Associated Forest Cover
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In Australia, saligna eucalyptus is usually found in mixture with
tallowwood eucalyptus (Eucalyptus microcorys) and
blackbutt eucalyptus (E. pilularis), the main coastal
species of New South Wales, and is also found associated with
several other eucalypts. It seldom grows in pure stands, whereas
the closely related rosegum eucalyptus is typically found in pure
stands (13). The common names used follow those of Bryan and
Walker (2).
In Hawaii, saligna eucalyptus has been planted in mixture with
three species of eucalyptus-tallowwood, robusta (Eucalyptus
robusta), and rosegum-with melaleuca (Melaleuca
quinquenervia), Formosa koa (Acacia confusa), horsetail
casuarina (Casuarina equisetifolia), silk-oak (Grevillea
robusta), and a host of other species. On most sites, it has
outgrown and shaded out or badly suppressed all of these species
except the equally fast growing rosegum eucalyptus and the
tolerant Formosa koa. In closed stands, about the only understory
species found are strawberry guava (Psidium cattleianum) and
occasional treefern (Cibotium spp.).
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Climate
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In Australia, the tree grows from sea level to 300 In (1,000 ft)
in the South and to 1220 m (4,000 ft) in the North. The climate
within this range is warm-temperate to subtropical, with winter
frosts to -15° C (5° F) at the higher elevations (12).
In New Zealand, seedlings were frost tolerant to a minimum
temperature of -7° C (21° F) (21). Rainfall is evenly
distributed, or has a summer maximum, and ranges from 890 to 1270
mm (35 to 50 in) annually (13).
In Hawaii, saligna eucalyptus grows well between elevations of
about 150 m (500 ft) and 1100 m (3,600 ft) where the temperature
is never below 4° C (40° F). One stand is at 1980 m
(6,500 ft) where light winter frosts occasionally occur, and the
average daytime temperature is about 16° C (60° F).
Most of the saligna eucalyptus stands have been planted between
300 and 610 m (1,000 and 2,000 ft) elevation in locations with
evenly distributed or winter maximum rainfall of 1520 to 7620 mm
(60 to 300 in) annually. The tree achieves its best growth on
sites with about 2540 mm (100 in) annual rainfall, rather than on
wetter sites, possibly because sunlight is greatly reduced by the
cloud cover on wetter sites.
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Damaging Agents
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Saligna eucalyptus grown in plantations
in many parts of the world is susceptible to the eucalyptus
canker disease, Cryphonectria cubensis. The disease kills
young trees, deforms stems, and causes basal cankers that reduce
the coppicing ability of stumps (19). Rosegum eucalyptus is
somewhat resistant and Eucalyptus urophylla, perhaps, is
immune to the disease, so these species are now being used in
place of E. saligna in many Brazilian plantings. In
Hawaii, the disease is present only on the island of Kauai. It
attacks E. grandis in Florida but is not causing serious
damage (18).
In Western Australia, two other canker diseases, Botryosphaeria
ribis and Endothia havaensis, were determined to be
pathogenic on E. saligna planted there, while another,
Cytospora eucalypticola, was present but less damaging
(14).
Phoracantha semipunctata, a wood-boring insect, degrades
wood and reduces growth of eucalyptus in many places, including
Hawaii, but is only a serious problem in trees that are stressed
by severe drought. In Australia, saligna eucalyptus is subject to
damage by Spondyliaspis psyllids, which predispose the
trees to attack by the wood-boring beetle Xyleborus truncatus
(22).
In Hawaii, wind damage is a severe problem. In January 1980, a
severe windstorm caused severe blowdown in 75 percent of the
saligna eucalyptus stands planted during the 1960's (17).
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Flowering and Fruiting
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Saligna eucalyptus trees begin to
flower at 3 to 4 years of age. Flowering in Hawaii is most
prolific during January to March but occurs to some extent year
round. In Australia, the tree also flowers from January to March;
in California, from April to June. Flowers that consist of
numerous stamen filaments surrounding a single shorter pistil
occur in umbels of 4 to 9 flowers. Before opening, the flower
buds are about 10 mm (0.4 in) long and 5 min (0.2 in) in diameter
with a short stalk (pedicel), and a blunt, rather pointed cap
(operculum) enclosing the stamens. Flowers are perfect. The
opened flowers are yellowish white and are insect pollinated.
