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2. agriculture and forestry
3. crops and seed

Eucalyptus trees
July 2012
Where do eucalyptus trees (eucalypts) come from?
They originate mainly from Australia where they grow
in environments ranging from deserts to swamps and
mountain sides.
Are eucalypts indigenous to South Africa?
No, they are not. In South Africa, eucalypts are
classified as an exotic species.
What characteristics do they have?
They are generally long-lived, evergreen species
belonging to the angiosperm family. Many, but not
all are known as ‘gum trees’ because they exude
large amounts of sap from any break in the bark.
There are over 700 (species) of eucalypts.
Classified as hardwoods, eucalypts are among
the fastest growing woody plants in the world (with
average annual growth rates up to 100m3/ha/year).
Eucalyptus is the most valuable and most widely
planted variety of plantation forest tree species in
the world (> 20 million ha) due to its wide adaptability,
extremely fast growth rate, good form and excellent
wood and fibre properties.
Eucalypt plantations worldwide have expanded
in the last 60 years because of the superior fibre
and pulping properties of eucalypt species and
the increased global demand for short-fibre pulp.
In today’s ‘new carbon economy’, eucalypts are also
receiving attention as fast-growing, short-rotation,
renewable biomass crops for energy production.1
Myburg, Z and other members of the Eucalyptus
Genome Network: Sequencing of the Eucalyptus Genome,
A Proposal to DOE-JGI, June 2006
1
Eucalypts belong to a group of plants known
as angiosperms — plants that flower and form
fruits with seeds. Seeds are enclosed in a dry or
fleshy fruit that develops from the ovary within
the flower.
Pine trees are in a group of plants called
gymnosperms — meaning ’naked seed’
because,unlike a flowering plant, the seeds of
pine trees are not inside a fruit, like an apple,
but outside attached to a pine cone.
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What are they used for?
The fibre length of eucalypts is relatively short and
uniform with low coarseness compared to other
hardwoods commonly used as pulpwood. While the
fibres are slender, they are relatively thick walled.
This gives uniform paper formation and high
opacity — important for all types of fine papers.
The low coarseness is important for high quality
coated fine papers. Eucalyptus is suitable for many
tissue papers as the short, slender fibres give a
high number of fibres per gram and low coarseness
contributes to softness. Certain eucalyptus species
are very good for kraft pulping and chemical
cellulose purposes.
In addition, eucalypts are used for a diverse array of
products including sawn timber, mine props, poles,
firewood, charcoal, essential oils, tannin and for
honey bees. In rural communities in many developing
countries, eucalypt wood is an important source of
fuel and building material.
Do they have any disadvantages?
Yes. Living eucalypts are prone to growth stresses,
evident in the warping and splitting of logs
and boards. Defects like this can reduce the general
quality of the end product and limit the usefulness
of the wood. Additional traits that can be important
in determining the value of eucalypt wood include:
basic density, mechanical properties, and juvenile
wood content, all of which can be modified through
breeding programmes.
In addition, productivity can be enhanced with
effective risk management strategies such as species
site matching, maintaining genetic diversity and
reducing stress caused by negative impacts such
as drought, frost, snow, pest and diseases.
Why is quality of wood fibre so important?
Wood quality is critically important to our industry
as 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. This is
determined by the relative proportions of cellulose,
lignin, hemicelluloses and extractives in the wood.
The physical attributes of fibres, such as fibre length,
cell wall thickness and diameter are also important
for pulp and paper qualities including brightness,
opacity, absorption, light scattering, tear, tensile and
burst strength.
PLANET
Wood quality is influenced by three major factors;
environment, genes and management factors. The
environmental factors include soil, geology, climate
and topography. The many characteristics of soils,
such as chemical composition, texture, structure, and
depth affect the growth of a tree as they affect the
supply of water and nutrients. The eucalypt species
Sappi grows have different growing preferences
and fibre quality and we manage this by carefully
matching species to sites.
In terms of genetics, our breeding programmes
ensure we select the best individuals. Seeds mostly
come from our own seed orchards where the parent
trees have been specially selected for their growth
qualities and desirable pulping characteristics.
Selected trees are also propagated vegetatively, by
rooted cuttings, to increase the spread of individuals
with good growth and pulping properties. Over 15
years, our research efforts have resulted in a 60%
improvement in eucalypt plantation yield. We are not
only interested in selecting trees that pulp well (ie
that are easy to process at the mills), we are also
interested in understanding how wood is formed in a
tree. For this we need to work at the molecular level
to determine the genes that are involved in wood
formation. The recent sequencing of the eucalypt
genome will provide invaluable information regarding
the discovery of wood-forming genes.
Tree genetics and genomics offer the means
to accelerate tree improvement. In July 2007,
the launch of an ambitious international effort to
decode the Eucalyptus genome was announced.
We were involved through our membership of
the Eucalyptus Genome Network (EUCAGEN,
www.eucagen.org) a worldwide network of
eucalypt genome researchers. The project was
managed by Professor Alexander Myburg, who
is also the leader of Sappi’s Wood and Fibre
Molecular Genetics Programme (WFMGP) at
the University of Pretoria.
