Live Tree Fences and Ligneous Windbreaks

Environmental Issues Tree plantations on plot boundaries have several advantages for livestock-farming: creation of a fence limiting the movement of animals, protection against the wind and harshness of the sun, occasional forage resource. Hedges are places of plant and animal biological diversity whose role in constructing landscapes is important, but they also act as shelter for predators. | Environmental issues Objectives Techniques Costs Targeted Livestock System Impact Example References See Also

Objectives

Crop and livestock farmers plant live fences with the following aims :

> - Formal boundaries and land tenure: marking out territory,
> - Protection of crops and investment against animals straying or escaping.
> - Management of grazing land: controlling herds and their movements in order to manage grazing land.
> - Improvement of micro-climatic conditions for animals: protection against the wind and sun
> - Prevention of soil erosion.

Living hedges can act as a live fence, either alone, or backed up with strands of barbed wire (or other fencing material). They are also a tree plantation and a wind-break. Trees can serve as an occasional forage resource through simple pruning (see Pruning techniques), and a source of wood, fruit, and medicine.

Techniques

Live fences can be divided into two basic categories; living fence posts and live barriers or hedges. Live fence-posts are widely spaced, single lines of woody plants that are regularly pollarded and used instead of metal or wooden posts for supporting barbed wire, bamboo or other materials. Hedges are thicker, more densely spaced fences that generally include a number of different species and usually do not support barbed wire. The International Center for Research in Agroforestry (ICRAF) currently defines live fencing as, "a way of establishing a boundary by planting a line of trees and/or shrubs at relatively close spacing and by fixing wires to them."

The primary purpose of live fences is to control the movement of animals and people, however, they have proven to be extremely diverse, low risk systems that provide farmers with numerous benefits. Besides their main function (serving as a barrier), living fences may provide fuelwood, fodder and food, act as wind breaks and enrich the soil, depending on the species used.

Hedges are a succession of trees or bushes planted very close together in a single row, or sometimes two or three rows. The plants can come from cuttings, be sown directly on the site or come from nurseries.

Hedges should be planted where there is little risk of bush fire. They should be weeded regularly. Trimming is desirable when plants reach 70-100 cm high in order to strengthen the effectiveness of the hedge at the bottom. Afterwards trimming aims at limiting the extension of the hedge in both width and height.

Live fence posts are commonly found in conventional barbed wire fences. In many cases, the trees and shrubs that appear along fence lines, originate from seeds deposited by birds perching on dead fence posts and the fence wire. In other cases, farmers may deliberately plant stakes of easy to root species such as Gliricidia sepium, Erythrina spp., Spondias spp., and Bursera simarouba. The live fence posts are far more durable than traditional wooden posts as they are less prone to attack by termites and decay by fungi.

Costs

Creation of living hedges is an operation which essentially requires labor. The main financial cost is purchase of seeds, cuttings and especially nursery plants, as well as the labour required for preparation and planting. Under some circumstances it may be necessary to protect young trees from browsing or other damage for several years. One should estimate between 2000 and 4000 plants per km of hedge, highest density being the most effective. It is sometimes difficult to find sufficient quantities of cuttings and/or seeds necessary to make long hedges.

Targeted Livestock Systems

- Grazing system and mixed system, in conditions of farming and ranching, to organize pasture management and rotations.
- Extensive grazing system or mixed system to protect cropping areas against livestock.

Grazing System

LGA | LGS1 | LGS2 | LGS3 | LGH1 | LGH2 | LGH3 | LGT1 | LGT2 | LGT3
N | N | Y | Y | N | Y | Y | N | Y | Y

Mixed System

MCG | MCR | MCC | MFF | MEF
Y | Y | Y | Y | Y

Industrial System

IFP | IPL | IPG | IRM | IDU | ISL | ITN | IMP
N | N | N | N | N | N | N | N

Impact

- Positive environmental impacts

- Improvement of the micro-climate (wind-break effect).
- Reduction of water and wind erosion.
- Improvement of rain water infiltration.
- Increased biodiversity of plants (many spontaneous species in the hedge).
- Increased biodiversity of animals (habitat for different species).
- Improved graze management and rotation.
- Forms part of the diversity of the landscape.
- Certain types of hedge may include economically productive species, e.g. sisal, citrus

- Negative environmental impacts

- Concentration of bird predators.
- Presence of snakes and other harmful animals.

- Impacts on livestock productivity

- Optimization of graze management hence improved meat production.
- Improvement of grazing animals' comfort, with a positive impact on their health and growth.
- Reduced risk of conflicts between livestock farmers and crop farmers, but slightly reduced areas under grass or crops.

Context of Application

Intensification of livestock and intensification of crops (market gardening, orchards, out-of-season crops)

- Favorable conditions:

- security of land tenure
- sufficient space for crops
- availability of plants

- Unfavorable conditions

- Risk of fire
- Land tenure regulations in communal areas
- Existence of risks or depressive effects on neighboring crops
- Unavailability of funds to establish the hedges.

Example: The most promising species in West Africa are listed in Table 1

Table 1 - Recommended species for live fences in dry and semi-arid areas of West Africa (from Louppe, 1999).

Species | Rainfall 400 - 700 mm | Rainfall 700 - 1000 mm | Rainfall 1000 - 1300 mm
Acacia mellifera | X | X |
Acacia nilotica | X | X |
Acacia senegal | X | X |
Agave sisalana |  | X | X
Bauhinia rufescens | X | X | X
Citrus lemon |  | X | X
Commiphora africana | X | X |
Dichrostachys cinerea |  |  | X
Euphorbia balsamifera | X | X |
Haematoxylon brasiletto |  |  | X
Jatropha curcas | X | X |
Moringa oleifera |  | X | X
Prosopis juliflora | X | X |
Ziziphus mauritiana | X | X | X
Ziziphus mucronata |  |  | X

References

Louppe, D., Yossi H. 1999. Les haies vives défensives en zones sèches et subhumides d'Afrique de l'Ouest. Atelier Jachères, Dakar.

Ariga, E, S. 1997. Availability and Role of Multipurpose Trees and Shrubs in Sustainable Agriculture in Kenya. Journal of Sustainable Agriculture. 10:2/3, 25-35.

> Abstract: More than 60 trees and shrubs species with multipurpose usage were collected from southeastern and southwestern parts of Kenya. Biased sampling on pre-determined target species was carried out. Seeds and herbarium samples were collected. The plant species and their alternative uses are listed. The information on plant usage was obtained from the local community and other established sources. The plants or their parts are used for food, fodder, medicine, soil conservation, and fertility improvement, shade, wind barriers, live fences, fuel, timber, fibre, wildlife habitat and extraction of some industrial products. While different plant parts of the same species are useful, others are poisonous.

See Also

Cherry, S.D. & Fernandes, E.C.M. 1999. Live Fences. http://ppathw3.cals.cornell.edu/mba_project/livefence.html (includes good example photos and descriptions as well as additional references).

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