Arundo donax (Giant Reed)

Scientific name

Arundo donaxL.

Synonyms

Aira bengalensis (Retz.) J.F. Gmel.; Amphidonax bengalensis (Retz.) Nees ex Steud.;  Arundo aegyptiaca hort ex. Vilm.

Common names

Giant reed, Spanish reed

Family

Poaceae (Gramineae)

Origin

Arundo donax is native to eastern and southern Asia, and probably also parts of Africa and the southern Arabian Peninsula.

Naturalised distribution (global)

Locations within which Arundo donax is naturalised include Mediterranean countries, California, and many islands in the Pacific Ocean and the Caribbean.

Introduced, naturalised or invasive in East Africa

Arundo donax is invasive in parts of Tanzania (Henderson 2002), has been introduced to Kenya and is naturalised in parts of Tanzania and Uganda (A.B.R. Witt pers. obs.).

Habitat

Arundo donax forms dense stands on disturbed sites, sand dunes, in wetlands and in riparian zones (banks of watercourses).

Description

Arundo donax is a grass that generally grows to 6 m high, in ideal conditions it can exceed 10 m, with hollow stems 2 - 3 cm diameter. The leaves are alternate, 30 - 60 cm long and 2 - 6 cm  wide with a tapered tip, grey-green, and have a hairy tuft at the base. Overall, it resembles an outsize Phragmites australis (common reed) or a bamboo (Subfamily Bambusoideae). A. donax flowers bear upright, feathery plumes 40 - 60 cm long, but the seeds are rarely fertile.

Reproduction and dispersal

Arundo donax reproduces vegetatively, by underground rhizomes. The rhizomes are tough and fibrous and form knotty, spreading mats that penetrate deep into the soil up to 1 m deep. Stem and rhizome pieces less than 5 cm long and containing a single node readily sprouted under a variety of conditions (Scott 1994)). This vegetative growth appears to be well adapted to floods, which may break up individual A. donax clumps, spreading the pieces, which may sprout and colonise further downstream (Tu et al. 2001). It flowers but does not produce viable seed.

Similar species

Arundo donax may be easily confused with Phragmites australis (common reed) and Pennisetum purpureum (elephant grass). These species can be distinguished by the following differences:

  • Arundo donax is a very tall grass (2-7 m tall) with relatively broad leaves (10-80 mm wide). Its much-branched feathery seed-heads (open panicles) are usually whitish in colour when mature.
  • Phragmites australis is a relatively tall grass (1.5-3 m tall) with relatively narrow leaves (10-35 mm wide). Its much-branched feathery seed-heads (open panicles) are usually light brown when mature.
  • Pennisetum purpureum is a very tall grass (1-6 m tall) with relatively narrow leaves (20-40 mm wide). Its spike-like bristly seed-heads (spiciform panicles) are straw-coloured when mature.

A. donax is also quite similar to Phyllostachys aurea (golden bamboo), Phyllostachys nigra (black bamboo), Arundinaria simonii forma variegata (arundinaria reed) and other bamboo species (e.g. Bambusa spp.). However, all these species can be distinguished from A. donax by the presence of a strongly constricted lower leaf blade, which resembles a short leaf stalk (a pseudo-petiole). In contrast, A. donax has a relatively broad leaf blade base with a membranous ligule.

Economic and other uses

Arundo donax is widely cultivated as an ornamental grass. A form with variegated leaves (Arundo donax var. versicolor) is still very common in cultivation. It is being increasingly promoted as a biofuel feedstock. It is also used for building material.

Environmental and other impacts

Arundo donax is regarded as an environmental weed in many parts of the world. It is invasive in parts of South Africa, Australia, and the USA, particularly in Florida and California, where it is a problem in riparian zones (banks of watercourses) and along roadsides. In densely infested areas it has replaced native plants along rivers, such as willows and cottonwoods, thereby interfering with water flow and displacing riverside habitat. Colonies of A. donax covering hundreds of acres have been recorded. It is highly flammable and can change fire regimes in invaded areas, thereby transforming riparian communities of native plants into solid stands of this species.