Pollen is generally shed before the style becomes receptive, so
selfing is rare.
The fruit is a dark-brown, bell-shaped capsule 0.8 em (0.3 in)
long and 0.5 cm (0.2 in) in diameter. It is short stalked and has
four pointed, rim level, or slightly exserted valves. The capsule
ripens about 6 months after flowering but opens to release seed 1
or 2 months after ripening (12,13,20).
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Genetics
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Population Differences
In an attempt to solve the problem of confused and probably mixed
introductions of Eucalyptus saligna and E. grandis,
differences between them have been noted for mature trees in
South Africa (12), as follows:
E. saligna
E. grandis
Bark: smooth
type bluish; rough type on lower stem
Bark: smooth type white; rough type often
extends up stem
Flowering (South Africa): January to April
Flowering (South Africa); July to December
Valves of fruit: 3 or 4 pointed, straight
or spreading
Valves of fruit: 4 to 6 blunt, incurved
Root crown: Lignotuberous
Root crown: Not lignotuberous
Branches: Persistent under shade
Not persistent under shade
These characteristics vary among provenances of each species. The
northernmost provenances of saligna eucalyptus, for example, do
not have lignotubers (12). When grown in some locations, for
example, Hawaii, flowering seasons overlap and trees probably
hybridize extensively. Among 6-year-old trees of provenances
collected in Australia growing side-by-side at two locations in
Hawaii, no consistent differences were observed between E.
saligna and E. grandis in leaves, bark, or branching
habit (26).
Saligna eucalyptus produces denser wood than E. grandis, but
in Hawaii (26), and also in the Republic of South Africa (9)
where yields of the two species growing on the same sites have
been compared, the best performing E. grandis provenances
for a particular site produce a higher total weight yield than
E. saligna, despite the wood density difference.
Hybrids
Because of the wide international interest and the problems of
hybridization and identification of the two species, a comparison
of E. saligna and E. grandis populations
representative of the entire range of each species was made in
Australia (4). Distinct differences were found in seedling and
mature-tree morphology and allozyme frequencies between core
populations of the two, but intermediate types were found in some
remote locations. Core mature saligna eucalyptus had smaller
seed, upright valves (4 per fruit), and non-glaucous fruit and
branchlets as compared with E. grandis, which had larger
seed, incurved valves in 5's, glaucous fruit and branchlets.
Saligna eucalyptus seedlings had lignotubers and were glaucous;
not so, E. grandis. Saligna eucalyptus seedlings also had
smaller cotyledons and narrower, longer leaves. The allozyme
patterns found for native populations in Australia showed species
differences and were later compared to patterns found for
populations collected in the Republic of South Africa, which were
thought to be hybridized (5). All the South African trees sampled
fell within the allozyme patterns found in Australia for E.
grandis, even though several were morphologically suspect.
In addition to the Eucalyptus grandis/E. saligna complex,
E. saligna crosses with E. robusta, bangalay
eucalyptus (E. botryoides), and probably with forest
redgum eucalyptus (E. tereticornis) (12,28). In the
southern part of its natural range, a region of introgression of
E. saligna with E. botryoides exists (23).
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Growth and Yield
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Saligna eucalyptus is a fast growing
tree, well suited for producing high yields of wood fiber on
short rotations. Measurements of a plantation spacing study on a
good site at Kaumahina, Maui (29) provide an example. Four
spacings were tested: 2.4 by 2.4 m, 3.0 by 3.0 in, 3.7 by 3.7 m,
and 4.3 by 4.3 m (8, 10, 12, and 14 ft). At 2 years, trees
averaged 9.6 cm (3.8 in) in d.b.h. and 10.7 rn (35 ft) in height.
At 5 years, they had grown to 20.8 cm (8.2 in) in d.b.h. and 22.9
in (75 ft). Mean annual volume increment had already peaked at
the two closer spacings in the study and was rapidly leveling out
at the wider spacings. At 15 years, the trees in this study
averaged 26.7 cm (10.5 in) in d.b.h. and 39 in (129 ft) tall. The
largest tree was 61 cm (24 in) in d.b.h. and 49 rn (161 ft) tall.
