Marsh Club-rush sedgeland in the Darling Riverine Plains Bioregion - critically endangered ecological community listing

The Scientific Committee, established by the Threatened Species Conservation Act, has made a Final Determination to list the Marsh Club-rush sedgeland in the Darling Riverine Plains Bioregion, as a CRITICALLY ENDANGERED ECOLOGICAL COMMUNITY in Part 2 of Schedule 1A of the Act. Listing of Critically Endangered Ecological Communities is provided for by Part 2 of the Act.

NSW Scientific Committee - final determination

The Scientific Committee has found that:

1. Marsh Club-rush sedgeland in the Darling Riverine Plains Bioregion is the name given to the ecological community characterised by the species assemblage listed in paragraph 2. The community typically forms dense stands to 2 m high in which trees are absent but structural characteristics of the community may vary, depending on the intensity and characteristics of past disturbances including grazing, fire and alteration of flow regimes.

2. Marsh Club-rush sedgeland in the Darling Riverine Plains Bioregion is characterised by the following assemblage of species:

• Bolboschoenus fluviatilis
• Carex appressa
• Eleocharis plana
• Lachnagrostis filiformis
• Paspalum distichum
• Ranunculus undosus

3. The total species list of the community is larger than that given above, with some species present in only one or two sites or in low abundance. The species composition of a site will be influenced by the size of the site, recent rainfall or drought condition and by its disturbance history. The number of species, and the above ground relative abundance of species will change with time since flooding, and may also change in response to changes in flow regime (including changes in flooding frequency, depth and duration). At any one time, above ground individuals of some species may be absent, but the species may be represented below ground in the soil seed banks or as dormant structures such as bulbs, corms, rhizomes, rootstocks or lignotubers. The list of species given above is of vascular plant species; the community also includes micro-organisms, fungi, cryptogamic plants and a diverse fauna, both vertebrate and invertebrate. These components of the community are poorly documented.

4. Marsh Club-rush sedgeland is dominated by the Marsh Club-rush Bolboschoenus fluviatilis which forms dense stands up to 2 m tall with an understorey including  Carex  appressa (Tussock Sedge),  Eleocharis plana (Ribbed Spike Rush),  Lachnagrostis filiformis (Blown Grass),  Paspalum distichum (Water Couch) and  Ranunculus undosus (Swamp Buttercup) (Bowen  et al. 2008). The ecological community is distinguished from other surrounding ecological communities by a combination of lack of trees and dominance of  Bolboschoenus fluviatilis (Marsh Club-rush), generally over 40% of the vegetation cover is dominated by this species. Surrounding communities may include  Eucalyptus coolibah (Coolibah) and  E. largiflorens (Blackbox) woodlands, shrublands of  Acacia stenophylla (River Coobah) and  Muehlenbeckia florulenta (Lignum) or treeless communities dominated by  Paspalum distichum (Water Couch),  Eleocharis plana (Spike Rush),  Juncus aridicola (Tussock Rush) or  Phragmites australis (Common reed).  Bolboschoenus fluviatilis is widespread in NSW and may occur as a component species in these surrounding communities and in a range of other wetland locations.

5. Marsh Club-rush sedgeland is associated with grey clay soils usually with a surface layer of organic matter several centimetres thick. The community has been described by Benson (2008) as ID 205 Marsh Club-rush very tall sedgeland of inland watercourses.

6. Marsh Club-rush sedgeland has been recorded in the Gwydir wetlands but may occur elsewhere in the Darling Riverine Plains Bioregion.

7. Marsh Club-rush sedgeland has a very highly restricted geographic distribution and an estimated area of occupancy of 8 km² based on 2 x 2 km grid cells, the scale of assessment recommended for species by IUCN (2008).

8. Floodplain wetland communities have undergone significant changes to their hydrological regimes as a result of river regulation (Kingsford 2000). The construction of large dams to utilise unpredictable river flows and facilitate the expansion of irrigated agriculture has altered the frequency, size and duration of floods, often reducing the connectivity between rivers and their floodplains (Boulton & Brock 1999). Within the Gwydir wetlands the cycles of floodplain wetting and drying have a major influence on the productivity of Marsh Club-rush sedgeland and the maintenance of flow regimes into these wetlands is essential for sustaining vegetation condition (Wilson et al. 2008). However, since regulation of flows to the Gwydir Wetlands began in 1972 and the development of Copeton Dam in 1976, there has been a decrease in available flows to the wetlands (Bowen & Simpson 2009; B Southern  in litt 2010). A large proportion of the water that historically reached the wetlands of the Lower Gwydir Watercourse is now diverted for various purposes, such as irrigation and stock and domestic use. Bowen and Simpson (2009) note that the Lower Gwydir Wetlands have only received managed environmental releases and waters from a few larger floods in 1984, 1996, 1998, 2000, 2001 and 2004. ‘Alteration to the natural flow regimes of rivers and streams and their floodplains and wetlands’ is listed as a Key Threatening Process under the  Threatened Species Conservation Act 1995.

