Overstory #32 - Multipurpose Windbreaks
Multipurpose Windbreak Design: Balancing Function and Yields
Windbreaks are rows of vegetation, usually trees, strategically placed to protect an area from winds. Although planting windbreaks is an investment that takes some land out of production, well-designed windbreaks have often been shown to protect the health and productivity of crops enough to make the overall return positive. Farmers in the tropics have looked at finding ways to increase the benefits further by creating multipurpose windbreaks. A multipurpose windbreak is designed to provide multiple functions and/or products, in addition to wind protection. Multiple produces from a windbreak can include yields such as fruit, timber, animal fodder, mulch, wildlife habitat, and other economic or farm products.
Adding multiple functions or products to a windbreak plan can make the installation and management more satisfying and economically viable for the farmer. The desire for additional yields must always be balanced by the need to maintain the integrity of the wind protection.
Multipurpose windbreaks require special care in planning and management to maintain the primary function of wind protection while maximizing secondary yields. When planning a multipurpose windbreak, is is best to factor in all the basic necessities for effective wind protection first. The basic design should include the appropriate orientation, placement, length, height, profile, number of rows, spacing, density, and continuity to provide effective protection. There are a number of excellent publications available in books, extension materials, and on the web that cover the specifics of form and position of effective windbreak design. Once the form and position are carefully determined, then multiple functions or products can be added.
General guidelines for multipurpose windbreak design:
- The species used should be selected first for their wind tolerance and appropriateness for the site (climate, soils, etc); the products should be a secondary consideration in selecting species.
- Windbreaks designed for multiple products should comprise of multiple rows. This affords some protection of the producing trees by the other trees in the windbreak. It also enables more flexibility in management and harvest of products without compromising wind protection by creating gaps.
- Trees yielding products such as fruit, food, fodder, or mulch should ideally be located in the interior or wind-sheltered rows of the windbreak, for maximum protection.
- A diversity of species should be used to allow for greater flexibility in management and for better resistance of the windbreak as a whole to damage from insects or disease.
Fruit or nut production
Incorporating fruit or nut-bearing species into the windbreak can provide increased family food or marketable produce. However, fruit trees battered by wind will usually have reduced yields resulting from poorer pollination, wind damage to flowers or young fruits, and reduced quality if the fruit falls to the ground or is bruised. In very windy areas, therefore, fruit from windbreaks is generally used just for family consumption.
To maintain the windbreak's primary function, wind-tolerant fruit tree species should be used. These should be integrated with other wind-tolerant species to form an effective windbreak. Also, keep in mind that fruit trees in a windbreak should be pruned only very sparingly, as pruning can greatly compromise wind resistance.
There are a number of things that can be done to maximize the secondary yield of fruit or nuts:
- If strong winds are seasonal, choose species that flower and bear in calmest months
- Plant fruit trees in the more sheltered areas of windbreak to maximize fruit production and quality
- Select trees which bear fruit on main branches, trunk, or interior of tree, rather than on outer branches (for example, fruits like jackfruit (Artocarpus heterophyllus) or jaboticaba (Myrciaria cauliflora).
- Know the cultural requirement of the fruit trees and care for them appropriately
- Irrigate if necessary
Example species that have been used for this purpose: coconut palm (Cocos sp.), dwarf Brazilian banana (Musa sp.), jackfruit (Artocarpus heterophyllus), mango (Mangifera indica), longan (Dimnocarpus longan), cashew (Anacardium occidentale), macadamia (Macadamia integrifolia), tamarind (tamarindus indica)
Since planting trees for a windbreak involves a long-term investment, the idea of including trees that will be harvested for timber one day appeals to many farmers.
The main drawback of having timber as a secondary yield from a windbreak is that wind stress or damage may compromise the timber tree's form or produce timber of poor quality. Also, since windbreak trees should be pruned only sparingly or not at all, the lack of pruning may reduce timber yields on certain species that require a lot of pruning for optimal timber production. Of all multipurpose uses of a windbreak, planning for timber harvest requires the most careful effort. Since entire trees will be removed, the planting, harvesting, and replanting must be coordinated to avoid creating gaps. Integrating timber trees with permanent rows of non-timber windbreak trees will help maintain the effectiveness of the windbreak.
To maximize secondary yield of timber, plan to selectively harvest. Some farmers plan to harvest entire rows on a rotational basis; others selectively harvest in a staggered pattern. Consultation with a professional forester is recommended.
Example species that have been used for this purpose: Eucalyptus dunnii (Dunn's white gum), Grevillea robusta (Silky oak), Pterocarpus indicus (Narra), and Azadirachta indica (Neem).
Mulch or fodder from nitrogen-fixing trees
Some farmers like to integrate nitrogen-fixing trees (NFTs) in a multi-row windbreak, and prune the NFTs regularly to provide a nutrient-rich mulch for crops, or a nutritious fodder to supplement the diet of farm animals. (For more on NFTs see Overstory #4.)
Although pruning should be avoided for most windbreak trees, the practice of cutting back NFTs and allowing them to resprout can be integrated with windbreak management. Pruned NFTs are much more susceptible to wind damage if they are allowed to regrow to a large size, but if they are cut regularly and the regrowth kept small they will be effective as a short row. To maintain the windbreak's primary function with this practice, it is essential to prune the NFTs regularly. Also, planting these species on the most sheltered side of the windbreak will help prevent problems and improve productivity.
Example species that have been used for this purpose: Leucaena leucocephala K636 (Giant leucaena), Sesbania sesban, Calliandra calothyrsus, and Gliricidia sepium.
The ability of windbreaks to provide wildlife habitat and corridors is one of the most documented, both in tropical and temperate areas. Many farmers enjoy providing important ecological benefits from their windbreak. Farmers that harbor wildlife may also enjoy other benefits, such as economic returns from wildlife or a more balanced pest/predator population in their crop area. (See Overstory #21 for more on wildlife in agroforestry; Overstory #27 for more on foster ecosystems.)
Keep in mind that providing wildlife habitat will harbor all kinds of animals, which may include rodents or other animals that are a problem for crops.
To maximize wildlife habitat in a windbreak:
- Create long, contiguous windbreaks that function as wildlife corridors
- Connect windbreaks to larger forest, wood lot, or wild areas if possible
- Plant known food/pollen source for target species
- Use a wide diversity of species
- Create an understory (shrubs and herbaceous plants, for shelter and foraging)
- Allow deadfall/old logs/snags for habitat (if not a safety hazard)
- Create a diversity of other niches for habitat (mulch, large trees, shrubs, etc.)
International Institute of Rural Reconstruction. Agroforestry Technology Information Kit, 1990. IIRR, Room 1270, 475 Riverside Dr., New York, NY 10115.
P. Ramachandran Nair, An Introduction to Agroforestry. 1993. Kluwer Academic Publisher. This comprehensive textbook bridges the gap between theoretical and practical knowledge in agroforestry.
D. Rockeleau, et al. Agroforestry in Dryland Africa. 1988. ICRAF, P.O. Box 30677, Nairobi, Kenya.
Agroforestry Information Service (AIS) for the Pacific Fact Sheet, "Windbreaks for the Pacific Islands," FACT Net (Farm, Community, and Tree Network)
Related Editions to The Overstory
- The Overstory #73--Buffers-Common Sense Conservation
- The Overstory #72--Microenvironments (Part 1)
- The Overstory #60- Trees as Noise Buffers
- The Overstory #45--Vegetative Erosion Barriers in Agroforestry
- The Overstory #38--Live Fences
- The Overstory #16--Multipurpose Trees