Australian pine, Casuarina equisetifolia, is not a pine at all. It is a
deciduous dicot angiosperm tree that superficially resembles a conifer
(Division Pinophyta). This tall tree typically possesses a single straight,
rough-barked trunk and an open, irregular crown of branches (Snyder 1992,
Small, round, cone-like fruits and long, whispy, grayish green needle-like
branchlets give the tree its pine-like appearance. Leaves are reduced to small
scales occurring in whorls of 6-8 leaves per whorl at joints (nodes) along the
length of the branchlets. The brown flowers are tiny and non-descript
(Langeland and Burks 1998).
Potentially Misidentified Species
Two congeners, also exotics, occur in Florida. Casuarina glauca
typically grows to 10-15 m with a 0.5 m trunk dbh (diameter at breast height)
and with 10-17 leaf scales per whorl. C. cunninghamiana typically grows to 25 m
with a 0.66 m dbh and 8-10 leaf scales per whorl. Expert examination of the
flowers also reveals that these two species are dioecious (male and female
flowers occur on separate individual organisms). In conrast, C. equisetifolia
is monoecious (male and female flowers on a single individual) and typically
grows to 15-30 m (but can grow taller), with a 0.3-0.5 m dbh and 6-8 leaf
scales per whorl (Snyder 1992, Langeland and Burks 1998). The congeners are
capable of hybridizing, and the presence of hybrids may confound positive
HABITAT AND DISTRIBUTION
The native range of Casuarina equisetifolia includes Malaysia, southern Asia,
Australia and Oceania (the islands of the Pacific between Asia and the
Americas). The worldwide introduced range includes the Caribbean Territories
(including Puerto Rico, and the Bahamas), Hawaii, and coastal Florida (ITIS).
In Florida, the species occurs from north-central Florida southward through the
Australian pine is well established in all six counties of the IRL watershed.
LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan
Australian pine is a fast-growing (1.5-3 m/year) tree that can grow from 20 m to a height of up to 46 m (Swearingen 1997). Elfers (1988) reports the maximum lifespan of Australian pine is 40-50 years.
Australian pine is a Category I exotic species in Florida, indicting it is a
species that has become so abundant that it is altering native plant
communities by displacing native species and changing community structures or
ecological functions (FLEPPC 2005).
Casuarina equisetifolia can reproduce sexually via seed as well as vegetatively
through the sprouting of new clonal trunks from existing rootstock. The
species is monoecious, in contrast to its co-occurring congers in Florida which
Small, inconspicuous flowers are wind pollinated. The up to 3/4 inch oval
cone-like fruits (nutlets) contain approximately 12 rows of seeds when they
mature. Australian pines are capable of flowering for extended periods (even
year-round), and individual trees produce thousands of seeds a year (Morton
1980, Elfers 1988).
Australian pine seeds posses a membranous wing and are readily dispersed by
wind as well as water (Binggeli 1997). Seeds remain viable for up to a year
and will germinate in 4-8 days in porous soil with adequate moisture content
(Elfers 1988). The young seedlings are sensitive to drought and flood and are
also fire-intolerant (Snyder 1992).
C. equisetifolia is a cold-sensitive species and is intolerant to frost (Snyder
1992). Genus Casuarina fares poorly outside of mild temperatures ranging from
22.1 to 26.9°C (Duke 1983).
Although it is a shoreline and coastal tree that is very tolerant to salt
spray, Australian pine fares poorly in sites prone to prolonged inundation of
standing water (Elfers 1988).
Young trees less than 8 cm trunk diameter may resprout following
exposure to fire, but larger trees are usually killed outright (Morton 1980,
Within its native range and in some areas where it has been introduced, Casuarina equisetifolia usually co-occurs with defined community assemblages of lowland
and coastal trees, although it is often the dominant speies (Whistler and Elevitch 2006). In Florida, C. equisetifolia typically competitively displaces
native plant species.
Australian pine reportedly was intentionally introduced to Florida in 1898, as
an ornamental tree and also for use as a windbreak to border agricultural
groves (Morton 1980). In time, the species proved to be ill-suited for either
purpose. The thick, shallow and wide-spreading roots are both disruptive to
lawns and pavement and also make the tree prone to being overblown in strong
winds (e.g., hurricanes). Casuarina equisetifolia grows too tall to be considered a
safe ornamental tree given its tendancy to blow over.
Early on, Australian pine was also utilized in Florida as a a lumber species
and in ditch and canal stabilization (Snyder 1992, Swearingen 1997). It
ultimately proved to be poorly suited to this latter use, again due to its
shallow root system and its tendency to be blown down.
More troubling than its poor utility as a purpose-cultivated species, C.
equisetifolia revealed itself to be a highly invasive species in Florida. The
species' ability to colonize disturbed and nutrient-poor sites, its high fecundity,
protracted reproductive season, broadcast seed dispersal, and tendency to form
monspecific stands are traits that make it a highly competent invader.
