Vigorous windbreak

Technical articles - Soil preservation

Hedge Agroforestry Water management Crop protection

Brise vent sur le périmètre irrigué de Daibéri, Tillabéri-Niger (Photo A. Sabra 2010).

Windbreaks are linear structures, most often multi-layered and living, composed mainly of woody species and sometimes herbaceous plants. They are arranged in such a way that they protect cultivated areas, pastures, homes, or infrastructures (roads, water points, schools) from the harmful effects of prevailing winds.

A windbreak separates two zones: the "windward" zone, located on the side from which the wind blows, and the "leeward" zone, situated on the side where the wind moves towards.

Objectives

• Reduce wind speed on both sides: windward and leeward, without increasing turbulence.
• Reduce or eliminate wind erosion within the protected area.
• Trap the solid load of the wind, thus limiting soil (and often fertility) transfers from one zone to another.
• Significantly reduce potential evapotranspiration (PET).
• Help improve crop yields in the protected zone.

The protected area behind the windbreak is greater on the leeward side than on the windward side. Downwind, protection extends over 15 times the height of the windbreak, and on the windward side, it’s 5 times the height of the windbreak.

Context / Environmental Conditions: Windbreaks can be established on all types of land and soil and are used in all climates, particularly in Sahelian and Sudanian regions. Windbreaks can be particularly installed to protect irrigated perimeters, rainfed agricultural lands, and fixed dunes.

Implementation Steps

• Determine the area to be protected (length and width of the area).
• Choose woody species according to the height of the future windbreak. If H is the height of the future windbreak, it will protect the leeward zone over a distance of 15 times H and the windward zone over a distance of 5 times H.
• Acquire the selected woody species.
• Establish the type of windbreak.

Technical Characteristics

• Orientation of the windbreak: Perpendicular to the direction of prevailing winds.
• Height: According to the relationship: protected distance = 10 to 15 times the height of the windbreak.
• Length of the protected area: 11-12 times the height of the future windbreak (to avoid turbulence on the sides).
• Permeability: Estimated at 50% void for optimal windbreak effect.
• Linear planting arranged in 4 rows (of trees and shrubs) in staggered formation over a strip 12 m wide.
• Spacing between trees and shrubs depends on the species and should match the canopy diameter of the chosen species for the windbreak.
• Density: Depends on the species. For woody plants with a canopy diameter of 4 m, 250 plants per km per row are required, or 1,000 trees for the 4 rows of the windbreak.
• Planting hole dimensions: 0.40 m x 0.40 m x 0.40 m.

Characteristics of Woody Species

• Tall species: Neem (Azadirachta indica), eucalyptus (Eucalyptus camaldulensis), acacia (Acacia tortilis ssp raddiana), Siamese cassia (Cassia siamea).
• Shrubby species: Cashew (Anacardium occidentale), false mimosa (Leucaena leucocephala), Bauhinia rufescens, Acacia holosericea, Mauritius jujube (Ziziphus mauritiana), moringa (Moringa oleifera), siwak (Salvadora persica), Euphorbia balsamifera, Acacia senegal, Acacia laeta, etc.

Community Training and Worksite Organization

The beneficiary communities should be trained to follow the technical standards for windbreaks. During the establishment of windbreaks, a reminder of the worksite organization should be given to the entire team.

The organization includes: a site manager, a supervisor or pointer, a team of tracers (usually 8 members), and other participants organized into teams of 10 to 20 people per hectare. Each team is led by a team leader. The supervisor or pointer oversees the teams and ensures compliance with the technical standards for the windbreak construction.

Materials

• Shovels.
• Picks.
• Ropes.
• Measuring tapes.
• Machetes.
• Pruning shears.
• Personal protective equipment (PPE): boots, gloves, and face masks.

Management, Ownership, and Sustainability Measures

• Maintain the windbreaks.
• Set up a site management committee.
• Develop a windbreak management plan.
• Sign a local agreement between the Ministry of the Environment and the site operator or the group of site operators.

Advantages and Disadvantages/Constraints

Advantages

• Effective and durable protection against wind.
• Creation of a favorable microclimate.
• Increase in agro-sylvo-pastoral production.
• Increase in the availability of wood, fruit, medicine, and other ecosystem services.
• Technique easy to master in rural areas.
• Carbon sequestration.

Disadvantages/Constraints

• Requirement for protection of planted trees from animals.
• Habitat for crop predators.
• Negative shading effect on some farmed areas.
• Occupies space.

Costs of the technique per hectare

Categories	Unit	Quantity	Unit price (FCFA)	Amount (FCFA)
Hole digging	Unit	1000	100	100 000
Small equipment kit (shovel, pickaxe, rope, measuring tape, machete/pruning shears, etc.)	Flat Rate1*	1	3 500	3 500
Personal protective equipment (PPE): boots, face masks, and gloves	Flat Rate2*	1	300	300
Forest plants	Plants	1 000	100	100 000
Transportation	Plants	1 000	30	30 000
Planting	Plants	1 000	30	30 000
Replanting in the second year (purchase of plants, transportation, and planting)	Man/D	333	160	53 280
Guarding/security (for 3 years)	Man/Year	3	20 000	60 000
Supervision	Man/Day	1	7 000	7 000
Total investment				384 080
Guarding/security (for 3 years)	Man/Year	3	20 000	60 000
Total investment				564 720

The costs must be contextualized based on local realities:

1*: This cost is calculated based on a team of 60 people using a set of tools (shovels, pickaxes, daba [hoe], water level cord, etc.) costing 350,000 FCFA and amortized over 100 hectares in one year.

2*: This cost is calculated based on a team of 60 people using Personal Protective Equipment (PPE) (gloves, boots, masks, etc.) costing 30,000 FCFA and amortized over 100 hectares in one year.

Lifespan

A windbreak can last 30 years or more if well managed.

Sources

• Brise vent vif - Niger GDTE.
• Ministry of Agricultural Development (MDA), 2006. Technical Guidebook on Natural Resource Management and Agro-Sylvo-Pastoral Production, Niamey, Niger, Community Action Program (PAC). 270 p.
• Mille, G., & Louppe, D. 2015. Memento of the Tropical Forester. Versailles, France, Quae Editions. 1203 p. Centre technique forestier tropical (CTFT), 1989. Memento of the Forester. 1257 p.

Cette page a été rédigée en partenariat avec le projet Urbane et grâce au soutien financier de l'Union Européenne.