The effects of a medium-density shelter belt on orchard productivity
A good windbreak or shelter belt is a very profitable investment in relation to the productivity of an orchard in England. The main reason for this is that fruit set is significantly increased, particularly in years when during the blossom period the weather is cold and the wind is strong. This better fruit set is achieved as a result of the warmer microclimate amongst sheltered fruit trees.
The net effect of a better fruit set is even more important in years when blossom is not abundant. This can be caused by several factors. However in practice the main reason for scarcity of blossom is caused by over-cropping in the previous year. Another instance when the level of fruit set is of major importance, is when an April or May spring frost has killed off many blossoms. The remaining undamaged late-developing flowers will be the only ones left which can secure a crop of sufficient volume to be of commercial interest.
A very important factor is that the windbreak should be of medium density. For example, windbreaks of pine and/or fir trees are far too dense. These windbreaks cause strong air turbulence and therefore diminish the positive effects of a well-positioned windbreak. A windbreak of birch trees is ideal for an orchard. These trees by nature reduce the wind strength, instead of stopping the wind all together just behind the windbreak. Poplars, willows and alders have the disadvantage of blocking drainage systems in orchards. Moreover the vigour of these trees is often too great, thereby reducing the productivity of the fruit tree rows closest to the windbreak.
Effects of a windbreak over distance
The next point to consider is how far into the orchard does a windbreak make a difference to fruit tree cropping. Researchers have found that the optimum effect is found over an area 8 times the height of the windbreak. In other words, if the windbreak is 10 metres in height, then the area of orchard receiving the highest benefit is that within 80 metres from the windbreak. Beyond the 80 metre point there is still an effect, but at a reduced level. The strongest effect will be found in the area of 4 times the height of the windbreak.
Another point to be considered is that without insects, the quality of pollination is greatly reduced. Wind pollination is only effective when the climate conditions are such that the humidity of the air behind the windbreak is sufficiently high to make germination of the pollen possible. If the stigma is too dry then the pollen is unable to grow down the pollen tube of the flowers and therefore fertilization of the egg cell cannot take place. Without this fertilization process, no fruit growth can be achieved.
From the above statement it follows that everything must be done to attract beneficial insects, bumble bees and honey bees. The orchard environment has to be made attractive to insects so that they find it a suitable habitat in which to live throughout the year. This is particularly true for the period when blossom is over. A perfect combination capable of achieving this particular requirement is to plant a wild flower area in or around the orchard. The flowers in the wild flower mix are very important. Ideally there should be flowers open from April until November. In that way, beneficial insects and various predators will help create a natural balance, keeping the various species of pests under control. This will help the orchard to flourish in as natural an environment as possible.
Pollinating insects are more frequent visitors in well-protected orchards, particularly when temperatures are low during blossom time. Strong drying winds and salt-laden winds are often the cause of low fruit set and poor fruit growth. Also it has been established that fruit trees form fruit buds more easily if the area where the fruit trees are planted has the benefit of increased temperatures as a result of the wind reduction effect. Again, the best way to achieve this is by a row of birch trees, planted at the edge of the orchard.
Fruit size will also improve, as long as sufficient soil moisture is available.