Marram Grass (Ammophila arenaria)

Photo: (c) Kenraiz Krzysztof Ziarnek CC BY-SA 4.0 license

Family:  Poaceae

Growth Habit: Marram Grass develops deep and extensive rhizomes (roots)  and produces dense clumps of grass, often up to a metre or so high, which dominate plant communities and entrap sand. It is more vigorous where sands are mobile, covering the plant and stimulating growth. It is readily distinguished from the native species that bind dunes. Marram grass has long, silvery leaves up to 60 cm long and soft, silvery, long cylindrical inflorescences, where as Austrostipa has sharp pointed leaves and Spinifex has spherical inflorescences.

Type of Plant: Tall dense perennial grass

Photo: (c) Matt Lavin CC BY-SA 2.0 license

Flowers: Long cylindrical inflorescences. The spike-like inflorescences are borne at the tips of the stems, 7-30 cm long and 1-3 cm wide, consist of several branches that are held closely to the stem and contain numerous densely arranged flower spikelets (10-18 mm long). The individual flower spikelets are elongated in shape (i.e. narrowly-oblong) and borne on stalks 1-4 mm long. They consist of a pair of bracts and a single tiny floret. The floret has two floral bracts (i.e. a lemma and palea), three stamens (4-7 mm long) and an ovary topped with a feathery two-branched stigma. Flowering occurs mainly from October to February.

Fruits/Seeds: Seeds are often sterile. The seed-heads turn from green to straw-coloured or pale brown as they mature. The flower spikelets break apart at maturity, with the bracts (i.e. glumes) remaining on the seed-head and the floret being dispersed. The ‘seeds’ (i.e. grains or caryopses), when present, are egg-shaped (i.e. obovoid).

Dispersal: The main methods of spread are either the extension of rhizomes under ground over very large distances or by sea currents washing fragments of the rhizomes around the coast where they wash  ashore and establish communities.

Distribution: Generally Marram Grass is found on northern and eastern Tasmanian beaches.  Many of these beaches are now dominated by marram grass and many others have small infestations. However there are records of Marram Grass right around the coastline of Tasmania and offshore islands.

Status: Not declared in Tasmania but is a significant environmental weed.

Weed Impacts:

  • Able to spread rapidly and over long distances from dune stabilisation projects to invade other coastal areas.
  • Coastal processes are radically and permanently altered.
  • Marram Grass produce coastal landforms which have completely different shapes to dunes produced by native plants. Large steep faced, highly erodible dunes are characteristic of areas with Marram Grass, leading to coastal recession.
  • The build up of dunes by Marram Grass removes sand from the beach, surf and near shore zone and so has serious consequences for the natural dynamics of the coastal environment.
  •  Outcompetes native vegetation, especially grasses.
  • Displaces native coastal vegetation communities.
  • Loss of beach nesting sites for shorebirds such as the threatened Hooded Plover.

Control Methods:

  • Extremely difficult to control.
  • Reduce disturbance as much as possible, including burning. Where it occurs on sands that are not disturbed, native species such as coastal wattle (Acacia sophorae) can establish if there is a seed source and gradually out shade the marram grass leading to a succession to a native community.
  • Do not use Marram Grass in dune stabilisation projects.
  • Protect areas with no, or limited infestations. Monitor beaches that are free of the grass for infestations.
  • Control Marram Grass around threatened species and communities and important Aboriginal sites.
  • Seek advice from the Parks & Wildlife Service as there could be adverse impacts e.g. sand destabilisation, erosion of heritage sites.

N.B. Always check the herbicide label before use.