Associated Forest Cover
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When casuarina is present through natural seeding in Florida, it
tends to form pure stands that are often nearly devoid of other
vegetation (4). It may coexist with vegetation such as Florida
fishpoisontree (Piscidia piscipula), button-mangrove (Conocarpus
erectus), myrsine (Rapanea punctata), stopper (Eugenia
spp.), randia (Randia spp.), cocoplum (Chrysobalanus
icaco), southern bayberry (Myrica cerifera), redbay
(Persea borbonia), and Florida poisontree (Metopium
toxiferum) (3).
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Climate
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In Australia, these species grow in the tropical and subtropical
north and east: C. cunninghamiana along rivers, C.
glauca in swamps, and C. equisetifolia along the
coast.
In Florida, C. cunninghamiana and C. glauca have a
wide tolerance for moisture regimes, as they are present on sites
ranging from dry to very wet but not permanently flooded. Casuarina
equisetifolia performs well on dry sites only; C.
glauca appears to be the most frost hardy, although it
will not withstand long periods below freezing, and C.
cunninghamiana is intermediate in frost tolerance. There
seem to be no climatic barriers to sexual reproduction.
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Damaging Agents
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Casuarina appears to have relatively few
insect problems. The twig girdler (Oncideres cingulata) is
harmful only to small trees; damage by the leaf notcher
weevil (Artipus floridanus) usually is inconsequential;
and one species of spittlebug (Clastoptera undulata) appears
to infest individual trees but causes no serious damage (2). The
Australian pine borer (Chrysobothris tranquebarica) has
on occasion devastated trees 5 years or less in age by girdling
the stems (17).
The major biological cause of death of casuarina on well-drained,
acid, sandy soils is a mushroom root rot (Clitocybe
tabescens) (15); Casuarina cunninghamiana may be less
susceptible than the other species. The incidence of root rot is
reduced on wetter sites, with no evidence of the disease in
alkaline soils.
Primary nonbiological losses are from lightning and frost. Killing
lightning strikes are common to casuarina that are dominant in
the south Florida landscape. Freezing temperatures can damage
well-established trees; temperatures of approximately -8° C
(18° F) kill trees less than 0.5 m (1.6 ft) in height.
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Flowering and Fruiting
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Casuarina species have been
reported to be monoecious (13) and dioecious (6); C. glauca
in Florida has not been observed to bear female flowers.
Flowering occurs principally from April to June, with numerous
minute narrow and terminal male flowers crowded in rings among
grayish scales, and rounded and lateral female flowers occurring
in light-brown clusters (9,13). Female flowers are wind
pollinated. The multiple fruit, gray brown and 8 to 15 mm (0.3 to
0.6 in) in diameter, ripen from September through December. Seed
bearing usually begins by age 5, and good seed crops occur
annually (13).
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Genetics
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The geographic seed origins of casuarina in Florida are not known.
Although trees characteristic of each species can be readily
located, classification of individual trees is sometimes
difficult because a high degree of hybridization is presumed. The
three species are found together in much of south Florida and
have compatible flowering times. A C. cunninghamiana x C.
glauca hybrid has grown faster than any of the three species
(1). Studies of individual tree collections of C.
cunninghamiana and C. equisetifolia from four areas
in south Florida do not indicate differences among trees,
sources, or species for survival through 6 months (16).
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Growth and Yield
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Early growth is rapid, and height
increments exceeding 1.5 m (5 ft) per year are common. Mature
trees in stands of C. cunninghamiana and C.
equisetifolia may reach 32 m (105 ft) in height and 41 cm (16
in) in d.b.h.; more commonly, heights of 25 m (82 ft) and
diameters of 25 cm (10 in) are attained. Initial survival rates
for planted trees are acceptable, averaging over 87 percent. One
35-year-old stand of C. glauca had a basal area of 90 m²/ha
(392 ft²/acre) composed of trees averaging 19 m (62 ft) in
height and 14 cm (5.5 in) in d.b.h.
Total aboveground dry biomass yields of young natural stands of
C. equisetifolia have been as high as 16.6 t/ha (7.4
tons/acre) per year. Such stands, with densities up to 11,400
trees per hectare (4,600/acre), have trees ranging from 0.6 to 18
cm. (0.25 to 7 in) in d.b.h., with an average of 4.3 cm (1.7 in)
at an estimated age of 7.5 years.
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Reaction to Competition
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Casuarina species are intolerant
of shade but capable of rapidly invading new sites and forming
pure stands. When young, trees are easily suppressed by some
forms of competing vegetation, especially grasses and sedges,
particularly if seedlings are not nodulated and cannot fix
atmospheric nitrogen. On a well-prepared palmetto prairie in
Florida, for example, newly planted casuarina seedlings failed to
survive competition from wiregrass (Aristida stricta) that
rapidly reinvaded the site. In the Philippines and in the
Highlands of Papua, New Guinea, however, casuarina seedlings have
been reported to compete aggressively against Imperata grass,
a weed that makes large areas of the tropics useless for
agriculture (12). Once casuarina trees dominate a site, however,
their heavy root mat and the deep litter layer tend to reduce,
even eliminate, competitors.
