Design:
There are several key elements to effective shelterbelt design. The elements that need to be considered are height, length, density, location, number of rows and the species to be used. It is important to maximize the height of a shelterbelt, as its height will determine the area over which the windbreak has a positive impact. Using the tallest suitable shelter species in at least one row of the belt will increase the eventual area over which a shelterbelt is effective. The species used for the taller row can be fast growing, to achieve maximum height rapidly.
Density is the proportion of solid material, such as foliage, branches etc. within a shelterbelt. Density can affect the extent and level of shelter provided. Wind turbulence is generally reduced with lower degrees of density. A high-density shelterbelt will provide a higher level of shelter over a shorter distance than a medium or low-density belt. Therefore very dense windbreaks may be used where a high level of shelter is required over a short distance. The design should aim for a medium density belt using shrubs and ground cover species as well as taller species. A shelterbelt consisting of 2- 4 rows using taller species that provide the benefits of a tall belt combined with shrub species that provide shelter lower down would offer an overall uniform density.
Field shelterbelts are used to shelter agricultural fields, while farmstead shelterbelts are planted around farmyards or livestock facilities. Trees and shrubs are also planted in blocks for woodlots or farm habitat. Field shelterbelts decrease wind erosion by reducing wind speeds for distances up to 20 times the height of the trees. They also trap snow for increased spring soil moisture, reduce wind damage to crops, and decrease evaporation of soil moisture and store carbon. Shelterbelts are most effective when planted across the prevailing wind direction. For increased sheltering effects, the shelterbelts can be spaced more closely together; for maximum wind erosion control, the rows should be spaced between 2 to 4 meters apart to allow the plants to grow relatively unrestricted.When considering shelterbelt planting, three zones can be recognized: the windward zone (from which the wind blows); the leeward zone (on the side where the wind passes); and the protected zone (zone in which the effect of the windbreak or shelterbelt is felt) (Fig.7).