2993

11: Auxiliary plants

Casuarina equisetifolia L.

Amoen. Acad. 4: 143 (1759).

CASUARINACEAE

2n = 18, (20)

Casuarina litorea L. (1759), Casuarina equisetifolia J.R. & G. Forster (1776).

Coast she-oak, ironwood, whistling pine (En). Beach she-oak (Am). Filao (Fr). Indonesia: cemara laut, eru. Malaysia: ru laut. Papua New Guinea: yar. Philippines: Australian pine, agoho. Burma (Myanmar): tin-yu. Cambodia: snga:w. Laos: pè:k namz, sôn th'ale:. Thailand: son-thale (general). Vietnam: c[aa]y phi lao.

Casuarina equisetifolia has the widest natural distribution of all Casuarina species, occurring naturally along the tropical coastlines from northern Queensland and the Northern Territory in Australia, throughout the whole Malesian region to the Kra Isthmus (Thailand). To the east its natural range extends throughout Melanesia and Polynesia. It is doubtfully indigenous to the Mekong Delta in Vietnam and to Burma (Myanmar) and possibly also to Madagascar. It has also been introduced into a large number of countries and is now a common feature of the coastal landscape of most tropical and warm subtropical countries, where it is often naturalized.

The most common uses of Casuarina equisetifolia are for coastal sand dune stabilization, shelter-belts, land reclamation and erosion control. It is a popular agroforestry tree in coastal and saline areas. In Sarawak it is protected because of its importance in controlling coastal erosion. Many areas of occurrence are susceptible to tropical cyclones or typhoons and Casuarina equisetifolia's general tolerance to strong winds has encouraged its use in protective plantings. A 3000 km long belt along the coast of southern China is planted to Casuarina equisetifolia for this purpose.
The wood is highly regarded as a fuel. It burns even when green and produces high quality charcoal. The small branch litter is often collected for domestic fuel and is sometimes used to fuel pottery and brick kilns. Poles are popular as masts for fishing boats, piles, posts and tool handles. Sawn timber is only used for small items like roofing shingles. The wood is used to produce paper pulp using neutral sulphate and semi-chemical processes and as raw material for rayon fibres. In Egypt it is used to make chipboard.
The bark has been used for tanning and is still occasionally used by amateur tanners. Medicinal use is made of the roots to treat dysentery, diarrhoea and stomach ache. In West Malaysia, a decoction of the twigs is used for treating swellings and the powdered bark is used for treating facial pimples.

No statistics are available on production and trade.

The bark of Casuarina equisetifolia is astringent and contains 6—18% tannins. Tests of the chemical composition of the branchlets in Puerto Rico gave per 100 g dry matter: N 1.56 g, P 0.16 g, K 0.48 g, Ca 1.23 g, Mg 0.23 g, Na 3.28 g.
The wood is hard and heavy with an air-dry density of 900—1000 kg/m³, sapwood being slightly heavier than heartwood. Green logs have a moisture content of 40—60%. The energy value of the wood is 24*000 kJ/kg and that of the charcoal exceeds 33 500 kJ/kg. The wood produces little ash and burns even when green. On sawn timber the rays are prominent on radial faces. The wood tends to warp and crack on drying.
The weight of 1000 seeds is 1.4—3.3 g.

Monoecious tree with a finely branched crown, 6—35 m tall, with trunk diameter up to 50 cm; bark light greyish-brown, smooth on young trunks, rough, thick, and furrowed on older trees; inner bark reddish and astringent; branchlets deciduous, drooping, needle-like, terete but with prominent angular ribs, 23—38 cm x 0.5—1 mm, greyish-green, articles 5—8 mm long, glabrous to densely pubescent. Leaves reduced to minute teeth, in whorls of 7—8 per node. Male flowers in a terminal, simple, elongated spike, 7—40 mm long, borne in whorls with 7.0—11.5 whorls per cm of spike. Female inflorescence on lateral woody branches, cylindrical, cone-shaped or globose, 10—24 mm long, 9—13 mm in diameter; bracteoles acute, more or less protruding from the surface of the cone. Fruit a samara, 6—8 mm long, 1-seeded, dull brown. Seed with epigeal germination.

