Make sure you are clear about what you want to achieve with your shelter system. Is it just purely for shelter or will it also double as a timber lot or habitat for wildlife. Your objectives will influence the design of your shelter belt and the types of species you select.
A planned approach helps ensure that you get the maximum benefit for your dollar spent and you will end up with an asset that can improve the value of your property.
Download the Shelter Booklet - Protection from the Wind in Southland (2003)
Understanding shelter systems
The effectiveness of your shelter system is based around four main principles: orientation, permeability, length and height.
Windbreaks are best planted at right angles to the prevailing (damaging) winds. Usually in Southland North/South belts are evergreen and East/West belts are deciduous.
Shelter Belts should be designed to filter wind, not as complete wind barriers. This can be achieved by selecting the correct species for the site and spacing them at appropriate distances apart. Shelter systems with good permeability produce more even wind flows over a wide area while low permeability creates turbulence which is undesirable. Gaps in your shelter system from missing trees can also be a problem as they funnel wind through at excessive speed. It is therefore important to carry out regular maintenance and replace any missing trees as soon as possible.
Windbreaks should be as long as possible for the best protection as short plantings can loose their effectiveness when the wind slips around the ends. The rule of thumb is that an effective zone of shelter should extend 10-15 times the height of the windbreak.
The area protected is directly related to the height of the windbreak. The greater the height of the shelter, the greater the area of wind reduction is on both leeward and windward sides. Remember to plan your site carefully as trees can adversely impact on power lines, telephone cables, tile drains and cause shading on roads.
Establishment procedures are critical including ripping the ground, selecting the right species for the site and making sure they are planted correctly, controlling the weeds and ensuring the belt is well fenced and free from pest animals.
Windbreaks need regular maintenance including side trimming to maintain their porosity and stability. Naturally dense trees such as radiata pine and cypresses will require regular pruning and/or side trimming, while trees with an open canopy such as eucalyptus and poplars require less.
Tree trimming machines provide a fast and economical method of trimming side branches. By carrying out a regular side trimming the cost per kilometre is much less than if you leave it until branches are heavy and more difficult to remove. Fast growing species tend to crowd out the slower trees with overhanging branches and should be removed by side trimming or pruning to avoid damage to fences.
Well-designed and maintained belts should not need topping unless power lines are threatened. It is an expensive exercise and reduces the shelter effectiveness and timber value of the trees.
Fan pruning is a technique where all branches are trimmed except those pointing in the same direction as the row. It is an alternative to side trimming, which will reduce later maintenance but maintain shelter value.
Early pruning can save expensive machine trimming later and can be completed at any time during the year to fit in with the farm management programme. To maintain the best shelter, trees shouldn't be pruned any higher than the slowest growing species. Removing one whorl of branches each year up to a height of 6 metres can be easily handled.