At 5 years, the trees at 2.4 by 2.4 m (8 by 8 ft) had produced
294 m³/ha (4,200 ft³/acre), or 58.8 m³/ha (840 ft³/acre)
per year. At 15 years, these trees yielded 683 m³/ha (9,759
ft³/acre), or 45.6 m³/ha (651 ft³/acre) per year.
Trees at 4.3 by 4.3 m (14 by 14 ft) yielded 33.1 m³/ha (473
ft³/acre) per year.
These figures are comparable to those of Eucalyptus grandis/E.
saligna grown in other countries. In Kenya, a mean annual
increment over 5-year periods of 21 m³/ha (300 ft³/acre)
for the seedling crop followed by 32 m³/ha (457 ft³/acre)
for the first coppice crop was obtained (11). Other mean annual
increment figures cited for E. grandis are 14 to 45 m³/ha
(200 to 643 ft³/acre) in Uganda, 28 m³/ha (400 ft³/acre)
in Zambia, 50 m³/ha (715 ft³/acre) at 14 years in
Argentina, and 22 m³/ha (314 ft³/acre) in New South
Wales, the native habitat of both species (12).
In two 4-year-old stands in Hawaii, annual increment averaged 13
and 36 m³/ha (185 and 515 ft³/acre). The faster growing
stand yielded wood with a specific gravity of 0.41 for an
estimated annual dry-weight yield of stem wood of 15 tonnes/ha
(6.7 tons/acre).
The tallest tree in Hawaii, thought to be the tallest hardwood in
the United States, is a saligna eucalyptus. When last measured in
1979, the tree was about 50 years old, 137 cm. (54 in) in d.b.h.
and 82.3 m (270 ft) tall.
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Reaction to Competition
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Because the tree is such a fast
starter, planted seedlings can frequently grow faster than
surrounding grass and herbaceous vegetation and shade it out.
This is particularly true if the seedlings have an intact root
system when planted, as in modern tube container planting, so
that little or no "shock" occurs to delay new growth
after planting. At the upper elevational boundaries of sugarcane
fields, saligna eucalyptus grown from seed in the soil at the
time of cane harvest actually outgrew the sugarcane ratoon crop.
In Hawaii, original plantings are made on completely cleared land.
Pre-emergent herbicides, though effective, have rarely been used.
If pre-emergents are not used, one cleaning around trees that
require it is made after 3 months and, depending on the site, a
second cleaning may sometimes be made at 6 months. Further
weeding is seldom necessary. Coppice growth of saligna eucalyptus
is so rapid that competing plants are rarely a problem after
cutting.
Tests in Hawaii show that the leguminous tree Albizia
falcataria outgrows saligna eucalyptus on some sites when
planted row on row with both species equally fertilized. It is
one of the few woody plants known that can grow this fast on
sites that are suited for saligna eucalyptus. The trials of
mixing the legume with E. saligna produced increased yields of
the eucalypt on some wet sites, but reduced yields on other,
drier sites (10).
In South Africa, thinning schedules have been developed for trees
planted at 1330/ha (538/acre) that call for thinning 25 percent
of the stems present at 6 years when the stems removed are 13 cm
(5 in) in diameter, and 25 percent again at 10 years when they
are 20 cm (8 in) (12). These thinnings are continued at 3- to
5-year intervals until a sawtimber harvest is made at age 30. In
the interim, all stumps are allowed to coppice to keep the site
free of competition and to supply fuelwood crops.
Saligna eucalyptus is classed as very intolerant of shade and the
slower growing trees in a stand quickly become suppressed. In
Hawaii, crown closure is usually complete and crown
differentiation begins in 3 years in stands planted at 3 by 3 in
(10 by 10 ft). In coppice stands where numerous stems grow from
every stump, crown differentiation begins as soon as sprouts
appear. Many studies have shown that the maximum yield of wood is
obtained by not thinning coppice at all (12). However, if larger
diameter and straighter stems are desired, thinning to one to
three stems per stump is desirable.
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Rooting Habit
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Saligna eucalyptus develops roots
throughout the soil profile so that it is quite windfirm on deep
soils, but easily windthrown on shallow soils. It does not
produce a taproot. Roots are primarily from the stem below the
lignotuber, although layering sometimes occurs a short distance
from the lignotuber on buried stems. In plantations in Hawaii
that are not subject to periodic short drought, about two-thirds
of the root system is confined to the upper 61 cm (24 in) of soil
where most of the available nutrients are found. In plantations
subject to occasional drying of the surface soil, the shallow
roots are killed and a deeper root system develops.
