Taxonomic name: Casuarina equisetifolia L.
Synonyms: Casuarina litorea L. var. litorea, Casuarina litorea Rumpheus ex
Stickman, Casuarina littorea L. ex Fosberg & Sachet
Common names: agoho (Philippines), arbol de hierro (Spanish-Galapagos), Australian beefwood (English), Australian-pine (English), beach she-oak (English), beef wood-tree (English), bois de fer (French), casuarina, coast she-oak (English), Eisenholz (German), filao (French), horsetailtree (English), ironwood (English), nokonoko (Fiji), pin d'Australie (French), pinheiro-da-Austrália (Portuguese), pino australiano (Puerto Rico), Strandkasuarine (German), whistling-pine (English)
Organism type: tree
Casuarina equisetifolia is an evergreen conifer-like angiosperm. It has been introduced to new locations for coastal landscaping and erosion control. It has become invasive in Florida (USA) where it interferes with prime reptile nesting sites. Casuarina aggressively colonizes sandy beaches where it forms monocultures and degrades habitat in the Cayman Islands.
Casuarina equisetifolia is a member of the Casuarinaceae (beefwood) family; it is an evergreen tree with a soft wispy pine-like appearance and an open irregular crown (FEPPC Undated). The tree can attain heights of up to 50 meters, with a diameter of up to 18 centimetres; however, it generally only reaches 15 to 25 meters in height (NRC US Advisory Committee on Technology Innovation 1980). It bears a resemblance to coniferous plants due to the production of cone-like fruits and pine-needle-like leaves.
It has reddish brown to grey bark; the bark is rough, brittle, peeling. Branchlets are pine-needle like, greyish green, jointed, thin (less than 1 millimetre wide), 10 to 20 centimetres (four to eight inches) long, minutely ridged, hairy in furrows. Leaves are reduced to tiny scales, six to eight in whorls (this is a distinguishing feature, see Similar Species), whorls encircle joints of branchlets. Flowers are unisexual/monoecious, inconspicuous, female in small axillary clusters, male in small terminal spikes. Fruit is a tiny, one-seeded, winged nutlet (samara), formed in woody cone-like clusters (fruiting heads), these clusters are brown, two-centimetre-long (3/4 inch) and 1.3 centimetre-wide (1/2 inch) (Description from FEPPC Undated).
Casuarina cunninghamiana, Casuarina glauca
coastland, estuarine habitats, riparian zones, ruderal/disturbed
Casuarina equisetifolia occurs in open coastal strand habitats in subtropical and tropical climates, including: sandy and shelly beaches, rocky coasts, sand dunes, sand bars and estuarine/mangrove habitats (NRC US Advisory Committee on Technology Innovation 1980; Swearingen 1997; DaCosta-Cottam et al. 2009). Its natural habitat has been described as coastal herbaceous swamp and broad-leaved hammock communities (Binggeli 1997), however, C. equisetifolia frequently colonises disturbed sites such as filled wetlands, roadsides and cleared land (Elfers 1988).
This rapid-growing species will establish in habitats as varied as coastal sand dunes, high mountain slopes, the humid tropics and semiarid regions; it tends to be salt tolerant, wind resistant and adaptable to moderately poor solids; although it is not a legume it does have the ability to form root nodules with microbial associations and fix atmospheric nitrogen (NRC US Advisory Committee on Technology Innovation 1980; Little & Skomen 1989, in Snyder 1992).
The monthly mean maximum temperature in the native area of Casuarina is 10°C to 33°C and it is reported to prefer annual temperatures of 22°C to 27°C; it is not frost-hardy (NRC US Advisory Committee on Technology Innovation 1980; Duke 1983; Snyder 1992). This lowland species grows from sea level up to 1 500 meters; in its natural habitat rainfall is from 700 to 2 000 millimetres, often with a dry season of six to eight months; however, it is reported to tolerate an annual precipitation of 640 to 4 300 millimetres (NRC US Advisory Committee on Technology Innovation 1980; Duke 1983).
This species tolerates calcareous (limestone-derived) and slightly saline soils with a pH of between 5.0 and 7.7 but it grows poorly on heavy soils such as clays; it can withstand partial water-logging for a time (NRC US Advisory Committee on Technology Innovation 1980; Duke 1983). It is reported to prefer coarse-textured soils (Rockwood et al undated) and is very tolerant of saline conditions and salt spray (Elfers 1988).
Casuarina equisetifolia is a fast-growing plant which produces heavy shade and a thick blanket of leaves and fruits beneath it, reducing habitat value (Florida DEP Undated). Its dense monoculture thickets displace native dune and beach plant species. Once established, C. equisetifolia alters light, temperature, soil chemistry and hydrology of the habitats it invades.
Habitat alteration: The thick layer of leaves produced by C. equisetifolia has a reduced food value for native wildlife and destroys habitat for native insects and other wildlife (Klukas 1969, in Snyder 1992).
