Eucalypts are a group of trees belonging to the Myrtaceae (myrtle) family, containing the genera Angophora, Corymbia and Eucalyptus. Eucalypts are generally long-lived, evergreen angiosperm plants that flower and form fruits with seeds. However, the flowers have no petals. Instead, the bloom consists of hundreds of stamens. The seeds are enclosed in a dry or woody fruit that develops from the ovary within the flower. Many eucalypts, but not all, are known as ’gum trees’ because they exude copious amounts of sap from any break in the bark.
Hybrids are the result of crossing two different taxa through sexual reproduction. Sappi produces several inter-specific (between species) hybrids, including Eucalyptus grandis x Eucalyptus nitens (often referred to as ‘GN’) and Eucalyptus grandis x E. urophylla (GU).
The eucalypts originate predominantly from Australia, where they grow in a wide variety of climatic regions, ranging from deserts to swamps to mountainsides – hence their environmental plasticity. Four species of Eucalyptus (E. deglupta, E. orophila, E. urophylla and E. wetarensis) originate outside Australia in Indonesia, the Southern Philippines and New Guinea. Eucalypts are thus not indigenous to South Africa and are classified as exotic species.
There are over 700 species of Eucalyptus that exhibit remarkable diversity across their native range. Developmental characters such as bark, leaf and inflorescence type, ability to make epicormic shoots, adaptation to fire damage, as well as tremendous chemical variation underlying herbivore defence, vary within, and between, groups. The Eucalyptus genus includes species with very fast growth rates (mean annual growth rates of up to 20-35 m3/ha/year), allowing many varieties to reach maturity as early as ten years in comparison to other hardwood species that can take 18-25 years to reach early maturity.
Living Eucalypts are prone to biotic and abiotic stresses. This includes susceptibility to numerous pests and diseases, evidenced by the presence of stem cankers, root rot, foliar wilting and necrosis that can impact survival and growth. Abiotic stresses caused by environmental factors can also result in growth stresses, which affect yield. Productivity can be enhanced with effective risk management strategies, such as genotype-by-site matching, maintaining genetic diversity, breeding for resistance, and reducing stress caused by negative impacts such as drought, frost, snow, pest and diseases.
The diversity within the eucalypts has been the basis of a multitude of uses, including timber, pulp, lignocellulosic biomass, oils, and ecosystem services. Some of their key uses include:
Wood quality is critically important to our industry. During pulp and paper manufacturing, many aspects such as pulp yield, consumption of cooking liquor and potential for bleaching, are dependent on the chemical composition of wood.
Wood quality is influenced by three major factors: environment, genetics and silvicultural management.
The major species and taxa we grow are Eucalyptus dunnii (26.6%) and two E. grandis hybrid taxa: E. grandis x E. nitens (13.0%) and E. grandis x E. urophylla (11.8%). Most of our hardwoods are eucalypt taxa; this includes a very small proportion of Corymbia henryi (<0.1%; synonym Eucalyptus henryi). We also grow a small proportion of wattle, Acacia mearnsii (0.5%). Other minor eucalypt species planted, covering 11.6% of landholdings, are E. benthamii, E. macarthurii, E. nitens, E. smithii and E. grandis. About 36.6% of our landholdings are deployed to various pine taxa.
Our current species deployment represents a substantial shift from the predominant pure species deployment of the past (e.g., E. grandis and E. nitens). The increased deployment of hybrids has been in response to major pest and disease threats.
Eucalyptus dunnii has a range of pulping properties suitable for both dissolving pulp (DP) and kraft pulping processes. A small canopy and the ease with which bark can be stripped make E. dunnii especially well-suited to harvesting. Suited to summer rainfall regions in temperate planting ranges, E. dunnii is mildly drought tolerant but susceptible to wind, frost and snow damage, from which it generally recovers well. This species is prone to the snout beetle (Gonipterus) and Eucalyptus gall wasp (Leptocybe invasa).
Eucalyptus grandis x E. urophylla hybrids
This hybrid cross combines the good growth traits of E.grandis with the Eucalyptus stem canker tolerance (Teratosphaeria zuluensis, previously Coniothyrium zuluense) of E. urophylla. It is appropriate for sub-tropical zones; humid to sub-humid conditions, but is not suited to areas where frost and snow occur.
Eucalyptus grandis x E. nitens hybrids
Eucalyptus grandis x E. nitens combines good growth and rooting ability derived from E. grandis with the cold tolerance of E. nitens, resulting in moderate frost and snow tolerance and moderate coppicing ability. Unlike E. nitens, the hybrid shows higher resistance to cossid moth and to Phytophthora root rot. It is suited predominantly to the warm and cool temperate zones.
Seeds are derived, predominantly, from our own seed orchards where the parent trees have been specially selected for their growth qualities, disease resistance and desirable pulping characteristics. For the production of hybrids, we develop control pollinated seed, by crossing selected parents to generate offspring that carry desirable traits for further testing.
All our seed is collected by hand using skilled tree climbers. It is then processed and cleaned. Our eucalypt seedlings are produced in two nurseries, one based in Mpumalanga and one in KwaZulu-Natal.
Selected trees are also propagated vegetatively, using rooted cuttings to rapidly increase the deployment of high-value individuals / varieties with good growth and pulping properties. All eucalypt cuttings are produced in large, modern nurseries. One nursery is based near Pietermaritzburg in KwaZulu-Natal and the other in Mpumalanga, where skilled staff manage selected mother plants, in large sand beds, for clonal cutting production. Recently, cutting production expanded to the use of biodegradable paper pots, which result in improved planting efficiency, growth and survival, especially on harsh sites.
All seedlings and cuttings leaving our nurseries are assessed using our in-house developed Plant Quality Index (PQI) to ensure the dispatch of top quality plants. The PQI guarantees that all plants dispatched from the nurseries meet defined physical and physiological specifications and that acceptable survival and growth is achieved.