Recent gale force winds caused havoc to our lifestyles. They inflicted damage to infrastructure and many gardens. Effective windbreaks can greatly reduce the impact of gale force winds.
Having been a resident of the Southern Highlands for over thirty years I have become accustomed to the ferocity of winds experienced in our region. Traditionally they are at their worst during August. This year in July we experienced gale force winds that resulted in our region being declared a natural disaster zone. Hopefully with climate change affecting our weather these winds came early and during August we will experience mild conditions.
When I first moved onto my allotment it was virtually treeless and being on top of a ridge (with good views to the north and south) it constantly bore the brunt of gale force winds. The early years were tiring and demanding. Every year, damage would be inflicted upon the garden with the constant worry about wind damage to my propagation houses.
Today the scenario is quite different as wind protection from the south and the west has been achieved. Given the ferocity of this years wind, very little damage was experienced with no major concerns, even though the gales experienced were the worst for well over a decade. The worst of the winds roared above as birds and other inhabitants sheltered in the garden below.
Unfortunately, when planting windbreaks people often make mistakes through poor design and unsuitable species selection. The worst type of windbreak one could plant is a single row of a dense plant such as the Leylandii Cyprus. Windbreaks created with Leylandii or similar species obstruct the wind and then create turbulence. Very effective wind protection is achieved but for only a relatively short distance on the leeward side of the windbreak. Once out of this protected zone wind speeds and turbulence increase with intensified risk of damage to crops, gardens or structures.
A WELL-DESIGNED WINDBREAK SHOULD DIVERT AND MUFFLE THE WIND RATHER THAN OBSTRUCT IT.
For many reasons, the majority of windbreaks planted in the highlands are single row and dense with Leylandii being the most common species planted. These reasons seem to be based on myths, ignorance and prejudice.
So, what are the principles behind achieving effective windbreaks.
The efficiency and effectiveness of windbreaks depends upon the height of the windbreak, its width, density and porosity plus its orientation. Porosity would be considered the most influential factor determining the effectiveness of a windbreak. Porosity relates to the amount of air allowed to pass through or be muffled by the windbreak. The denser the vegetation a tree has the less effective it is as a windbreak.
Leylandii are extremely dense and may be effective as a hedge if clipped but would be determined as completely unsatisfactory as a windbreak when the science is considered.
The height of a windbreak determines how far wind protection extends from the windbreak. Wind velocity is generally reduced by up to 5 times the height of the windbreak upwind and up to 25 times the height downwind. As a general rule I allow for a distance of up to 15 times the height of the windbreak when planning the location of a windbreak.
If you are seeking advice as to design and species selection for a windbreak ensure the advice you act on is not driven by myth, ignorance or prejudice.