A. donax has been nominated as among 100 of the "World's Worst" invaders by the IUCN Invasive Species Specialist Group and it has been listed as a noxious weed in South Africa (prohibited plants that must be controlled. They serve no economic purpose and possess characteristics that are harmful to humans, animals or the environment) and in the Australian state of New South Wales.

Management

The precise management measures adopted for any plant invasion will depend upon factors such as the terrain, the cost and availability of labour, the severity of the infestation and the presence of other invasive species. Some components of an integrated management approach are introduced below.

The best form of invasive species management is prevention. If prevention is no longer possible, it is best to treat the weed infestations when they are small to prevent them from establishing (early detection and rapid response). Control is generally best applied to the least infested areas before dense infestations are tackled. Consistent follow-up work is required for sustainable management.

Stems can be manual removed using a combination of cutting stems and digging up roots with shovel or pick axe. Prescribed burning can also be used as a control method but it does not remove underground stems and roots and may cause damage to native species. Suitable herbicides can be applied as a foliar spray (most effective when applied after flowering or as a concentrated solution applied directly to freshly cut stems. When using any herbicide always read the label first and follow all instructions and safety requirements. If in doubt consult an expert.

Grazing by cattle, sheep and goats and wild animals can reduce the biomass of plant but it does not eliminate underground stems and roots.

There has been some research on biocontrol options for this species (CABI Invasive Species Compendium) but agents have not been released.

Legislation

Not listed as a noxious weed by the state or governments in Kenya, Tanzania and Uganda.

Notes

Arundo donax has been cultivated throughout Asia, southern Europe, northern Africa, and the Middle East for thousands of years. Ancient Egyptians wrapped their dead in the leaves. The canes contain silica, perhaps the reason for their durability, and have been used to make fishing rods, and walking sticks.

The stem material is both strong and flexible. It is the principal source material for reeds for woodwind instruments such as the oboe, bassoon, clarinet, and saxophone. It is also often used for the chanter and drone reeds of many different forms of bagpipes. A. donax has been used to make flutes for over 5,000 years. The pan pipes consist of ten or more reed pipes. Its stiff stems are also used as support for climbing plants or for vines.

References

CABI invasive species compendium online data sheet. Arundo donax (giant reed). CABI Publishing 2011. www.cabi.org/ISC. Accessed August 2011.

GISD (2011). Global Invasive Species Database online data sheet. Arundo donax. www.issg.org/database. Accessed March 2011.

Henderson, L. (2001).  Alien weeds and invasive plants. A complete guide to declared weeds and invaders in South Africa.  Plant Protection Research Institute Handbook No. 12, 300pp. PPR, ARC South Africa.

Henderson, L. (2002). Problem plants in Ngorongoro Conservation Area. Final Report to the NCAA.

Henderson, L. and Cilliers, C.J. 2002. Invasive aquatic plants-a guide to the identification of the most important and potentially dangerous invasive aquatic and wetland plants in South Africa. PPRI Handbook No. 16, Agricultural Research Council, Pretoria.www.arc.agric.za/uploads/images/0_SAPIA_NEWS_No._17.pdf.

Scott, G. (1994). Fire threat from Arundo donax. pp. 17-18 in: November 1993 Arundo donax workshop proceedings, Jackson, N.E. P. Frandsen, S. Douthit (eds.). Ontario, CA.

Tu, M., Hurd, C., and Randall, J.M. (2001). Weed Control Methods Handbook: Tools and Techniques for Use in Natural Areas. The Nature Conservancy.

Editors

Agnes Lusweti, National Museums of Kenya; Emily Wabuyele, National Museums of Kenya, Paul Ssegawa, Makerere University; John Mauremootoo, BioNET-INTERNATIONAL Secretariat - UK.

Acknowledgments

This fact sheet is adapted from The Environmental Weeds of Australia by Sheldon Navie and Steve Adkins, Centre for Biological Information Technology, University of Queensland. We recognise the support from the National Museums of Kenya, Tropical Pesticides Research Institute (TPRI) - Tanzania and Makerere University, Uganda. This activity was undertaken as part of the BioNET-EAFRINET UVIMA Project (Taxonomy for Development in East Africa).

Contact

BioNET-EAFRINET Regional Coordinator: eafrinet@africaonline.co.ke