Shelterbelt Size
The size of a shelterbelt depends on what you need it for. If it is being used to protect fruit trees or crops, it should be twice the height of those plants, but shouldn’t block them from the sunlight.
The shelterbelt should be as long as practically possible, as wind will flow around the ends. A tall, skinny shelterbelt will block little or no wind.
Sometimes it may not be practical to plant a tall shelterbelt. A low shelter is better than nothing; it will actually slow the wind for up to ten times the height of the shelterbelt!
Shelterbelt Position
It goes without saying that shelter belts should be planted at right angles to the prevailing wind. However, you also need to take into consideration the topography of your property. It can be beneficial to plant on slopes or near stream banks to stop erosion.
Also, be careful not to block your view! Many a pristine landscape has been ruined by careless placement of tall trees.
Types of Shelterbelts
Shelterbelts consist of one or more rows of plants. They can have one, two or many different plant species. In any case, they need to be somewhat permeable, as a shelter that completely blocks the wind will cause turbulence in the air, and will be less effective than one that actually allows a little wind through.
Tall shelterbelts are often planted using fast-growing trees and can be pruned into shape. If you want to use a slower growing tree with a longer life expectancy, or if you want to use native trees, it pays to plant lower, shrubby plants first that will shelter the young trees as they grow.
Multiple plant types can create an effective and visually pleasing shelterbelt, but be careful not to overplant, as this can result in the shelter not being permeable to wind.
Species of Plant
This will depend largely on the climate and soil type of your property. A good rule of thumb is to look around for what grows naturally in the area.
Landscapers can help you to plan your shelterbelt and choose what kinds of plants to use.
Radiata pine is one of the most common trees used for shelterbelts in New Zealand because it grows quickly and responds well to pruning. However, fallen pine needles will cause acidity in the earth, and you won’t be able to grow any other plants underneath. Macrocarpa and poplars are also common choices.
Eucalypts have been used on many farms. They have few low-hanging branches, so they can work well in conjunction with other, smaller trees.
Flax is a great, hardy option for short windbreaks, or as shelter for young trees.
Any number of native trees can be used, including totara, manuka, karo and even rimu.
Deciduous trees can also be used if you want to allow sunlight to get through in the winter.
Whichever plant species you choose, make sure that it is wind tolerant, hardy, and responsive to trimming.
Shelterbelt Pruning
Depending on the species of tree, it is highly recommended that you prune your shelterbelt to stop it from growing too thick and completely blocking the wind. This is best done regularly in the first few years of growth to make management easier later on.
Some species of tree will respond to fan pruning, which involves trimming off any branches which grow outwards from the shelter belt, leaving only those that grow parallel. This creates a strong visual effect, and allows wind permeability.