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Seed Production and Dissemination
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Seeds are black,
irregularly shaped, and about 1.3 min (0.05 in) in diameter. They
are released along with a large amount of reddish-brown chaff
when the capsule valves open. There are 460 viable seeds per gram
(13,000/oz) of seed plus chaff (20).
Seeds are naturally dispersed by wind. They can be collected from
ripe capsules dried to open after picking. Some unopened ripe
capsules are always present on trees in Hawaii but are most
common in August and September. Fresh seeds germinate readily in
10 to 20 days without pregermination treatment. Seeds can be
stored in airtight containers for several years at 0° to 5°
C (32° to 41° F) (20).
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Seedling Development
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The seedling has obcordate (inverse
heart-shaped) cotyledons that are home epigeously as in all
eucalypts. Juvenile leaves are opposite for 3 or 4 pairs, then
become alternate, short stalked and lanceolate, and 2.5 by 5.0 cm
(1 by 2 in) in size. The adult leaves are alternate, stalked and
lanceolate, tapering to a long point, 2.3 by 15 cm (1 by 6 in) in
size (13).
In Hawaii, nursery-grown seedlings in containers reach plantable
size in 4 to 5 months. Although seedlings are hardy and will
survive bare or open-rooted planting, planting of container-grown
stock provides more assurance of success if the weather is dry
just after planting. Under adverse conditions newly planted
seedlings often desiccate and suffer leaf-drop, but such plants
usually sprout from the lower stem and recover. When this dieback
slows growth, additional weeding or maintenance usually is
required to clear competition (32).
Around the world, seeds usually are germinated in flats containing
light-textured medium, and seedlings are transplanted into other
containers after 6 to 8 weeks when a third pair of leaves begins
to appear (12). Seeds also are sown directly into beds or tubes,
but thinning of seedlings is usually required with this method
because the small seeds are difficult to handle individually.
Thinning requirements can be overcome by using pelletized seed
and seeding devices (15,31).
In Hawaii, saligna eucalyptus seedlings have been grown
extensively in open beds. Because of their rapid growth, these
seedlings usually are root pruned at 15-cm (6-in) depth at 6
months and top pruned at 8 months to a 30-cm (12-in) height. Bare
root stock frequently has not survived well after field planting,
and Hawaii's practice has now changed to growing seedlings only
in polyethylene tubes (30).
On favorable sites in Hawaii, planted seedlings grow to about 3 m
(10 ft) in height in 1 year, and 3 to 5 in (10 to 16 ft) per year
for the next 10 years. After clear cutting of a 44-year-old
saligna eucalyptus plantation, natural seedlings that became
established grew to saplings that averaged 9 cm (3.5 in) in
d.b.h., and 11 rn (36 ft) in height, 22 months after logging.
Several of these saplings were 18 m (59 ft) tall.
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Soils and Topography
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In the northern part of its range in Australia, saligna eucalyptus
extends to the slopes and ridges. In northern New South Wales and
Queensland, it is usually on the slopes, while the closely
related rosegum eucalyptus (Eucalyptus grandis) is usually
near or at the valley bottoms. Saligna eucalyptus does best on
clay loams derived from shales and requires good drainage (13).
In Hawaii, saligna eucalyptus has been planted extensively on
Histosols and Inceptisols on the island of Hawaii, and also on
the Oxisols and Ultisols of Maui, Molokai, Oahu, and Kauai. These
soils have in common moderate to strong acidity, low to very low
available nitrogen and phosphorus, and rapid to very rapid
drainage. All are formed on basaltic parent material, either
volcanic ash or rock. In other respects they differ considerably,
but all are unsuited or only marginally suited for agriculture.
Slopes are usually 10 to 20 percent.
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Special Uses
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In Hawaii, saligna eucalyptus has been used to some extent for
sawtimber, but only with considerable difficulty and expense.
Most of the milling and lumber quality problems are those
associated with growth stress-severe end-splitting of logs,
spring of cants during sawing, compression failures, and
brashness of the wood near the pith (25). Because of this, the
tree is now planted primarily for early harvest as pulpwood, or,
if it proves economic in the near future, as industrial fuelwood
to replace oil.
