Taxon Attribute Profiles

Juncus ingens on Gulpa Creek near Mathoura (© Sainty and Jacobs, 1981)

Juncus ingens N.A.Wakef.

Giant Rush

Introduction

Juncus ingens is a large native rush found predominately along the Murray River in New South Wales and Victoria. Growing in waterlogged soil or shallow water and relying on frequent flooding for its long-term survival, Juncus ingens provides an important bird nesting habitat in some wetlands.

Taxonomy and Ecology

Classification

Family: Juncaceae
Genus: Juncus – c. 300 species worldwide with 31 species endemic to Australia and a further 21 species naturalised (Wilson et al., 1993).

Life form

click to enlarge map

Juncus ingens is a very tall rush approximately 1.5 m to 5 m high. Its cylindrical culms range from 4 mm to 10 mm in diameter and rise from a strongly rhizomatous base. It is apparently the largest rush in the world (Cunningham et al., 1981) and is the only species in the Juncaceae to form extensive mono-specific stands (Roberts and Marston, 2000). See Albrecht (1994) and Wilson et al. (1993) for further descriptive information.

Distribution

Juncus ingens is found in New South Wales and Victoria, predominantly along the Murray River from near Albury to Barham, east of Swan Hill, and further south and west into Victoria (Albrecht, 1994; Wilson et al., 1993).

Habitat

Juncus ingens is found in shallow water (Cunningham et al., 1981). It is usually found on heavy soils within and on the margins of lakes, billabongs, other semi-permanent waterbodies and drainage channels (Albrecht, 1994; Wilson et al., 1993).

"Status" in community

Juncus ingens often forms monospecific stands (Roberts and Marston, 2000). In the Barmah area of Victoria Juncus ingens dominates some of the areas which are treeless due to late flood recession preventing forest establishment (Chesterfield, 1986).

Associated species

Juncus ingens grows in permanent shallow water and periodically flooded areas on lagoon and swamp communities in Eucalyptus camaldulensis (river red gum) communities (Cunningham et al., 1981) and floodplain, wetland and marsh communities (Department of Sustainability and Environment, 2004). Due to Juncus ingens frequently growing in monospecific stands there are relatively few associated species recorded. In the Barmah red gum forest area of Victoria water milfoil (Myriophyllum propinquum), clovestrip (Ludwigia peploides), azolla (Azolla filiculoides) and water pepper (Persicaria hydropiper) can occur in the intertussock spaces, although there is usually just mud or water (Chesterfield, 1986). Other herbs such as Isolepis inundata, Cotula coronopifolia, Senecio glomeratus have been recorded growing on drying mud amongst stands of Juncus ingens along with Phragmites australis in swamps (Australian National Herbarium, Canberra, 2005).

Qualitative and quantitative data – abundance, cover, biomass

Juncus ingens is very common within its range. It usually forms extensive, pure stands and can form almost impenetrable thickets (Albrecht, 1994; Cunningham et al., 1981)

Species – interactions with other biodiversity

Juncus ingens is known to be a nesting site for ibis in some wetlands (e.g. the Wanganella swamps, southern Riverina) (Roberts and Marston, 2000; Murray Darling Basin Commission, 2004). However, the increase in Juncus ingens relative to the Common Reed (Phragmites australis) and Cumbungi (Typha orientalis), due to altered flooding regimes, may have led to the decrease in numbers or disappearance of some birds such as the Brolga (Grus rubicundus), Little Bittern (Ixobrychus minutus) and Spotless Crake (Porzana tabuensis) in the Barmah Forest (Chesterfield et al., 1984).
Chesterfield (1986) has suggested that the change in the water regime in the Barmah area as a result of river regulation on the Murray has allowed Juncus ingens to out compete the Moira grass (Pseudoraphis spinescens) previously found to a much greater extent.

Physiological traits and adaptations

The roots and rhizomes of many aquatic plants grow in anaerobic sediments. Some aquatic species increase gas to their roots and rhizomes by pressure convective flow of gases. This is an important adaptation to growth in anoxic conditions and is believed to confer an advantage over plants that rely on diffusive gas transport. While Juncus ingens pressurizes its culms it has very high resistance to flow at the culm-rhizome junction. This results in very low convective flows. This may contribute to the species being restricted to shallower waters (< 1 m deep) (Brix et al., 1992).

Reproduction and Establishment

Female (left) and male (right) inflorescences of Juncus ingens (© Sainty and Jacobs, 1981).

Juncus ingens inflorescences (female left and male right) and capsule (© Albrecht, 1994, Flora of Victoria Vol 2:208).

Reproduction

Juncus ingens is one of only two dioecious Juncus species known in Australia (Wilson et al., 1993).

