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Wind Erosion

Wind erosion occurs when the force of the wind is sufficient to detach and carry soil particles. Windblown sands can damage crops or bury young plants, then blow up against fences, buildings and across roads, causing damage to infrastructure. The finer surface soil particles and organic matter that hold the bulk of the farm’s fertility can be blown for hundreds of kilometres, causing major dust storms.

The Universal Soil Loss Equation (USLE) for wind erosion demonstrates that changes in soil loss (as a function of soil erodability), wind speed, paddock roughness, paddock length and vegetation cover will influence the risk and extent of wind erosion.

The drier the soil and the higher the concentration of fine sand, the greater its susceptibility to wind erosion. Heavy clay soils may also be affected during very dry conditions if the structure has been damaged by stock, traffic or excessive cultivation. The presence of any vegetation, even dry grass, reduces the risk of wind erosion. However, damage may still occur during severe droughts, when pastures of crops fail or when the lack of follow-up rains leave ploughed paddocks or young crops exposed.

The ability of wind to dislodge and carry soil particles increases exponentially with wind speed. This means that halving the wind speed across an open paddock may be enough to eliminate wind erosion in many circumstances. Research on shelterbelt design shows that tall shelterbelts may be effective in halving wind speeds over a distance equal to about ten times their height.

Farmers are also able to reduce the extent of wind erosion by reducing the length of the paddock. Wind-blown sands bouncing along the surface induce a chain reaction causing more sand to break free, a process called saltation. Leaving a strip of ungrazed grass or a belt of trees between open paddocks, thereby reducing the wind run, can dramatically reduce the effect of saltation. Tree belts, if fenced to allow a thick understorey to develop, can be effective in catching the moving sands. The most appropriate paddock length will depend on the soil type and the likely wind strengths. By observing how soil erosion increases across their open paddocks, farmers may be able to judge the maximum width of their ploughed areas.

Belts of trees can therefore reduce wind erosion by reducing the wind speed and/or by reducing the length of the paddock. In cropping areas the design criteria for an effective erosion control shelterbelt might include:

• Tall trees to provide shelter over a long distance
• Aligning the belt perpendicular to the strong hot dry winds that cause erosion
• Having good foliage cover to ground level to reduce risk of wind tunnelling
• Fencing to prevent stock browsing and allowing grass and shrubs to bind the soil beneath the trees
• Locating gateways in sheltered corners to avoid wind tunnelling.

Trees for Wind Shelter

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