Australian pine thrives in subtropical climates within open coastal habitats
such as coastal strand, sand and shell beaches, dunes and rocky shores (Snyder
1992). It is a capable colonizer of newly disturbed sites.
Australian pine is a fast grower that typically forms monospecific stands that
produce a dense shading canopy and also a thick layer of dropped branchlets
('needles') and fruits that blanket the ground below. The roots of C.
equisetifolia harbor nitrogen-fixing microbial assemblages that allow the host
tree to colonize and thrive in low nutrient soil conditions that many other
species cannot tolerate (Swearingen 1997).
Despite an ongoing statewide ban on cultivation, Australian pine is now widely
distributed in central and south Florida. It is also an established exotic
species in California, Arizona, and Hawaii (Snyder 1992). Worldwide, C.
equisetifolia has become broadly established and Duke (1983) notes that it is
one of the most common trees on the upland margins of beaches in frost-free
Two established non-native congeners, Casuarina glauca and C. cunninghamiana
were also introduced to Florida decades ago. In fact, Elfers (1988) reports
that a total of eight nonindigenous Casuarina species were introduced into the
United States prior to 1924.
Potential to Compete With Natives
Australian pine is generally the dominant species in competitive interactions
with native Florida vegetation. Dense thickets of Australian pine can
outcompete and displace mangroves and other native coastal vegetation in
Florida. There is evidence that the fallen branchlets are allelopathic in
nature, containing chemical compounds that inhibit growth, survival, or
recolonization by native plant species.
A monospecific, chemically defended stand of Australian pine offers little in
the way of food or habitat value to native wildlife which are likely to exhibit
reduced abundance and diversity in stands of C. equisetifolia compared to
unaltered stands of native vegetation. Loss of native vegetation reduces
habitat quality for mammals, birds, and other native species.
One of the reasons Australian pine was introduced to Florida was, reportedly,
to serve as a windbreak on exposed shorelines. However, the tree's thick,
shallow roots actually make it more likely to be blown over in high winds than
most coastal native trees. Wind-felled C. equisetifolia can exacerbate erosion
on beaches and dunes and can also act as a physical barrier inhibiting
burrowing by gopher tortoises and beach nesting by endangered sea turtles and
American crocodiles where they occur (Elfers 1988, Moler 1991).
Possible Economic Consequences of Invasion
Potential positive economic uses for Casuarina equisetifolia include use as
windbreaks, landscape trees, lumber, fuel wood, and several other minor uses.
None of these uses are currently pursued in Florida, where a negative
economic impact of the species exists.
The dense roots of C. equisetifolia can disturb pavement and may also
infiltrate and damage water and sewer pipes. Fallen C. equisetifolia can
exacerbate erosion on beaches and dunes, renourishment of which can be both
difficult and expensive (Elfers 1988).
Competitive displacement of coastal mangrove stands by C. equisetifolia can cause
negative economic impacts due to loss of nursery habitat for recreational and
commercial fishing, loss of nesting and roosting habitat for birds, etc.
Inhaled smoke from burning peppers can cause respiratory problems in some people.
All three Casuarina species found in Florida are listed as noxious weeds
(prohibited aquatic plants, Class 1) (Elfers 1988, Snyder 1992, FLEPPC. 2005).
Binggeli P. 1997. Casuarina equisetifolia L. (Casuarinaceae), Woody
Plant Ecology. Available online.
Duke J.A., 1983 Casuarina equisetifolia J.R. and G. Forst., Center for
New Crops and Plant Products, Purdue University.
Elfers S.C. 1988. Element Stewardship Abstract for Casuarina
equisetifolia. The Nature Conservancy. Unpublished report prepared for The
Nature Conservancy on Australian pine. Winter Park, FL.
FLEPPC. 2005. List of Florida's Invasive Species. Florida Exotic Pest Plant
Langeland K.A., and K.C. Burks (Eds.). 1998. Identification and Biology of
Non-Native Plants in Florida's Natural Areas. UF/IFAS. 165 p.
Moler P.E. 1991. American crocodile nest survey and monitoring. Final Report to
Study No. 7533, Florida Game and Fresh Water Fish Commission, Bureau of
Wildlife Research, Tallahassee FL.
Morton J.F. 1980. The Australian pine or beefwood (Casuarina
equisetifolia L.), an invasive "weed" tree in Florida. In:
Proceedings,Florida State Horticultural Society 93:87-95.
Snyder S. A. 1992 SPECIES: Casuarina spp., U.S. Department of
Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences
Laboratory, Fire Effects Information System.
Swearingen J.M. 1997. Australian Pine. Washington, D.C. National Park Service,
Plant Conservation Alliance, Alien Plant Working Group. Available online.
Whistler W.A., and C.R. Elevitch. 2006 Casuarina equisetifolia (beach
she-oak), C.cunninghamiana (river she-oak); Casuarinaceae (casuarina
family). Species profiles for Pacific Island agroforestry ecological, economic,
and cultural renewal. Available online.