In Victoria Juncus ingens generally flowers from October to January, shedding seed from December to April (Albrecht, 1994).

Dispersability; establishment and growth

Juncus ingens has the ability to rapidly colonise suitable areas (Chesterfield, 1986). Seedlings are thought to be intolerant of extended submersion. As a result, regeneration is unlikely in flooded areas (Chesterfield, 1986; Roberts and Marston, 2000). Although there is no empirical data available, expert opinion suggests that 60-80 days is the preferred interval between floods. Longer periods may lead to seedling death but shorter periods (1.5 months or less) can lead to insufficient growth (Murray Darling Basin Commission, 2004). Suitable germination conditions are wet mud in spring to summer after the recession of late winter and spring floods (Murray Darling Basin Commission, 2004).

Juvenile period

While no specific information relating to the juvenile period of Juncus ingens has been located at this time it is thought that seedlings are intolerant of extended submersion but will also die if the period between flood events is too long (see Dispersability: establishment and growth).

Hydrology and salinity

Hydrology

Juncus ingens is found in shallow or water-logged conditions. It does not grow in deep water (Roberts and Marston, 2000) but can tolerate depths of up to 1.5 m during flooding events in northern Victoria (Ward, 1996, in Roberts and Marston, 2000). While no experimental or field data is available it is thought that water levels need to be at least covering the plant roots but no deeper than two-thirds of the plant's height to allow for respiration (Murray Darling Basin Commission, 2004).

In the Barmah-Millewa Forest the rushlands are free-draining and therefore are only inundated when river levels are high. Under natural conditions, inundation occurred every year and lasted for 8.7 months on average. Dry periods lasting an average of 3.9 months would have occurred in 4 out of 5 years. Under the conditions current in 1989, flooding duration had significantly decreased with dry periods lasting for more than 10 months at a time (Leitch, 1989).

Salinity tolerance

No information regarding the salinity tolerance of Juncus ingens has been located at this time.

Flooding regimes

Juncus ingens is associated with frequent flooding (Bren and Gibbs, 1986; Chessman and Jones, 2001). Rushlands were associated with a higher frequency of floods, longer flood duration and shorter periods between flooding events than the Moira grasslands and surrounding red gum forest on the Murray River (Bren, 1992).

Current distribution of Juncus ingens in the Murray-Darling Basin suggests a mean flood duration of 4 months, with flooding occurring most years (Roberts and Marston, 2000).

While clumps of Juncus ingens can survive extended dry periods, extensive beds require regular and extended flooding (J. Frankenberg, pers. comm. in Leitch, 1989). Flooding in May to November is the preferred timing with the flood duration lasting between 4 to 9 months being optimal (Murray Darling Basin Commission, 2004).

Change in water regimes

Because Juncus ingens is dependent on regular watering for vigorous growth, its distribution may change in response to changes in water regimes (Chesterfield, 1986).

In the Barmah area, winter and spring floods would normally prevent Juncus ingens from colonising the low-lying Moira grass (Pseudoraphis spinescens) grasslands as the seedlings cannot survive complete submersion for extended periods. River regulation on the Murray reduced winter-spring flooding over a number of years allowing Juncus ingens to establish in areas previously occupied by Moira grass. River regulation has also resulted in the soils of some low lying areas remaining wet, particularly over summer, further assisting the expansion of the species (Chesterfield, 1986). In contrast, other areas of Juncus ingens have contracted. This is possibly due to the de-snagging of creeks to improve drainage (Chesterfield, 1986) and changes in the natural flooding regime resulting in a reduction of inundation of some rushland areas allowing river red gum to invade (Maunsell, 1992).

Response to disturbance (non-hydrological)

Grazing

Stock do not appear to graze on Juncus ingens (Cunningham et al., 1981). Neither the roots nor shoots are edible (Chesterfield, 1986).

Weeds

No specific information has been located at this time. However, Juncus ingens is a robust species and appears to be unaffected by weeds.

Conservation status

Juncus ingens is not considered to be at risk. It appears to have been favoured by hydrological changes in some areas, such as the Barmah-Millewa Forests, where it has become more widespread invading Moira grass grasslands (Chesterfield, 1984; Maunsell, 1992).

Uses (including ethnobotanical)

The species can be useful in bank stabilization (Sainty and Jacobs, 1981). A 1997 survey found that Juncus ingens was one of the most commonly cited dominant species for rehabilitation projects of inland marshes (Streever, 1997). CSIRO Land and Water are currently trialing a system to treat sewage effluent involving the planting of Juncus ingens over a traditional FILTER waste water treatment system. Drainage from the system can be used to water adjacent plants (Blackwell et al., 2005).

