Improved Pruning Techniques

Background Some tree species, whether they are planted specifically planted or grow naturally, yield some forage that may be of value to livestock. Animals can directly browse the shrubs or the low branches. The high branches or the leaves that are not accessible to animals can be cut by the herders and made available to the cattle. It is important that the exploitation of these leaves must respect some rules to keep the trees alive and preserve their longevity. If not, the livestock will contribute to reduction in numbers of trees and ultimately to deforestation. The seasonal availability of tree leaves is not the same as that of the grass or herbaceous layer. Often, trees bear green leaves when grasses are dry and not attractive to herbivores. Tree forage therefore appears to be a useful complement of grasslands in many regions. As many tree species can have a multipurpose use (wood, fruits, shade, soil protection, windbreak, marker, as well as forage), the appropriate techniques for harvesting tree leaves have to maintain the vitality of trees and the tree populations while at the same time allowing some of these other uses. | Background Techniques Targeted Livestock System Impact Application Context Monitoring: EIA Indicators References

Techniques

Foresters distinguish different techniques of branch cutting (see Figure 1). The technique adopted to harvest the forage has to be chosen and implemented according to the production objectives, the biological characteristics of the species, the agroecological zone and the season. The frequency of harvesting has to be considered. | Figure 1

Severe cutting techniques such as trimming (l’écimage), pollarding (l’étêtage), coppicing (la coupe en taillis) just leaving a stump are inadvisable. Pruning techniques (les méthodes d’élagage) are implemented with the objective of creating a firm and well balanced structural skeleton, respecting the natural growth tendency of the species. Little branch pruning (l’émondage) consists in eliminating dead or small branches and the suckers that tend to weaken the tree.

Pruning also aims to obtain the maximum amount of forage. The shape and density of trees obtained after repeated pruning and tree construction have an effect on the production of leaves (see Figure 2 below).

Figure 2 – Potential production of Morus alba leaves according to the shape and spacing of plants.

Tree Form | Number of stems per hectare, and (individual spacing) | Average Yield per hectare, and (per plant) | Maximum productive age
Standard | 204 (7 x 7 m) | 10,000 kg (50 kg per plant) | 22 years
Dwarf | 2,500 (2 x 2 m) | 20,000 kg (8 kg per plant) | 10 years
Cordon | 2,500 (2 x 2 m) | 20,000 kg (8 kg per plant) | 10 years
Shrub | 20,000 (1 x 0.5 m) | 25,000 kg (1.25 kg per plant) | 6 years

Morus alba (White Mulberry): This is a fast-growing tree with a dome-shaped crown. It is used primarily as a shade tree, but can be grown in rows to produce a screen or barrier. Leaves are the main food for silkworms.

Low pruning improves vegetative reproduction. The pruning frequency and intensity have noticeable effects on tree growth, leave production and longevity. The impact on roots plays a role on soil structure and fertility. After pruning, part of the thin roots die, reducing the capacity of nitrogen fixation of legumes, but creating tiny tubes in the soil improving soil structure and increasing air and water circulation.

Targeted Livestock System

Grazing systems (mostly natural vegetation in rangelands or planted trees in farms and ranches), mixed systems (naturally occuring or planted trees and agro-forestry).

Grazing Systems

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

Mixed Systems

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

Industrial Systems

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

Impact

- Positive environmental impact

- Decrease degradation of vegetation
- Minimise tree degradation,
- Improve tree forage productivity and lengthen productivity period,
- Improve grass cover under trees.

- Negative environmental impact

- Decrease productivity for a few tree species.
- Reduce some other functions of trees (shade, windbreak, habitat) in ecosystem.

- Livestock productivity impact (groups: milk, reproduction, meat, health, feed...)

- Improve animal feeding with good or high value forage production.

Context of Application

Positive Factors | Adapted tree management legislation and land tenure policy.
Negative Factors | Unadapted legislation enhanced by mismanagement of tree population.

Monitoring: EIA; Indicators

- Number of tree species used for forage harvesting.
- Forage tree density.
- Length of season using tree leaves as forage.
- Intensity and frequency of pruning.

References

Bellefontaine R., Gaston A., Pettrucci Y. 1997. Aménagement des forêts naturelles des zones tropicales sèches. Cahier FAO Conservation N° 32. FAO, Rome, Italy, pp. 316.

Dommergues Y., Duhoux E., Diem H.G., 1999. Les arbres fixateurs d’azote. Caractéristiques fondamentales et rôle dans l’aménagement des écosystèmes méditerranéens et tropicaux. CIRAD, Espace 34, FAO, IRD, pp. 499.

Michau E., 1990. L’élagage, la taille des arbres d’ornement. IDF, Paris.

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