9. Analysis of the distribution of the Marsh Club-rush sedgeland community in the Gwydir wetlands by Bowen et al. (2008) showed a decrease in geographic distribution from 317 ha in 1996 to 132 ha in 2005. Bowen and Simpson (2009) estimated an area of occupancy of 181 ha in 2008 which represents only 9% of the 1974 extent of the Marsh Club-rush sedgeland community. This indicates a very large reduction in the community’s geographic distribution over the past 35 years, a time span appropriate to the life cycle and habitat characteristics of this community’s component species. This magnitude of decline is consistent with local observations since the 1950’s (B Southern  in litt. 2010).

10. Grazing by livestock and changes to patterns of wetland inundation may accelerate the invasion of weeds into Marsh Club-rush sedgeland. Comparisons of grazed and ungrazed exclosure plots in the Gwydir wetlands showed lower cover of Bolboschoenus fluviatilis and increased abundance of  Cirsium vulgare (Thistle) at grazed sites, indicating a significant change in both community structure and composition (Wilson  et al. 2008). Similarly, Taylor and Ganf (2005) have highlighted the likely correlation between reduced grass canopy cover via grazing and proliferation of the floodplain weed,  Phyla canescens (Lippia), in the northern Murray-Darling Basin. Particularly within the Gwydir wetlands, Bowen  et al. (2008) have noted that Lippia invasion is one of the most important factors contributing to the overall loss of wetland vegetation.

11. Marsh Club-rush sedgeland in the Darling Riverine Plains Bioregion is eligible to be listed as a Critically Endangered Ecological Community as, in the opinion of the Scientific Committee, it is facing an extremely high risk of extinction in New South Wales in the immediate future, as determined in accordance with the following criteria as prescribed by the Threatened Species Conservation Regulation 2002:

Clause 25

The ecological community has undergone, is observed, estimated, inferred or reasonably suspected to have undergone or is likely to undergo within a time span appropriate to the life cycle and habitat characteristics of its component species:

(a) a very large reduction in geographic distribution.

Clause 26

The ecological community’s geographic distribution is estimated or inferred to be:

(a) very highly restricted,

and the nature of its distribution makes it likely that the action of a threatening process could cause it to decline or degrade in extent or ecological function over a time span appropriate to the life cycle and habitat characteristics of the ecological community’s component species.

Clause 27

The ecological community has undergone, is observed, estimated, inferred or reasonably suspected to have undergone or is likely to undergo within a time span appropriate to the life cycle and habitat characteristics of its component species:

(a) a very large reduction in ecological function,

as indicated by any of the following:

(d) change in community structure,

(e) change in species composition,

(f) disruption of ecological processes,

(g) invasion and establishment of exotic species,

(h) degradation of habitat,

(i) fragmentation of habitat.

Dr Richard Major
Chairperson
Scientific Committee

Proposed Gazettal Date: 24/09/10

Exhibition Period: 24/09/10 – 19/11/10

References:

Benson JS (2008) New South Wales Vegetation Classification and Assessment: Part 2 Plant communities in the NSW South-western Slopes Bioregion and update of NSW Western Plains plant communities. Version 2 of the NSWVCA database. Cunninghamia10,  599-673.

Boulton AJ, Brock MA (1999) ‘Australian freshwater ecology: processes and management.’ (Gleneagles Publishing: Adelaide)

Bowen S, Simpson SL (2009) ‘Changes in extent and condition of the vegetation communities of the Gwydir Wetlands and Floodplain 1996-2008 Final Report for the NSW Wetland Recovery Program’. NSW Department of Environment Climate Change and Water, Sydney.

Bowen S, Simpson S, McCosker R (2008) ‘Changes in extent and condition of floodplain wetland vegetation communities in the Gwydir wetlands and floodplain 1996-2005’. New South Wales Department of Environment and Climate Change, Sydney.

IUCN (2008) ‘Guidelines for using the IUCN Red List Categories and Criteria. Version 7.0.&rsrsquo; (Standards and Petitions Working Group of the IUCN Species Survival Commission Biodiversity Assessments Sub-committee: Switzerland).

Kingsford RT (2000) Ecological impacts of dams, water diversions and river management on floodplain wetlands in Australia. Austral Ecology25,  109–127.

Taylor B, Ganf GG (2005) Comparative ecology of two co-occurring plants: the native Sporobolus mitchellii and the exotic  Phyla canescens.  Marine and Freshwater  Research56,  431-440.

Wilson GG, Berney PB, Ryder DS, Price JN (2008) ‘Stage 2: Grazing/Landuse in the Macquarie Marshes and Gwydir Wetlands.’ Final report to the New South Wales Department of Environment and Climate Change, University of New England, Armidale.