Reduction in native biodiversity: C. equisetifolia forests provide little or no native wildlife habitat. In the Everglades, where C. equisetifolia has invaded south Florida’s hammock and tree island communities, Mazzotti Ostrenko and Smith (1981) studied the effects of Melaleuca quinquenervia and C. equisetifolia on three native rodents (Peromyscus gossypinus, Sigmodon hispidus and Oryzomys palustris). The authors found that Casuarina habitats supported fewer rodents than either cocoplum or Melaleuca habitats.
Threat to endangered species: C. equisetifolia displaces native beach vegetation that provide critical wildlife habitat for threatened and endangered plant and animal species. C. equisetifolia forms dense stands and destroys reptile breeding sites in the Everglades National Park. Its presence threatens the only remaining nesting areas in the USA of the ‘Vulnerable (VU) American crocodile (Crocodylus acutus) and one of the remaining most productive nesting areas of the ‘Endangered (EN)’ loggerhead turtle (Caretta caretta ssp. caretta)) and the ‘Endangered (EN)’ green turtle (Chelonia mydas) (Binggeli 1997; Klukas 1969 1973, in USDA Forest Service 2007). The nest sites of these species are threatened as the invasive plant takes over beach dune habitat and baby sea turtles become trapped in its roots as they emerge from their nests (Florida DEP Undated). Areas inhabited by the ‘Vulnerable (VU) gopher tortoise (Gopherus polyphemus) are also threatened with invasion by Casuarina (Mazzotti Ostrenko and Smith 1981).
Modification of hydrology: C. equisetifolia can exhaust the moisture in the soil and lower the water table of the area (NRC US Advisory Committee on Technology Innovation 1980) it invades.
Physical disturbance: C. equisetifolia can facilitate beach erosion by displacing deep-rooted vegetation (Florida DEP Undated). Unlike native vegetation C. equisetifolia has a shallow root system and tends to uproot and topple during high winds, posing a significant hazard to coastal storm evacuation routes (Florida DEP Undated). Its dense roots can also break water-lines and sewer-lines (Snyder 1992).
Inhibits the growth of other species: C. equisetifolia produces allelopathic compounds that inhibit growth of other plants (Morton 1980, in Florida DEP Undated).
Modification of successional patterns: C. equisetifolia can be a primary or secondary coloniser in disturbed areas in Florida, USA (Elfers 1988, Klukas 1969, in Snyder 1992).
Human health: The genus Casuarina poses a problem to humans as its pollen is a source of respiratory irritation and allergies (Elfers 1988; Binggeli 1997).
Casuarina is widely planted for coastal reclamation, erosion control, tannin, pulp, timber and fuel, the latter particularly in third world countries (Duke 1983; Elfers 1988). Casuarina was once used in the USA for reclaiming eroded areas, but many land managers condemn its use because it threatens indigenous plants and animals (Little & Skomen 1989, in Snyder 1992). Some African and Asian countries use it to combat desertification (Vietmeyer 1986, in Snyder 1992).
The wood is used for beams, boat building, electric poles, fences, furniture, mine props, oars, pavings, pilings, roofing shingles, tool handles, wagon wheels and yokes (Elfers 1988, Little & Skomen 1989, in Snyder 1992). Hill tribes of New Guinea use Casuarina in rotation to restore nitrogen to the soil. The leaves have been employed in preparing active carbon by the zinc chloride method. Minor uses include wood ash for making soap and the extraction of dye from its bark (Elfers 1988). Casuarina species have medicinal value; the astringent bark extract may be used as a remedy for diarrhea and dysentery and to help relieve a sore throat.
Casuarina cunninghamiana Miq. (River sheoak), C. equisetifolia L. (Australian pine) and C. glauca Seiber (gray sheoak) hybridise with each other (Morton 1980, in Snyder 1992; all three pose a threat to the environment and are considered invasive in the USA (Flores 2008).
There are two subspecies: C. equisetifolia var. equisetifolia and C. equisetifolia var. incana Benth; they differ in height and stem straightness, the latter has a smaller and poorer stem form and a more open canopy; many morphological features are variable (Binggeli 1997).
Native range: Casuarina equisetifolia is native to Malaysia, Southern Asia, and Oceania (Swearingen 1997).
Known introduced range: C. equisetifolia is introduced in Hawaii, Mexico, south and central Florida, Puerto Rico, the Bahamas, many other Caribbean islands and elsewhere in the tropics (Florida DEP Undated). It is now one of the most common trees on frost-free beaches world-wide (Duke 1983).
Introduction pathways to new locations
Landscape/fauna "improvement": C. equisetifolia was introduced into Florida in the late 1800s, planted widely for the ditch and canal stabilization, shade and timber (Swearingen 1997).
People sharing resources: Seven Australian and one East Indian species of the genus Casuarina were introduced into the United States before 1924, beginning with seeds brought from France in 1898 by the U.S. Dept. of Agriculture explorer, Dr. W. T. Swingle. Some seeds were distributed under erroneous names and problems of misidentification have continued since (Elfers 1988).
Local dispersal methods
Consumption/excretion: The seeds are dispersed by birds (especially exotic parrots and parakeets) (Morton 1980, in Florida DEP Undated).
On animals (local): The seeds reportedly get stuck and transported on animals.