Casuarina equisetifolia has a life span of 40—50 years and displays fast early growth. Under favourable conditions early growth in height may exceed 3 m per year. At 10 years a height exceeding 10 m and a diameter of 20 cm may be reached.
Branching in Casuarinaceae is dimorphic. Most prominent are the green needle-twigs that are functional leaves with a limited life and determinate growth. With age they turn brown and are shed. The other type of branch is normal, woody, with indeterminate growth.
Tree form in wild populations is very variable, from crooked low-branching trees on exposed seashores to straight-stemmed forest trees with a narrowly conical crown in more sheltered situations and in plantations. Casuarina equisetifolia coppices only to a limited extent and only when cut young (3—4 years).
Although trees in natural stands are mostly monoecious, many introduced populations are dioecious. Pollination is by wind. Female cones mature about 18—20 weeks after flowering, and open shortly thereafter, releasing the small winged fruitlets.
Casuarina equisetifolia forms large, long-lived, woody root nodules with several strains of the actinorhizal symbiont, Frankia, which enables it to fix atmospheric nitrogen. These root nodules can be prolific. Extrapolations from experimental data indicate that 90 kg/ha of atmospheric nitrogen can be fixed annually at a planting density of 2000 trees per ha. Uptake of other plant nutrients is enhanced by the presence of proteoid roots and associations with ectomycorrhizal and endomycorrhizal fungi. As in other actinorhizal plants, endomycorrhizal (VAM) infection occurs easily.

Linnaeus's publication of Casuarina equisetifolia consists only of a name and a reference to a drawing by Rumphius. Unfortunately, the name contains a printing error (equisefolia) and many sources therefore cite J.R. & G. Forster as the original authors. Correction of the typographical error is allowed, however.
In Casuarina equisetifolia two subspecies have been distinguished: subsp. equisetifolia is most common and most widely distributed; subsp. incana (Benth.) L.A.S. Johnson occurs exclusively along the coast of Queensland and northern New South Wales and on Vanuatu. It is a 6—12 m tall tree with densely pubescent immature branchlets with sometimes flat and wrinkled ribs.

Casuarina equisetifolia is commonly confined to a narrow strip adjacent to sandy coasts, usually from sea level to 100 m altitude, but recorded to 600 m in Hawaii and 800 m in the Philippines. It is planted up to 1200 m altitude. It is found on sand dunes, in sands alongside estuaries behind foredunes and gentle slopes near the sea. It may be found at the leading edge of dune vegetation, subjected to salt spray and inundation with sea water at extremely high tides and where it may be the only woody species, growing over a ground cover of dune grasses and salt-tolerant broad-leaved herbs. It may also be part of the richer Indo-Pacific beach flora, in which it grows in association with Barringtonia asiatica (L.) Kurz, Calophyllum inophyllum L., Heritiera littoralis Aiton, Hibiscus tiliaceus L., Thespesia populnea Sol. ex Correa and Pandanus species. It requires much light. Seedlings do not grow in the shade of uniform Casuarina equisetifolia stands and such stands are gradually replaced by mixed forest, with a single file of Casuarina equisetifolia trees along the sea front.
The climate in its natural range is semi-arid to sub-humid and frost-free. Rainfall varies from 700—2000(—3500) mm per year. In most regions there is a distinct dry period of 4—6(—8) months, although this seasonality decreases towards the equator in South-East Asia and in the southern parts of its range in Australia. Casuarina equisetifolia is intolerant of prolonged waterlogging. It can grow in semi-arid climates with annual rainfall of less than 350 mm where sea spray and high air humidity supplement rainfall. Mean minimum temperature of the coldest month ranges from 7°C—20°C, mean maximum temperature of the hottest month from 20°C—35°C.
Soils are invariably well-drained and rather coarse-textured, principally sands and sandy loams. The tree tolerates saline, calcareous and slightly alkaline soils and is very well adapted to soils of low fertility.

Propagation is mainly by seed, although cuttings are increasingly used. Seed requires no pretreatment. Germination takes up to two weeks. In Thailand and India cuttings are made from small branchlets 10—15 cm long and 2 mm in diameter. Rooting is enhanced through use of the hormones indole-3-butyric acid (IBA) or indole-3-acetic acid (IAA). In southern China cuttings are taken from branchlets of 5 cm long and 1 mm in diameter and soaked in a solution of naphthalene-1-acetic acid (NAA) before being placed in polythene bags.
Inoculation of the seedlings with a pure culture of effective strains of Frankia is recommended when Casuarina equisetifolia is introduced to a new area. This is done by applying a water suspension of the inoculant to the seedlings. Applying a solution of crushed nodules works less well. The availability of mycorrhizal fungi can be assured by adding soil collected from established stands to the potting medium. Early growth can be doubled as a response to inoculation.
Plantations can be established using containerized seedlings, bare-root seedlings or rooted cuttings. Plants are typically suitable for planting out when 25—30 cm tall, though in the desert climate of Egypt smaller seedlings are preferred. A density of 2500 plants per ha is commonly used, but some private farmers plant up to 8000—10 000 plants per ha. Young trees compete poorly with weeds, so weeding is important for 2 years after planting.

