A wind break or shelter belt is a carefully raised tree and shrub structure that can prevent the wind from beating on the land surface and blowing the soil
Shelter belt plantations raised over a period of time in Thoothukudi, Tamil Nadu. Photo: Govindaraju
This is the second of a two-part series. Read the first part
The Kuthiraimozhi Theri Reserved Forest in Tamil Nadu’s Thoothukudi district, is home to unique red sand dunes. The dunes have been formed due to deposition of red sand brought from the Nanguneri region in Tirunelveli district by southwest monsoon winds over many years.
These dunes are known in Tamil as ‘Theris’. Earnest attempts have been made for many decades to fix the great mass of shifting sands.
The idea is to save the cultivated lands on the eastern edge of the reserved forest from being destroyed by the sands blown over by fierce winds between May and August.
Initially, farmers were encouraged to plant the area with trees in conjunction with field crops wherever possible. Though the system was successful in afforesting the sandy areas, the results were disappointing due to deeper groundwater levels and shifting sands.
Now, the forest department is taking serious efforts to afforest the area through a scientific approach, with the aim of helping farmers.
The soil material on the surface of a theri is loosened due to the action of high velocity wind. The loosened soil particles are lifted and bounced along the surface of the ground by the turbulent wind.
The soil lifted in this way from one place gets deposited in another area. This kind of soil movement is known as wind erosion.
The best way of protecting the land against wind erosion is to maintain sufficient vegetative cover on the land. Apart from this, simultaneous action is needed to reduce the wind velocity and divert it away from the land surface.
This can be done by constructing a ‘wind break’ or ‘shelter belt’.
A ‘wind break’ is a narrow belt of trees planted in one or a number of rows in a field to provide protection from the wind. A ‘shelter belt’ consists of a wide belt of trees planted in several rows across the direction of the wind.
The main purpose of raising a wind break or shelter belt is to prevent the wind from beating on the land surface and blowing the soil.
A wind break or shelter belt may have any type of combination of trees. It should have dense foliage for providing protection both, near the ground surface and 30-40 feet above the ground level.
The effectiveness of the wind break depends upon the factors like density, height of trees, their deep rootedness and length.
The width of the field protected from wind hazards on the leeward (downwind) side of the wind break is approximately 15 to 20 times the height of the tree in the centre of the wind break. On the windward (upwind) side, about 5 to 10 times the height of the tallest tree is protected.
The spacing of the permanent wind break may be 20 to 30 times the height of the tallest tree, measured from centre to centre of the wind break.
The spacing depends upon the density and angle of the wind break to the direction of the hazardous wind.
Usually, the rows of a wind break may comprise shrubs, medium-sized deciduous trees and tall evergreen trees. In case of areas with high wind velocity, five or more rows are recommended.
Authorities in Kuthiraimozhi Theri RF have planned to plant seven rows in the area as it experiences high velocity winds for three to four months.
What constitutes it?
Tree species best suited for an area should be selected to be part of a wind break depending on the soil type, climate, rainfall and moisture availability.
The tallest trees should be in the middle row, medium-sized trees in the third row, short trees in the second row and shrubs in the first row or at the end row of the shelter belt.
Research findings have proved that the more or less conical cross section of the shelter belt provides the best protection from wind effects and also increases the zone of protection.
The spacing between two shelter belts can be 1,000 metres as the middle row shelter belt trees are expected to grow up to 30 metres. Hence, such a shelter belt can protect up to 30-35 times of land on the leeward side.
In addition, palmyrah nuts can be dibbled all along the boundary at a linear spacing of three metres. Two rows of pits of 30 cm x 30 cm x 30 cm size are to be kept ready all along the outer boundary before taking the nuts to the field.
The palmyrah nuts, with germinated radicles (the part of a plant embryo that develops into the primary root), are to be carefully (without causing any damage to the radicle) put in each pit (one in each pit) and covered by the soil gently. All the above works are to be completed before the onset of monsoon for better result.
For quite a considerable period of time, afforestation operations have been carried out in Kuthiraimozhi Theri RF and as a result of which, presently, various tree species have become established here. A few oasis are also occurring in the low lying marshy pockets where trees such as the screw-pine and Arjun occur.
It now remains to be seen whether the march of the red dunes can be stopped.
Views expressed are the author’s own and don’t necessarily reflect those of Down To Earth
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