Windbreaks
Windbreaks are single or multiple rows of trees planted along windward field boundaries. By slowing wind speeds, windbreaks help conserve soil moisture and prevent wind erosion, and therefore increase crop yields. (Crops immediately next to the windbreak may be adversely affected by competition, such as shade.) Border plantings are one of the best niches to exploit for the production of tree products (poles, timber, fuelwood, etc.), and windbreaks serve this duel role making them important even when winds are not a crucial problem. Windbreaks can be planted in a variety of spacings and arrangements. A single row of trees can form a reasonable windbreak for small farms with limited space, particularly when planted with a hedge. For windy areas, a three tiered windbreak is recommended (a hedge, a row of medium-sized trees, and a row of larger trees). Windbreak trees do not necessarily require extensive management. They can be allowed to grow and serve solely their windbreak function. Depending on species, they can also be pollarded to encourage lateral growth and provide needed tree products. Trees can be harvested from windbreaks but this should be planned to avoid gaps in the windbreak, especially during crop seasons. Winds can be "funnelled" through gaps leading to adverse effects on crops inside the gap, canceling positive gains from the intact windbreak. Windbreaks can be planted with a wide range of species. Tree form is important, but not critical. Trees with a dense canopy and a large surface area will reduce wind speed the best. Farmer’s needs for tree products can play into species choice, ex., if fodder is needed, then fodder trees should be used in the windbreak. Important NFT genera for a medium-sized windbreak include: Acacia (particularly Australian species), Alnus, Calliandra, Erythrina, Inga, Leucaena, Pithecellobium, Pongamia, Robinia, and Tipuana. Most appropriate NFTs for tall windbreaks come from the genera Acacia (particularly Australia), Albizia, Casuarina, Dalbergia, Mimosa, Parkia, Paraserianthes, and Pterocarpus. |