Casuarina equisetifolia is considered to be a poor self pruner. Pruning in plantations is necessary up to 2 m, to keep plantations accessible for general maintenance. Pruning may, however, allow infection with fungal pathogens, especially Trichosporium vesiculosum. Casuarina equisetifolia is not fire-resistant and protection is necessary, even against light fires. Leaf litter from plantations is frequently removed for fuel; this depletes the soil's reserves of phosphorus and potassium.

Casuarina equisetifolia is only rarely attacked by diseases and pests except when grown under unfavourable conditions. The most serious disease threatening Casuarina equisetifolia plantations is blister blight caused by the fungus Trichosporium vesiculosum. Infected trees exhibit symptoms of foliar wilt and cracking of the bark, where blisters develop enclosing a black powdery mass of spores. Bacterial wilt disease caused by Pseudomonas solanacearum, characterized by yellowing of the foliage followed by wilting and death, has been reported in China and India. Other potentially serious diseases include stem canker and dieback caused by Phomopsis casuarinae and pink disease (Corticium salmonicolor).
In the nursery and in newly-established plantations, seedlings are sometimes attacked by termites, crickets or rodents. Young trees may be seriously damaged by browsing animals.

Rotation periods vary from 6—15 years when harvesting for fuelwood.

On favourable sites, Casuarina equisetifolia can reach an annual increment of 15 m³/ha at 10 years. In India, plantations using 1—2 m x 1—2 m spacing on 6—15 year rotations yield 50—200 t of wood per ha. Dry weight of stems, branches and twigs per tree ranges from 15 to 25 kg at 3 years of age, depending on site quality. Up to 4 t/ha of litter and twigs may be harvested for fuel.

The Australian Tree Seed Centre of the Division of Forestry and Forest Products of the Commonwealth Scientific and Industrial Research Organization (CSIRO) has a collection of seed material collected from 65 sites in 21 countries. International trials to evaluate this material are under way on about 30 sites in 20 countries and are being coordinated by the Australian Tree Seed Centre. The large phenotypic variation displayed between populations can be exploited for tree improvement. The effectiveness of different Frankia strains varies greatly. Frankia collections are maintained by the Office de la Recherche Scientifique et Technique d'Outre-Mer (ORSTOM) in France, the CSIRO Division of Soils in Townsville, Australia and at the School of Forestry at Yale University, Cambridge, United States.

Considerable improvements in growth following conventional plant breeding and screening of élite trees followed by vegetative propagation are anticipated.

Casuarina equisetifolia will remain of considerable importance for agroforestry and reclamation of unstable coastal ecosystems in tropical countries. Improvement by breeding and concurrent screening of Frankia and mycorrhiza strains for effectiveness will receive priority.

Dommergues, Y., 1990. C. equisetifolia: An old-timer with a new future. Nitrogen Fixing Tree Association. NFT Highlights 90-02. 2 pp.
El-Lakany, M.H., Turnbull, J.W. & Brewbaker, J.L. (Editors), 1990: Advances in Casuarina research and utilisation. Proceedings of the Second International Casuarina Workshop, January 15-20, 1990, Cairo. Desert Development Centre, American University in Cairo, Cairo, Egypt. 241 pp.
Midgley, S.J., Turnbull, J.W. & Johnston, R.D. (Editors), 1983. Casuarina ecology, management and utilization. Proceedings of an International Workshop, 17-21 August 1981, Canberra, Australia. Commonwealth Scientific and Industrial Research Organization (CSIRO), Melbourne, Australia. 286 pp.
Pinyopusarerk, K., 1993. Casuarina: an annotated bibliography of C. equisetifolia, C. junghuhniana and C. oligodon. International Centre for Research in Agroforestry (ICRAF), Nairobi, Kenya. 298 pp.
Pinyopusarerk, K., Turnbull, J.W. & Midgley, S.J. (Editors), 1996. Casuarina research and development. Proceedings of the Third International Casuarina Workshop, 4-7 March, 1996. Da Nang, Vietnam and CSIRO, Australia.
Wilson, K.L. & Johnson, L.A.S., 1989. Casuarinaceae. Flora of Australia. Vol. 3. Bureau of Flora and Fauna, Australian Government Publishing Service, Canberra, Australia. pp. 100-106.

S.J. Midgley & R. Sylvester

Midgley, S.J. & Sylvester, R., 1997. Casuarina equisetifolia L.. In: Faridah Hanum, I & van der Maesen, L.J.G. (Editors): Plant Resources of South-East Asia No 11: Auxiliary plants. PROSEA Foundation, Bogor, Indonesia. Database record: prota4u.org/prosea