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Rooting Habit
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Casuarina has a spreading, fibrous root
system that can penetrate quite deeply into the soil if
subsurface moisture is available. A very dense mat of
adventitious roots may be formed in response to wet conditions.
The root hairs become infected by Frankia spp. and form
nitrogen-fixing nodules (18).
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Seed Production and Dissemination
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The conelike fruits
mature throughout the year, although heavier crops occur in the
fall and winter. When the fruits dry from December to March, the
samaras, which range in length from 3 to 8 mm (0.1 to 0.3 in),
depending on species (14), are released and wind disseminated.
Germination of the seeds is epigeal and good on moist, bare soil.
Seeds may be extracted readily from air-dried fruits. Cleaned seed
yields range from 661,000 to 1,653,000/kg (300,000 to 750,000/lb)
depending on species and location (13). Germination of seeds
stored for 2 years under conditions ranging from 6 to 16 percent
moisture content and -7° to 3° C (20° to 38°
F) can be from 40 to 50 percent (7). No pregermination treatment
is required (13). Broadcast sowing of seeds, followed by a thin
topping of soil or other nursery medium sufficient to give 215 to
323 seedlings/m² (20 to 30/ft²), can result in
outplantable seedlings within 3 months.
Seedling development is partly dependent on the presence of a
symbiont, the filamentous actinomycete Frankia spp.,
which allows casuarina to fix atmospheric nitrogen. Inoculation
of nursery-grown seedlings is therefore advisable. This can be
accomplished by application of a 10 percent suspension of ground
casuarina root nodules with water to the nursery medium (11,18).
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Seedling Development
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Under proper conditions, growth of
casuarina seedlings is extremely rapid, with growth rates of more
than 2 m (6.5 ft) possible the first year. Such rates of growth
are observed only when no competing herbaceous vegetation is
present and may be possible only when the seedlings have been
inoculated with Frankia spp., as noted earlier (11).
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Soils and Topography
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All three Casuarina species prefer coarse-textured soils
of the Entisol, Inceptisol, and Spodosol orders. They show wide
latitude in their soil demands and range from dry, sandy beach
ridges to wet lake margins, but they withstand inundation for
short periods only. In southeastern Florida, the species are
particularly prevalent on alkaline, lime stone-derived soils.
Casuarina equisetifolia is tolerant of very saline conditions
but grows best in slightly acid sandy soils. All three species
tolerate low soil fertility but are quite responsive to
fertilization with phosphorus or nitrogen and phosphorus. They
reach maximum development in slightly depressional topography
where adequate moisture is nearly always available.
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Special Uses
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No commercial use is made of casuarina in Florida, although its
pulping properties are acceptable (5) and reputed to be better
than those of eucalyptus (Eucalyptus spp.) (8). The
species have been widely used for shelterbelts and in landscaping
as hedges and ornamentals (1); C. glauca has been
frequently planted for soil stabilization near drainage ditches
and lakeshores.
The species are well suited for fuelwood because of their fast
growth rates, coppicing potential, and desirable wood properties.
Their wood densities of approximately 0.72 are among the highest
for Florida trees, their green wood moisture content is
relatively low at 60 to 88 percent on an ovendry basis, and their
whole-tree energy values are considerably higher than those of
other species (16). The ash content is slightly higher than that
of most native American woods, averaging about 2 percent; the ash
content of bark is twice this amount. The wood dries rapidly and
burns well. Attempts to saw and season casuarina for use as
lumber have not been satisfactory (10). Casuarina bark has been
used in tanning and medicine, and the fruits have been used for
novelties and decorations (13).
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Vegetative Reproduction
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The three species show different
levels of root suckering: C. glauca root suckers
prolifically; C. cunninghamiana, infrequently; and C.
equisetifolia, not at all. Rooting success, as evidenced by
preliminary trials with fine branches from lower to middle
portions of crowns, is satisfactory for C. cunninghamiana
and C. glauca but low for C. equisetifolia. Use
of rootone and a sand medium typically resulted in rooting as
high as 50 percent in the spring. Grafting appears to be
successful (1).
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Distribution
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Casuarina equisetifolia and C. cunninghamiana
are naturalized to the southwestern and southeastern coastal
areas of Florida as far north as Tampa and Titusville, with
C. equisetifolia particularly prevalent on beaches; C.
glauca is present throughout the same general area,
frequently as very dense stands along roads and fence lines. Casuarina
cunninghamiana exists as planted trees as far north as
Gainesville. In Hawaii, C. equisetifolia is common along
sandy coasts and lowlands (9).
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Brief Summary
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Casuarinaceae -- Casuarina family
D. L. Rockwood, R. F. Fisher, L. F. Conde, and J. B. Huffman
Casuarina species, native to Australia and neighboring
areas, have been introduced into many countries. In the United
States, three species have been established, primarily in Hawaii,
California, and Florida: C. equisetifolia L. ex
J. R. & G. Forst., C. cunninghamiana Miq. and C.
glauca Sieber ex K. Spreng. Other common names of Casuarina
are Australian-pine, beefwood, and horsetail-tree.
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