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Strong winds can wreak havoc on crops, pastures, vineyards and orchards, causing breakages and fruit fall and having a sandblasting effect.

For instance, property owners on the Swan Coastal Plain predominantly face strong easterly winds in the morning that swing to the south-west in the afternoon. During winter, damaging winds can prevail from the north-west. Windbreaks can be established to provide protection against these winds.

Windbreaks work by reducing wind speed and turbulence downwind of the shelter itself. They should be permeable and aim to filter the wind, not block it out completely. The most cost-effective windbreaks are trees, which can also offer additional benefits to the property. They can help to prevent soil erosion, improve plant growth by reducing moisture stress, protect plants from wind damage, provide shade and shelter for livestock, lower the water table in 'boggy' areas, increase biodiversity and reduce evaporation from farm dams.

The benefits of a well-designed windbreak generally outweigh the possible disadvantages. One disadvantage of planting windbreaks is the perceived loss of land. Money and time to plant the trees and the ongoing maintenance (pruning, irrigation, fencing and fertilising) also need to be considered when planning a windbreak.

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To ensure a windbreak achieves what you want it to, it needs to be carefully designed, _see figure 1 below _.

Windbreak design

In terms of orientation, windbreaks should be at right angles to the prevailing wind direction. For properties on the Swan Coastal Plain, a windbreak running north-north-west to south-south-east will give the best protection without causing excessive winter shade. Always check your farm plan for any access roads or other structures that may be impacted.

An effective windbreak will filter the wind, not stop it from passing through. Ideally, permeability should be about 50 per cent. Gaps should be minimised in the windbreak to prevent wind tunnels that may cause direct damage to plants on the other side.

Windbreaks work best when they comprise several rows of staggered trees and shrubs. This allows the trunks of one row to be aligned with gaps in the next row. Planting at least three tree rows offers protection against gaps from seedling or mature plant deaths. If a tree dies another should be planted in its place.

Shrubs are best planted on the outside (windward) with taller trees on the inside of the windbreak. Plant rows about 3-4m apart. Most trees and shrubs should be planted in a line about 3-5m apart (wider gap between trees, lesser gap between shrubs). If planting only one or two-row windbreaks is unavoidable, reduce the spacing between trees to achieve quicker closure of the canopy and to insure against gaps.

Where an access track or gate is needed, plant some shrubs right up to the gate/track to help prevent the wind from accelerating through the space. An additional short windbreak at least twice the length of the gap to the windward side of the access gap can help.

The higher a windbreak, the larger the area it will protect. However, height is best limited to 10m to prevent excessive shading of the adjacent area. Windbreaks offer wind protection to a distance of about 10 times their height. For example, a 5m high windbreak will give protection for about 50m downwind from the windbreak. Protection is greatest at ground level, however, so protection of orchards, grapevines and other taller crops will be less because of their height above the ground surface.

The length of the windbreak needs to be a minimum of 15-20 times the height of the trees, otherwise the wind will be deflected around the ends and lose effectiveness. Therefore, a 5m windbreak should be 75-100m long.

To reduce shading and competition from tree roots, windbreaks should be planted at least 10m from any crop. Allow a greater buffer area if tall windbreak species are being used. Sufficient room should be left to allow ripping of the tree roots, vehicle access and turning space. A greater distance between crop and windbreak is required when trees are planted to the north of the cropping area, so as to minimise shading in winter.

Choosing suitable species

A wide range of species are available for windbreaks. Choose species that are well adapted to the site conditions. By using plants local to your area, you'll have higher plant survival rate because they have adapted to the site conditions over time and generally do not have any pests or diseases. Choosing the wrong species for a soil type and rainfall area can end in poor growth and premature deaths. _See list, below left. _

When choosing species, ensure you match tree species to your soil type and consider the mature height and lateral root growth. In addition, take into account water requirements and growth rate and choose species that retain foliage close to ground level. Also consider a combination of species, which is recommended to reduce gaps and provide biodiversity.

If suitable for your farm, deciduous trees can be considered for frost-susceptible locations to prevent cold air being trapped by the windbreak. Always check the potential of any species you are considering becoming a weed on your property.

Establishing a windbreak

Prepare the ground first. Nearly all soils benefit from ripping, because it breaks up compacted soils, such as those found on properties with a history of grazing. It's best to rip deep in late summer/early autumn when the soil is dry, to a depth of 50-80cm.

Mounding may be necessary in waterlogged areas. Mounds should be 20-30cm high by 1m wide and done on the contour.

Before the trees are planted, control weeds to a distance of 1m outside of the proposed tree row/s by cultivation or with herbicides. A non-residual herbicide such as glyphosate can be used. For more effective weed control, use a residual, pre-emergent herbicide such as Simazine (only if no run-off can occur) and wait at least two weeks before planting the trees.

Consider irrigation and fertiliser next. If you use local species and plant early after the break of season, the trees should be able to get established before the dry, hot summer. However, nearly all species will benefit from being watered once a week during the first two to three summers if possible. Irrigation is also likely to promote a sustained growth rate and reduce root invasion into any irrigated production area.

Fertiliser requirements will depend on the species but most trees (including natives) will benefit and grow more quickly with some additional nutrients. Check with your tree supplier for recommendations.

Using local or native species will minimise pest and disease attack. Rabbits, kangaroos and ducks can find seedlings tasty, so try to control pests before planting or consider using tree guards specific to the pest/s if possible.

During establishment of a windbreak, it is desirable to exclude stock so that the trees can reach their maximum height rapidly. Temporary (electric tape) or permanent fencing could be erected. Consider allowing stock to access the shade offered by the windbreak once the understorey is well developed but remove them if damage and gaps in the trees or shrubs become apparent.

Windbreaks can be a great addition to any property. They can help prevent soil erosion, protect plants from wind damage, provide shelter for livestock, increase biodiversity and reduce evaporation from dams. However, it is vital that you take the time to plan. Consider purpose, location, design and species so that you get it right the first time and enjoy the many benefits windbreaks can provide your property.

For information, contact the Small Landholder Information Service on 9733 7777

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