Summary

The largest rush in the world and the only member of the Juncaceae to form mono-specific stands, Juncus ingens is a highly visible component of the flora along the upper reaches of the Murray River. Juncus ingens is particularly sensitive to the timing and length of flooding events in its habitat for both reproduction and plant survival. Current regimes in the Murray Darling Basin have clearly altered its distribution. While in some areas this has resulted in a contraction of the population of the species, in other areas Juncus ingens populations have expanded, invading previously existing grasslands. It is currently not considered threatened. While it may be useful for bank stabilisation, its expansion at the expense of other wetland species due to favourable hydrological changes may result in the loss of biodiversity, particularly amongst wetland birds who rely on different wetland floral communities for breeding.

References

Albrecht, D.E. (1994) Juncus. In Walsh, N.G. and Entwisle, T.J. (eds) Flora of Victoria Vol. 2: Ferns and Allied Plants, Conifers and Monocotyledons. Inkata Press, Melbourne, p. 204.

Australian National Herbarium, Canberra. (2005) Australian National Herbarium Specimen Information Register. Available at: http://www.anbg.gov.au/cgi-bin/anhsir [Accessed: January 2005].

Blackwell, J., Jayawardane, N.S., Christen, E.W., Zandona, L., Zandona, R., Manente, R. and Carroll, J. (2005) Sustainable, Aesthetic, Environmentally Sensitive and Inexpensive On Site Sewage Management. Sustainable Irrigation System Directorate, CSIRO Land and Water. Presentation to the CSIRO Awards, 8 February 2005.

Bren, L.J. and Gibbs, N.L. (1986) Relationships between flood frequency, vegetation and topography in a river red gum forest. Australian Forest Research 16, 357-370.

Bren, L.J. (1992) Tree invasion of an intermittent wetland in relation to changes in the flooding frequency of the River Murray, Australia. Australian Journal of Ecology 17, 395-408.

Brix, H., Sorrell, B.K. and Orr, P.T. (1992) Internal pressurization and convective gas flow in some emergent freshwater macrophytes. Limnology and Oceanography , 37(7): 1420-1433.

Chessman, B. and Jones, H. (2001) Integrated monitoring of environmental flows: design report. New South Wales Department of Land and Water Conservation, Parramatta

Chesterfield, E.A., Loyn R.H. & Macfarlane M.A. (1984) Flora and fauna of Barmah State Forest and their management. Research Branch Report No. 240, Forests Commission Victoria, Melbourne. Quoted in Management Plan for Barmah State Forest

Chesterfield, E.A. (1986) Changes in the vegetation of the river red gum forest at Barmah, Victoria. Australian Forestry 49, 4-15.

Cunningham, G.M., Mulham, W.E., Milthorpe, P.E. and Leigh, J.H. (1981) Plants of Western New South Wales. Soil Conservation Service of New South Wales. p. 178.

Department of Sustainability and Environment (2004) Ecological Vegetation Classes (EVC) Benchmarks by Bioregion. Available at http://www.dse.vic.gov.au/dse/nrence.nsf [Accessed August 2005].

Leitch, C. (1989) Towards a Strategy for Managing the Flooding of Barmah Forest. Department of Conservation, Forests and Lands, Benalla, Victoria.

Maunsell Pty Ltd. (1992) Barmah-Millewa Forest Water Management Plan. Prepared for the Murray-Darling Basin Commission by Maunsell Pty Ltd, Bewsher Consulting, BHP Engineering, Land Technologies Division, Consulting Environmental Engineers, Dwyer Leslie and Ian Drummond and Associates. Murray Darling Basin Commission, Canberra. January 1992.

Murray Darling Basin Commission (2004) Murray Darling Basin Commission – the Murray Flow Assessment Tool. Giant rush rushland. Available at http://www.mdbc.gov.au/livingmurray/mfat/wetland/za_giantrush.htm [Accessed February 2005].

Murray Darling Basin Commission. (date unknown) Juncus (Giant) Rush. Available at http://www.mdbc.gov.au/education/encyclopedia/wildlife/flora/juncus_rush.htm [Accessed February 2005].

Roberts, J. and Marston, F. (2000) Water regime of wetland and floodplain plants in the Murray-Darling Basin. A sourcebook of ecological knowledge. CSIRO Land and Water, Canberra.

Sainty, G.R. and Jacobs, S.W.L. (1981) Waterplants of New South Wales. Water Resources Commission New South Wales, Sydney.

Streever, W.J. (1997) Trends in Australian Wetland Rehabilitation. Wetlands Ecology and Management 5: 5–18.

Wilson, K.L. Johnson, L.A.S. and Bankoff, P. (1993) Juncus . In G.J. Harden (ed) Flora of New South Wales. Vol. 4. University of NSW Press, Sydney, p. 284.