Elsewhere in the world, particularly in South Africa and Brazil,
the trees and their close relative, E. grandis, are grown
extensively for pulp, poles, and fuel.
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Vegetative Reproduction
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Saligna eucalyptus can sprout
prolifically from dormant buds located in the cambium throughout
the stem. After a tree is cut, shoots sprout from many points on
the remaining bark surface. Those highest on the stump suppress
those lower down and, if not broken off by wind or by weak
attachment, become coppice stems that overgrow the stump (12).
Sprouts will also grow from the lignotuber, a mass of bud tissue
at or just below the groundline. Lignotubers are found on saligna
eucalyptus from all but its northernmost provenances, but not on
rosegum eucalyptus (12). In managing saligna eucalyptus for
coppice, it is desirable to cut stumps 12 cm (5 in) or less in
height, so that the sprouts will develop from near the
lignotuber. Such sprouts generally are more firmly attached but
are frequently suppressed by sprouts arising from higher on the
stump. Lignotubers persist when stems are killed by shading,
thinning, or fire and often sprout vigorously after a mature
stand is cut (8).
Rooting of cuttings of saligna eucalyptus had been difficult (16)
until a method was developed at the Aracruz Co. in Brazil (7).
The method consists of collecting coppice sprouts that are just
beginning to harden and keeping them constantly moist while
2-leaf-pair cuttings are prepared and end-dipped in rooting
hormone. The cuttings are placed under intermittent mist in
individual containers. In Hawaii, saligna eucalyptus has been
easier to root than E. grandis, although most success
elsewhere has been with E. grandis (3,7). However, just
as was found for E. grandis in Brazil (6), cutting
rootability is variable among coppice from individual saligna
eucalyptus trees.
Tissue culture propagation has also been successful in Hawaii. The
techniques used with saligna eucalyptus are essentially those
reported by Boulay (1) for other eucalyptus species. Terminal and
lateral shoot tips of greenhouse-grown rooted cuttings are
multiplied, separated, and rooted in sterile culture, and
afterwards grown to normal size in a mist
chamber. A number of propagules of saligna eucalyptus produced by
tissue culture are now being compared in clonal progeny tests.
Grafting success has been reported for saligna eucalyptus (24,27).
Cleft, side, splice, and bottle grafting were all used
successfully, but the tests were not observed for a long enough
period to determine the extent of long-term incompatibility, a
problem with many species of Eucalyptus.
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Distribution
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Saligna eucalyptus is native to the east coast of Australia from
Bateman's Bay (lat. 36° S.) in southern New South Wales to
the southeastern corner of Queensland (lat. 27° S.) (13). In
the United States, it has been introduced into Florida,
California, and Hawaii. In Hawaii it reproduces at the edges of
planted stands. Although it was introduced into Hawaii in the
late 1800's, the tree was not planted extensively until the
1960's, when it became the principal tree used for
forestation.
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Brief Summary
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Myrtaceae -- Myrtle family
Roger G. Skolmen
Saligna eucalyptus (Eucalyptus saligna), also called
Sydney bluegum, is a fast growing tree, valuable in plantation
forestry. It grows in several warm temperate to subtropical
countries, such as Brazil and the Republic of South Africa, and
the state of Hawaii.
The name Eucalyptus saligna was given to type specimens in
1797. Another very similar but distinct species, found within the
same geographic range, Eucalyptus grandis, was not named
until 1918 (12). Before 1918, many introductions were made
worldwide of seed collected from "E. saligna" that
bore the characteristics of the type later to be called E.
grandis. In most countries where introductions were made,
therefore, considerable mixed planting and hybridization of the
two species are present. Thus, in Hawaii, most saligna eucalyptus
stands contain trees with a range of characteristics intermediate
between those of E. saligna and E. grandis.
Eucalyptus grandis is now preferred in South Africa because
it self-prunes more readily and has smaller branches (28); and in
Brazil because it is resistant to a canker disease and can be
propagated vegetatively (6). Eucalyptus saligna has grown
well where the climate is cooler; for example, in northern New
Zealand (12) and in the uplands of Hawaii. Recent provenance
tests of the two species in Hawaii suggest that E. grandis
would be a better choice than E. saligna for most
sites (26).
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