Designing windbreaks

Designing an effective windbreak will help you get the greatest possible benefit from the shelter it provides. Every property has different topography and production requirements, so each windbreak needs to have varying characteristics. Despite this , there are some rules of thumb that can be applied when designing windbreaks for our region.

Much of our region is treeless or has only scattered trees, so often farms are adversely affected by lack of shelter. We all know the pleasure we get from the shade of trees on hot summer days. Animals also suffer greatly from exposure to heat and wind and it's common to see them huddling behind trees, power poles and anything they can get shelter from. There is much evidence showing the economic benefits gained by providing shade and shelter for stock. The mortality rate of young lambs is much higher on country lacking shelter from cold wind and rain. Shelter provided by windbreaks also has a marked effect on the growth of grass. Although there is a loss of fodder directly within the root zone of trees, when the increased growth in the area protected by the windbreak is taken into account, there is a significant net gain in production.

Windbreaks should ideally be oriented so that they run at right angles to the wind. In this region wind is mostly from the West or North West so breaks running from North to South give the greatest benefit. In winter we get cold Antarctic blasts from the South which are dangerous to sheep and small livestock, particularly during lambing. Some protection from these winds can be advantageous.

Generally, the taller the windbreak the greater a distance from the belt that a reduction of wind occurs. A windbreak usually reduces the wind close to the ground for a distance on the leeward side equivalent to around 25 times the height of the windbreak. Many factors will determine how the wind acts as it passes over a windbreak. Dense plantings often give a very calm area directly behind the break, but can produce high turbulence for the remaining sheltered area. In areas requiring crops this can be detrimental, but for shelter for animals this can be advantageous. If you allow some permeability the area of reduced wind speed extends much further beyond the belt.
The shape, width , length and species makeup of the break also greatly affects its success. To be effective, breaks need to be of reasonable length. The most desirable cross sectional profile of a windbreak is one with ascending heights of vegetation creating a ramp for the wind to climb. This profile offers less resistance to the wind than a narrow row of trees which creates a vertical wall. Windbreaks with no density near the ground can cause winds to increase as they get funneled underneath. This may be caused by the lower branches of trees being shaded and dying or being pruned. Planting shrubs along the windward side of the breaks is one effective way of ensuring wind does not get funneled underneath it.

There is an enormous range of species to choose from when deciding what to grow in your windbreak and each has it's own advantages and disadvantages to weigh up. The biggest advantage of using native vegetation rather than exotic is that it has significantly less chance of being destroyed by fire. Most native species have evolved mechanisms enabling them to survive fires. If you require further advise on how to establish a windbreak that best suits your requirements, we are happy to assist.