Water currents: Fruiting heads float (Maxwell 1984, in Florida DEP Undated) and the seeds can be dispersed in rivers and the sea (Binggeli 1997; Burton 2003 in Varnham 2006).
Wind dispersed: The seeds have membranous wings and are wind-dispersed (Binggeli 1997).
Preventative measures: A Risk Assessment of C. equisetifolia for Hawaii and other Pacific islands was prepared in 2008. The result is a score of 21 placing it in the High Risk category and concluding that it is "likely to cause significant ecological or economic harm in Hawaii and on other Pacific Islands".
Physical: For small infestations the manual removal of seedlings and saplings is recommended (Swearingen 1997); however, it should be noted that cutting often induces sprouting (Snyder 1992).
Prescribed fire has been used for large infestations in fire-tolerant vegetation communities. Fire control is reported to be effective in dense stands with sufficient dry fuel on the ground. Periodic fires coupled with the use of herbicides may be an effective method of controlling Casuarina (Snyder 1992). However, too frequent intense fires that kill over story native pines may actually encourage Casuarina species to establish (Wade Ewel & Hofstetter 1980, in Snyder 1992). Burning Casuarina in peat soils may be hazardous (Morton 1980, in Snyder 1992). Fire may be an effective control method for trees greater than eight centimetres (three inches) in diameter and in dense stands; burning could be potentially harmful if the soil pH is changed such that native species cannot establish (Elfers 1988, in Snyder 1992).
Chemical: For heavier infestations application of a systemic herbicide to bark, cut stumps or foliage is likely to be most effective. Chemicals such as 2,4,5-T, 2,4-D or Garlon 3A can be used to tackle Casuarina (Klukas 1969, Morton 1980, in Snyder 1992). A 2% mixture of Garlon 4 in diesel oil applied using the basal bark method or the hack-and-squirt method is most commonly used against Casuarina in the USA (US Exotic Pest Plant Council Undated). Garlon 3A is also effective.
Biological: USDA Agricultural Research Service (ARS) scientists have been searching in Australia's outback and coastlines for insects that could be key bio-controls for C. equisetifolia (Flores 2008). From 300 species, including wasps, weevils, stem-borers, sap-suckers and seed-eaters about 12 candidates have been identified. Not only do these agents attack C. equisetifolia but many also attack the related invasives C. glauca and C. cunninghamiana. The most promising bio-control agents include the seed-feeding wasp (Bootanelleus orientalis), which is host-specific to Australian pine, and the defoliator moth (Zauclophora pelodes). These insects are still undergoing testing to determine their suitability for use as bio-control agents in the United States. Please follow this link to read more about this research in the September 2008 issue of Agricultural Research magazine.
Many pathogens threaten plantations of Casuarina in many parts of the world. In India a stem borer kills shoots and seedling damping-off by Rhizoctonia spp. occurs in nurseries (Binggeli 1997). Nursery seedlings in India are attacked by various insect species. In China the lymantriid moth (Lymantria xylina) is described as one of the worst pests of C. equisetifolia (Elfers 1988).
In Florida, USA, there has been a high rate of root rot caused by the fungus Clitocybe tabescens. In Puerto Rico stem canker and dieback attributable to the fungus Diplodia natalensis have been recorded on C. equisetifolia. In Puerto Rico natural regeneration is rare because ants eat nearly all the seeds (Binggeli 1997). Ants have also reportedly been a major source of control in India.
Integrated Pest Management: Recently disturbed beach habitat may be planted with native vegetation to prevent C. equisetifolia from invading.
Casuarina equisetifolia can tolerate low soil fertility but is quite responsive to fertilisation with phosphorus or nitrogen and phosphorus (Rockwood et al. UNDATED).
Casuarina equisetifolia produces thousands of wind-dispersed winged seeds per plant and resprouts profusely following coppicing (Elfers 1988). A single four or five year-old tree can produce thousands of seeds (Elfers 1988). Seeds in the seed bank can remain fertile for a few months to a year and germinate under conditions of adequate moisture and porous soil in four to eight days (Snyder 1992).
C. equisetifolia flowers and fruits year-round in warm climates (Elfers 1988, in Snyder 1992). In the USA C. equisetifolia usually flowers and fruits twice a year: between February and April, and September and October, producing fruit in June and December. In Hawaii and Puerto Rico flowering and fruiting times are irregular (Binggeli 1997).
Young seedlings are sensitive to drought, flood and fire. Growth is most rapid during the first 7 years. The minimum seed-bearing age is 4 to 5 years. Maximum growth is reached in 20 years with a maximum life span of 40 to 50 years (Elfers 1988, in Snyder 1992). In Florida, growth rates have ranged from 0.5 to 1.5 metres per year under stressed conditions and over 3 metres per year under cultivation.
Reviewed by: Kenneth Langeland Professor, Extension Specialist, Agronomy. Center for Aquatic and Invasive Plants. Florida USA.
Compiled by: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
Updates under progress with support from the Overseas Territories Environmental Programme (OTEP) project XOT603, a joint project with the Cayman Islands Government - Department of Environment
Last Modified: Saturday, 23 January 2010