Growing Trees for Pole Markets

The annual supply of timber to the South African pole market is estimated at 600 000m³ to 700 000m³. Wooden poles compete with steel and concrete in building, fencing, electricity, transmission and fixed telephone line applications. These poles are an important product for the establishment of fixed infrastructure and provide a niche market for timber farmers. However, pole markets tend to be erratic, and growers must be flexible in terms of felling dates and supply of different commodities. The two main markets to supply are building/fencing and transmission poles.

Eucalypt varieties to plant

E. grandis is the preferred species for pole production in South Africa. This species can be grown on sites from the coast up to 1100m, however, it is prone to frost and snow damage at higher elevations. E. grandis is also susceptible to several pests and diseases and in recent years hybrid clones have been developed that are suitable for pole markets, these are generally more resilient to climatic and biotic threats:

• E. grandis x E. urophylla (GU) hybrids are suitable for subtropical and warm temperate sites and generally produce good poles, they also coppice very well, and 2 stems/stumps can be left- for small diameter poles.
• E. grandis x E. nitens (GN) hybrids are suitable for cool temperate areas and certain clone varieties can be supplied to pole markets. Growers can consult with NCT staff or the seedling supplier regarding which varieties are preferred.
• E. Vruphilia x E. saligna (GS) and E. grandis x E. longirostrata (GL) hybrids can also be grown for pole production.

Silviculture

Sites and Stocking: To achieve maximum pole recovery one must identify suitable sites to grow trees for specific markets.

Building and fencing poles should be grown on poorer sites with a Mean Annual Increment (MAI) of less than 20 tonnes. These compartments can be planted at 1666 stems per Ha (2.5 x 2.5m or 3 x 2m) and felled at 5-6 years.

Sites with MAI’s greater than 20 tonnes can be identified for growing transmission poles and planted at1666 stems per Ha. These blocks must be thinned at about 5 years to 700 stems/Ha. The thinning’s can be sold as small poles. Alternatively, plant at 3 x 3m and thin to waste at about 4 years. Thinning is done so that the stand produces large, high-quality trees which can be sold at a premium price. The number of trees per hectare affects yield and growth of trees, as do site quality and age. Thinning also helps to prevent stress which may induce pests and diseases. Clear-felling of transmissions can take place at ten years on very good sites and at 12 years on weaker sites.

Coppice management: Compartments managed for building and fencing material can be coppiced for 1 rotation before replanting. Coppice should be reduced to 2 stems per stump.

Compartments identified for production of transmission poles should be replanted after each rotation.

Identifying and managing specific compartments on a timber farm for pole production will result in better pole recovery and profitability. However, pole markets tend to be dynamic and timber growers need to be flexible in terms of felling dates and product specifications to reap the full benefit of supplying these lucrative markets.

Written by: Craig Norris, NCT’s Tree Farming Manager 

Source: NCT Forest – Pages 14 – 16

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