By Justin Nyakudanga

NCT has developed a strong Eucalyptus hybrid clone programme, focusing on hybridising Eucalyptus grandis with other species, such as Eucalyptus smithii, to produce fast-growing trees that meet the requirements of international wood chip markets and are tolerant to various pests and diseases.

Wattle and E. smithii command premium prices in international wood chip markets due to their wood properties, and NCT Tree Farming prioritises these species on suitable sites.

By combining disease resistance, climate adaptability, and economic viability, E. grandis × E. smithii hybrids, such as the GS211, offer a sustainable solution for expanding commercial planting into challenging environments.

NCT's Hybrid Clone Consortium (HCC) collaborates with research partners, including the Institute of Commercial Forestry Research (ICFR), the Tree Protection Cooperative Programme (TPCP), the Sappi Technology Centre, as well as nurseries and their grower members across KwaZulu-Natal, to develop and plant hybrid progenies.

The Eucalyptus grandis x smithii hybrids have garnered attention because they combine the beneficial traits of both parent species, E. grandis and E. smithii.

The first hybrid progeny trial was established in 2007 at NCT's Baynesfield farm between Pietermaritzburg and Richmond. From this trial, 16 "plus" or good trees were selected, felled, and left to coppice or produce shoots for cuttings.  

In 2016, trials were established at NCT's Enon, Richmond, Baynesfield, Commondale, and Ingwe sites in the KZN Midlands area. The four sites differ in altitude, annual mean temperature, rainfall, and other factors, including their susceptibility to frost.

The objective was to assess the viability of the hybrids and compare them with their parent species and other clones. These comparisons are crucial in understanding the hybrids' potential for commercial application, especially in pulp and paper production, where wood properties play a significant role.

In 2023, Sappi Technology Centre was commissioned by NCT to investigate the pulp and paper-making qualities and wood densities of the E grandis x smithii clones.  

After eight years (2016–2024), the trees from the four trial sites were assessed. Four variables were evaluated: survival, tree diameter at breast height (DBH), basal area (a measure of tree growth), and wood properties.

The E. gxsm performance was compared with that of pure E. smithii, E. dunnii, and E. grandis and E. grandis x nitens 2107..

It was found that trial clones B211 and B223 had better paper-making properties than pure E. smithii. B211 also had the highest tensile, burst, and tear strength compared to B223, and E. smithii had the lowest strength properties.

Overall, the survival, diameter at breast height (DBH), basal area, and wood properties of B211 outperformed those of the rest. The B211 clones are available and sold as the GS211 hybrid in nurseries.

Is the E. grandis x smithii hybrid worth growing?

A recent webinar hosted by NCT discussed the market acceptance of GS211. Two tools were used to compare the GS211 hybrid and the pure E. smithii: the enumeration data of both species and the Nett Depot Price (rands per ton).

Enumeration of the GS211 showed that it had a mean annual increment (MAI) of 30.37(ton/ha/yr) at seven years compared to that of E. smithii with 19.90 ton/ha/yr.

The Nett Depot Price per hectare is calculated by subtracting the cost of tree harvesting, extraction, transportation, and seedling costs from the Mill Delivered price.

The average Nett Depot Price of the good, average site and marginal sites for GS211 was R166,452.42 per hectare compared to pure Smithii at R151,150.71/ha and another clone, GS270, which was R164,031.47.

Species/Clone	Plot survival	Average DBH (cm)	Average height (m)	MAI (ton/ha/yr)	Age (Years)	Nett Depot Price (R/hectare)
GS211	0.95	16.25	20.55	30.37	7	R166 452.42
E. smithii	0.73	15.64	18.62	19.90	7	R151 150.71
GxSm270	0.93	15.70		Not provided	7	R164 031.47

Points to remember about GS211

• It requires a growing altitude range of between 800m and 1,300m.
• It is not frost-tolerant.
• It is disease tolerant and can be planted in areas limited by diseases, such as Phytophthora (which attacks E. smithii), in southern Mpumalanga and northern KZN.
• It can be planted on marginal sites where pure E. smithii is established.
• E. smithii remains the preferred species among NCT customers; hence, the GS211 species should not be seen as a replacement for E. smithii.
• The GS211 will continue to be tested across a range of mean annual precipitation and temperature conditions to refine and expand its site suitability requirements.
• The GxSm270 hybrid must be bulked up first and will only be available in 2027.

The GS211 clone is available from HCC member nurseries, including TWK Sunshine Seedlings, Sutherland Seedlings, CPS Seedlings, and Ezigro Seedlings.

By Geekstreet - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=69117140