay loam al so increased in soi 1 strength but had variably increased bulk density and no decline in soil moisture. Liddle (1978), in his study of vehicle tracks and pedestrian paths on sand dunes in North Wales, found that bulk density and p01etration resistance are 1in early related to the log of the number of passages of a car and of walkers. Cars cause a ll percent greater increase in bulk density and a 100 percent greater increase in soi 1 strength than do walkers. Also, water contmt of canpressed soil in dry areas was greater than the adjacent undisturbed soi 1. Arndt (1966) noted a four-fa ld difference in soil strength between crop rows and traffic rows, illustrating the differences that bulk d01sity has on soil strength. Similarly, Voorhees (1978) found that after 5 to 6 tractor passes bulk density increased by 20 percent in the O - 15 cm layer and 10 percmt in the 15 - l> cm layer with soil strength/resistance in.creased as much as 400 percent, significant 0-60 cm. In addition to density and strength changes Webb (1978) noted increases in diurnal temperature fluctuations, a loss of organic matter and a decrease of soil nutrients in all 6 of the soils he studied. He observed a loss of vegetative cover due to compaction (and erosion) \\fiich decreased the thermal insulation of the soils. Soil moisture was thereby lost which in turn caused a rise in soil -1- ·temperatures. The decline in organic materials reduced the supply and availability of nutrients as well as lowered the soil's water-holding capacity. Liddle (1975) however, suggests that canpaction is likely to increase the build-up of organic material. Barnes (1971) found that increases in both soil density and water content cause rises in thermal conciJctiv ity, di ffus ity, and capacity. Similarly, he found that a decrease in the diffusion of nutrients occurs l/kten there is a decrease in soil water content due to compaction.. However, if water entry remains satisfactory and proper use of fertilizers are incorporata:I, moderate canpaction is not necessarily detrimaital to nutrient flow and plant growth. Anaerobic conditions such as restricted oxygen transfer to microorganisms and roots due to reduced or destroyed pore spaces was noted by Barnes (1971) and Liddle (1975). Canpaction may also alter the gaseous composition of soils if air parasites are reduced s i gn i f i can t 1y • Voorhees (1978) found wheel-induced compaction to be more persistent in individual soil structure units (clods) than in bulk soil. Wheel-tracked clods were more than 300% more resistant to crushing and had larger aggregate diameters., Al though high-clod density can cause seedbed preparation problems bo.th Arndt (1966) and Voorhees ( 19 78) suggest that high-clad density can offer eras ion contra 1 balefits. Deliberate pre-cultivation compaction is common in agriculture. Another form of soil disturbance closely tied with compaction is shear damage which may, in fact, be more damaging than canpaction. Slippage between the strata or particles in planes parallel to the soil surface occurs. Harrison (1976) and Wilshire (1979) note that tire-spinning, associated with off-road vehicles, causes both canpaction and shear damage. "Paddle" tires used for hillclirrbing in soft soil displace huge amounts of soil, are responsible for quarrying effects (excavation of underlying rock) and cause rapid den uda ti on of ORV are as (W i1 sh ire 19 79 ) • The s k id - steer des i gn steering method associated with all six-wheel ATVs causes more ground disturbance than any other steering method. Al though the large balloon ATV tire with its low pressure minimizes canpaction, shear is increased as tire pressure is decreased. In other words, the narrower the tire the less the shear damage but the greater the compaction stress. Several approaches toward preventing or minimizing soi 1 compa·ction and shear damage have been presented in the literature. Most researchers advocate managemait techniques that limit ORV access to non-fragile soils. Least-sensitive soil areas should be designated, use should be restricted to prepared trails, and an awareness of seasonal variation in sens it iv ity to use should be maintained (Wilshire 1979). Harrison (1976) offers several suggestions: do not run back and forth in the same tracks, avoid l/kteen spin, use large radius turns (less skid) and maintain tire pressures at reconmaided figures (pressures should be increased, however, on dry, fragile soi 1s). He advocates better operator instruction and training to avoid soil damage. Barnes (1971) notes that because many of the -2- undesirable features of canpacted soils are hi9'11Y conditioned by their water content, water managemB'lt on compacted_ and high-clay soi 1s is very important • Bes ides the effects of ORVs on soi 1 compaction and shear damage, soi 1 erosion and sedimentation are other major consequences of ORV use. In fact, the soils property changes resulting from compaction contribute to accelerated erosion (Webb 1978). Three types of erosion often result from ORV use: l) direct mechanical erosion by the vehicles themselves, 2) water erosion of denuded areas,· and 3) wind erosioo of surfaces dest~bilized by ORVs (Wilshire 1979). In his study of 500 ORV sites in 7 western states, Wilshire found numerous cases of extreme erosion problems. In 3 years of motorcycle use at one site, the runoff exceeded that of the control area by a facto·r of 8, and sedimait yield was 15,000 tons/km2/year in canpar i son to an amount too sma 11 to measure. Similarly, 7 years after closure the eros i oo rates at another site were st i 11 50 times the natural rate. Webb (19 78) found erosion severe at a California state ORV area particularly in coarse-grained soils on steep slopes. In addition to the sites directly affected by ORVs, adjacent areas are also impacted by erosion and sedimaitation due to excessive runoff /flooding, headwater gu 11 ying, s il tati on of lakes, lowered water tables, lowered water quality, and wind action (Wilshire 1979, Hi 11 1948). Various managemEflt tools and techniques to prevent or minimize erosion problems are ·available. The lhiversal Soil Loss Equation (USLE) has been widely advocated to aid in predicting erosion rates at a site under a given set of conditions (USDA Soil Conservation Service 19 77, Wis chmei r 19 74 & 19 76, Meyer 19 75, Webb 19 78). Although originally developed to predict losses from agricultural lands induced by rainfall, the USLE can be applied to ORV areas. The factors included in the equation are rainfall, erosion potential, soil erodibility, slope steepness, slope length, cropping/vegetation managanent, and erosion control practices. Gie source (USDA 1977) notes that the effect of snowmelt can al so be incorporated into the equation in areas where the contribution is significant. Most of the factors can then be manipulated to determine trail sites that will erode at a minimum rate. Similarly, al ternatiye erosion control programs at a given site can be compared and evaluated for their effectiveness in minimizing erosion. Soils with severe erosion potentials can and should be avoided with guidance from the information provided fr an the USLE. The USLE was designed to predict long-term average soi 1 loss es for specific carbinations of physical and managanent conditions.