WIND BREAKS AND SHELTERBELTS

Windbreaks are such structures which break the wind-flow and reduce wind speed while shelterbelts are rows of trees or shrubs planted for protection of crop against wind. They provide a protective shelter against wind and suitable habitat for birds and honeybees as well as produce cattle feed and fuel wood. In the wind erosion areas, windbreaks and shelterbelts are to be planted. They prevent the soil erosion, arrest the desert and protect the agricultural and residential lands from dust-storms. A row of trees and shrubs planted across the winds-direction is the most effective. It reduces the wind speed up to 60-80% on leeward side. The height of tall tree and length of wind break determine the extent of protection provided to soil.  Windbreaks and shelterbelts provide the protective shelter against desiccating winds to extent of 5-10 times the height of the tall tree on windward side and up to 30 times on leeward side. For example a 10-11 meter tall windbreak when encountered by 45-50 km /hr wind, it reduces on windward side to 20-30 km /hr and to 10 km / hr on just leeward side.

The windbreak reduces the wind speed on the leeward side at 200 m away up to 20 % only and in the area as at 300m away, there is no effect at all. Therefore at an interval of 300m, such windbreaks should be repeated.

To control wind erosion, the capacity of shelterbelt depends upon the speed and direction of wind. In case of high wind speed, the protective area is reduced and in such areas, the interval between two shelterbelts is to be reduced. To counter winds direction, it is necessary to be long length of windbreak so that wind blows across the wind break. Depending upon the porosity of shelterbelt, certain amount of wind passes through it and some deflects & crosses over it. Thus, it does not produce turbulence of air.

Reducing the wind speed reduces the evaporation losses and makes available more water to crops. According to planting pattern of trees and shrubs as shelterbelt, the grasses and shrubs are planted on the outer rows which train the wind to rise much above the ground surface. The inner rows are of small trees which further raise the wind level.

The beneficial effects of the shelterbelts are more clearly seen in drought areas. In such areas windbreaks of 3-7 rows and 15-30 m wide are more effective. It modifies the micro-climate favourable for crop production and shelters for birds, honeybees and pet animals. The windbreaks and shelterbelts should be formed in North-West direction. These shall secure the crops and livestock against cold wave also.