Shelter-belt: Overview and Characteristics
A shelter-belt is a system of trees planted in rows, typically at right angles to the prevailing wind direction, designed to provide protection against wind and its associated negative impacts. These protective barriers are especially important in regions prone to wind erosion, high winds, or desertification. Shelter-belts are commonly used to:
- Deflect Air Currents: By creating a physical barrier, shelter-belts deflect the wind, reducing its impact on the land.
- Reduce Wind Velocity: Shelter-belts slow down the speed of the wind, which can otherwise erode soil, damage crops, and create a harsh environment.
- Protect Leeward Areas from Wind Erosion: The protection offered by shelter-belts reduces the amount of soil erosion in the areas that are sheltered from the wind.
- Mitigate the Desiccating Effects of Hot Winds: In arid and semi-arid areas, shelter-belts can help reduce moisture loss caused by hot winds, thereby protecting crops and vegetation.
- Provide Resources: Shelter-belts not only serve a protective function but also provide additional benefits such as food, fodder, and timber.
Key Characteristics of Shelter-belts:
Shape and Composition:
- Shelter-belts typically have a triangular shape, which helps in maximizing the wind deflection and ensuring efficient protection across a wider area.
- To achieve this triangular shape, taller trees are planted at the center of the belt, with progressively shorter trees and shrubs at the edges.
Density and Width:
- The ideal width of a shelter-belt in Indian conditions is usually up to 50 meters. This width is considered optimal as it allows for sufficient wind penetration to ensure effective protection without diminishing the effectiveness on the leeward side too much.
- If the shelter-belt is too dense, wind penetration becomes extremely limited, which can cause the shelter to be less effective as it creates a sharp wind gradient on the leeward side.
Height and Spacing:
- The ratio of height to width of the shelter-belt should typically be 1:10, though this ratio can vary depending on local conditions such as wind velocity, terrain, and the type of protection needed.
- Spacing between trees in the shelter-belt should allow enough room for growth while ensuring effective windbreak. The trees are typically spaced at regular intervals to prevent overcrowding but maintain a dense enough cover for wind reduction.
Orientation:
- The orientation of a shelter-belt depends directly on the direction and velocity of the prevailing wind. If the wind direction changes frequently, shelter-belts may be planted in quadrangular arrangements to provide protection from different directions of wind.
- Shelter-belts are often designed with flexibility in mind to adapt to local wind patterns and maximize their effectiveness.
Length:
- The length of a shelter-belt is a critical factor for effectiveness. The minimum length should be about 25 times its height to ensure adequate protection across a large area. A longer shelter-belt will provide more continuous protection, especially in areas with varying wind conditions.
Choice of Species for Shelter-belts:
The effectiveness of a shelter-belt largely depends on the choice of species planted. A mixture of grasses, shrubs, and trees is typically used to create a multi-layered system that can provide maximum protection. The specific species selected will depend on local conditions such as soil type, climate, and the need for additional benefits (such as fodder or timber).
- Grasses:
Grasses play an important role in providing ground cover and preventing soil erosion. They also help in reducing the velocity of wind near the ground.
- Saccharum spontaneum (Wild sugarcane)
- S. munja (Munja grass)
- Panicum antidotale (Blue panic grass)
- Cenchrus species (Buffalo grass)
- Shrubs:
Shrubs add another layer to the shelter-belt, acting as a buffer and providing additional protection from wind. They also help in increasing biodiversity and supporting wildlife.
- Calotropis procera (Sodom apple)
- Clerodendron phlomoides (Glory tree)
- Cassia auriculata (Tara tree)
- Dodonaea viscosa (Hop bush)
- Trees:
The trees form the primary windbreak and provide long-term protection. They should be fast-growing, drought-resistant, and capable of withstanding strong winds. The species chosen for the tree layer should also have multiple uses such as timber, fodder, or soil conservation benefits.
- Acacia arabica (Indian gum arabic tree)
- A. leucopholea (White acacia)
- Dalbergia sissoo (Indian rosewood)
- Lannea coromandelica (Indian laurel)
- Eucalyptus species (Eucalyptus trees)
- Tamarix articulata (Tamarisk)
- Parkinsonia aculeata (Jerusalem thorn)
- Prosopis juliflora (Mesquite)
- P. spicigera (Indian mesquite)
- Casuarina equisetifolia (Australian pine