The sequencing of the genome was
completed at the end of 2009 and the first
assembly (alignment of the genome) and
annotation (attaching biological information
to the sequences) of all the genes for the
E grandis genome was completed and
released in January 2011 on the phytozome
genome database, a site that facilitates
comparative genomic studies in green plants.
(http://www.phytozome.net/).
While there have been extensive genomic
studies of herbaceous plants, this is the
first comparative genomic study of woody
plants. Sequencing the E grandis genome
has not only given us an excellent reference
for gene and marker discovery, but also
enabled us to link the genome sequence to
the physical traits at the population level.
2
By determining the linkages between genetic
variation, gene expression, wood properties
and metabolite levels, we now have a much
better understanding of the genetic control of
wood formation in trees.
What types of eucalypts are grown in Sappi’s
plantation forests?
The major hardwood species grown include:
Eucalyptus dunnii, Eucalyptus grandis, Eucalyptus
nitens, Eucalyptus smithii and a range of hybrids,
as well as wattle (Acacia mearnsii). The softwoods
we grow are all pine species including Pinus patula,
Pinus elliottii, Pinus taeda and some pine hybrids.
Recently, both locally and overseas, E dunnii has
become more popular because of its naturally
good form, high wood density, adaptability to a
range of site conditions and tolerance to pests
and diseases in the temperate planting ranges.
E dunnii is classified as mildly drought tolerant,
susceptible to wind, frost and snow damage (although
it generally recovers well). It is ideally suited to sites
in the summer rainfall regions of South Africa with
average temperatures higher than 15.5°C and
average annual rainfall in the range 822–925mm
for optimum growth. It coppices well and the growth
form, small canopy and high wood density make it
especially well-suited to harvesting operations. This
species strips relatively easily and has above average
density with a range of pulping properties suitable for
both chemical cellulose and kraft pulping processes.
Currently Sappi’s breeding programme probably has
one of the most extensive collections of E dunnii
material, comprising more than 700 individual
families from 20 different regions in Australia.
This valuable resource gives Sappi breeders
the genetic flexibility to identify the most suitable
material for our end-uses in terms of growth and fibre
properties. This gene pool will also allow for some
protection against pests and diseases that could
challenge the species in the future.
The seed for these seedlings comes from a range of
orchards with varying levels of genetic improvement.
All seed is collected by hand using skilled tree
climbers, it is then processed and cleaned.
Each clean kilogram of seed produces enough
seedlings to establish between 430–450ha of land.
All seedlings leaving the nurseries are assessed
in terms of the Sappi Plant Quality Index (PQI).
Developed in-house to assess the quality of seedlings
and cuttings, the PQI ensures that they meet certain
physical and physiological specifications and that
acceptable survival and growth is achieved.
PLANET
Coppicing is a traditional method of woodland management which takes advantage of the fact that many
trees make new growth from the stump or roots if cut down. In a coppiced plantation, young tree stems are
repeatedly cut down at near ground level. In subsequent growth years, many new shoots will emerge, and,
after a number of years the coppiced tree, or stool, is ready to be harvested, and the cycle begins again.
Characteristics of eucalypt species on Sappi’s plantations – at a glance
Eucalyptus dunnii
Eucalyptus
grandis
Historically most
important hardwood
for SA forestry
industry. Good
characteristics
for kraft pulp and
chemical cellulose
Ideal growing
conditions
Optimum
average annual
temperature and
rainfall
Coppicing
and stripping
characteristics
Ideal growing
conditions
Summer rainfall
regions of South
Africa
Higher than 15.5°C
Will coppice well
Susceptible to
wind, frost and
snow damage but
generally recovers
well
Humid to sub-humid
conditions with a
low incidence of
frost
Higher than 17°C
Good, ideal for
second rotation
coppice crops
and strips easily
except in drought
conditions
Not suitable for
areas where frost
and snow occur
Does not coppice
well and the
ability to coppice
decreases with age.
This species strips
relatively easily
and has good kraft
pulping properties
Frost tolerant,
with good snow
tolerance.
Disadvantages of
this species are that
it does not flower
very well, making
the turnover of
generations difficult.
It is difficult to root
cuttings; and is
susceptible to a
number of pests
and diseases
Good, ideal for 2nd
rotation coppice
crops
Cold tolerant, but
not frost hardy
with moderate
snow tolerance.
This species strips
relatively easily
during summer and
has above average
density and good
pulp properties
Eucalyptus nitens
822–925mm
Higher than 900mm
Cooler sites in the
summer rainfall
Good characteristics regions
for kraft pulping
13–15°C
Eucalyptus smithii
5–17°C
Deep well drained
soils on cool sites
in summer rainfall
regions
810–899mm
819–936mm
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PLANET
Eucalyptus hybrids have been developed for any one of three reasons:
To combine desired traits of two species
To exploit hybrid vigour, or to
Increase the adaptability of a eucalypt species to areas which are marginal for the parent species.
Some of the more popular hybrid combinations include E grandis x E urophylla (combining good growth with
E coniothyrium tolerance), E grandis x E camaldulensis (combining good growth with drought tolerance) and
E grandis x E nitens (combining good growth and rooting ability with cold tolerance).
E grandis x E urophylla or E grandis x E camaldulensis are grown in the sub-tropical zones while E grandis x
E nitens are pre-dominant in the cooler temperate zones.
Do eucalypts use more water than pines?
Yes, they use on average 15–30% more water than pines, growing under the same conditions and at similar ages.
This does not automatically mean that converting a plantation of pine trees to eucalypts will reduce stream
flow by 15–30% because the rotation length (the point at which trees are harvested) is different and trees take
up water differently, depending on the state they are at in their life cycle. In Sappi’s plantations, eucalypts are
generally harvested at ten years while pines are harvested at 18 years.
John Davidson, consultant to the Food and Agriculture Organisation (FAO) suggests that eucalypts are more
efficient users of water than crops when total biomass produced is expressed as a function of water used.
He presented the following information taken from results of crop water usage in Australia.
Water use by plants through evapotranspiration (litres/kg of total biomass or harvested commodity produced) 2
Plant
Water use per total
biomass
(litres/kg)
Harvest index
Water use per harvested
biomass
(litres/kg)
Cotton/coffee/bananas
3,200
0.25
800
Sunflower
2,400
0.25
600
Soybean
1,430
0.35
500
Potato
1,000
0.60
600
Eucalyptus
785
0.65
510
Finger millet
592
0.40
225
What about nutrient uptake?
According to John Davidson: “When compared with a range of crops, (the) eucalypts can achieve a high
biomass production on a low nutrient uptake, as little as one-half to one-tenth that of most agricultural and estate
tree crops.” 3
Can the same pulping process be used for both hard and softwoods?
Generally speaking, a pulping and bleaching operation designed for softwood pulp can also produce hardwood
pulps without significant changes to the fibre line. The reverse does not hold: A mill designed with pulping and
bleaching facilities for eucalypt pulp cannot reliably produce softwood pulp in the same line at comparable
production rates. This relates to the different xylan content (xlyan is a complex carbohydrate found in the cell
walls of plants) between the two kinds of pulp.
2
Davidson, J Ecological Aspects of Eucalyptus Plantations (http://www.fao.org/docrep/005/ac777e/ac777e06.htm)
3
As above
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PLANET
The differences between hard – and softwood trees in Sappi’s plantations
Hardwood trees
Softwood trees
Type of tree
Mainly eucalypts
Pine
Type of fibre
Short
Long
Average length of fibres
Less than 1mm
3mm
When harvested
At approximately 10 years
At approximately 18 years
Differences in pulping
Low levels of extractives,
no soap recovery
High level of extractives, soap
‘skimmings’ converted into tall oil
and sold on
Features of end-product
Bulk, smoothness, opacity
High tensile strength, good
runnability on printing machines
Typical products
Writing papers, printing
papers, tissue papers and
chemical cellulose
Shipping containers, grocery bags,
corrugated boxes. Also suitable for
writing and printing
Hectares planted per species on Sappi’s Southern Africa sites, January 2010
Did you know?
Eucalyptus 47%
General uses for eucalyptus oil
Pine 28%
Eucalyptus is used in many medicines to
treat coughs and the common cold. It’s found
in many lozenges, cough syrups, rubs, and
vapour baths. Herbalists often recommend
using fresh leaves in teas and gargles to
soothe sore throats and treat bronchitis
and sinusitis.
GU and GC clones 4 17%
Wattle 8%
Distribution of pine species
Ointments containing eucalyptus are also
applied to the nose and chest to relieve
congestion. Eucalyptus oil helps loosen
phlegm, so many people inhale eucalyptus
steam to help treat bronchitis, coughs, and
the flu.
P patula 61%
P elliotti 29%
P taeda 7%
Plaque and gum disease
Other pine 4%
Eucalyptus oil is also rich in cineole,
an antiseptic that kills bacteria that can
cause bad breath. Eucalyptus is used
in some antiseptic mouthwashes, along
with other oils, and the mouthwashes
have been shown to help prevent plaque
and gingivitis.
Distribution of eucalyptus species
E grandis 36%
E dunnii 36%
Other uses
E amithii 15%
On the skin, eucalyptus oil has been used
to treat arthritis, boils, sores and wounds.
The oil is also used in some insect
repellents, and one study found that an oil
of lemon eucalyptus product may also keep
ticks away.
E nitens 9%
E macarthurii 2%
Other eucalypt 2%
GU and GC refers to the Eucalyptus grandis hybrid clones; E grandis x E urophylla and E grandis x E camaludulensis.
* PECH refers to the pine hybrid cuttings; Pinus elliottii x Pinus caribaea (0%).
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