Grass

Long description

Sporobolus virginicus open tussock grassland to closed tussock grassland, with occasional emergent mangroves (usually Avicennia marina or Ceriops australis), Melaleuca spp., Acacia spp. and Clerodendrum inerme. Can also include Paspalum vaginatum, Fimbristylis ferruginea, Cyperus victoriensis and Cyperus scariosus, together with Eleocharis spiralis, Mnesithea rottboellioides, Marsilea mutica, Vincetoxicum carnosum, Ischaemum australe, Cyperus polystachyos, Ceratopteris thalictroides, Diplachne fusca, Suaeda australis, Suaeda arbusculoides, Sarcocornia quinqueflora subsp. quinqueflora and Tecticornia australasica[2].

Occurs on supratidal flats adjacent to mangroves and saltpans but on slightly more elevated substrate. Often only inundated by highest spring tides and dissected by small tidal channels. Typically forms a narrow belt between mangroves and alluvial communities, but can be extensive where there are large areas of low-lying sediments[2]. Often the most landward tidally influenced habitat (i.e. upper boundary of tidal influence) and the presence of S. virginicus can be a good indicator of tidal inundation and used to delineate upper tidal limit.

A variant of this ecosystem type that includes Aegicaras mangroves may be present in riverine channels - see Distribution.

Special values

Sporobolus virginicus grasslands may accumulate land through self-made detritus that builds up to elevate the level of the substrate. Stabilises intertidal area and creek banks and can trap terrestrial run-off/sediment.

Can provide habitat for the water mouse (Xeromys myoides). This species has been recorded in coastal saltmarsh ecosystems including saline grasslands, together with saline sedgelands, succulent shrublands, mangroves and freshwater wetlands.

Vegetated saltpan areas are generally inundated by the tide less frequently than mangroves, and these systems are under threat from sea level rise along seaward margins[2].

Sporobolus grasslands provide important fisheries habitat.

Diagnostic attributes

Inundation ‘Intertidal – Lower low’, ‘Intertidal – Mid low’, ‘Intertidal – Upper low’, ‘Intertidal – Low undifferentiated’, ‘Intertidal – Lower medium’, ‘Intertidal – Upper-medium’, ‘Intertidal – Medium undifferentiated’, ‘Intertidal – High’, ‘Intertidal – Undifferentiated’, ‘Intertidal – High undifferentiated’ although they occur closer to the higher tidal planes which remain unmapped

Structural macrobiota 'Grass'

Qualifiers

The Naturalness qualifier is relevant as tidal inundation may sometimes be modified by barriers, and excavated channels, modifying Inundation and Terrain morphology. Changes in tidal inundation will be reflected by changes in Structural macrobiota.

These ecosystems may fluctuate in extent over time and the relevant qualifiers are Period and Trend. Changing tidal inundation due to sea level rise is causing mangroves to colonise the saltmarsh ecosystems (list their numbers)[1].

Distribution

Saline grasslands occur throughout Queensland towards Highest Astronomical Tide, in association with sedgelands and saltpan.

The following relates to distribution of this ecosystem type within the Central Queensland mapping area:

• In Central Queensland these ecosystems are more common in the southern parts of mapping area, particularly in association with Baffle Creek and the Susan River. Unmapped areas occur within terrestrial Bioregion 12. On frontal dunes and beaches in Bioregion 12, can include Spinifex sericeus grassland and Casuarina equisetifolia subsp. incana low woodland/open forest with Acacia leiocalyx, Acacia disparrima subsp. disparrima, Banksia integrifolia subsp. integrifolia, Pandanus tectorius, Corymbia tessellaris, Cupaniopsis anacardioides and Acronychia imperforata.
• In Bioregion 12, all saltmarsh ecosystems are Environment Protect and Biodiversity Conservation Act 1999-listed (EPBC-listed) (i.e. grass-herb-sedge (1) and other saltmarsh ecosystem types (2, 3, 4 and 17) Curtis Island southward).
• In North Queensland (e.g. Ross River), ‘Transitional Wetlands’ are at the same tidal level as saltpans but are substantially different because they feature lush Sporobolus meadows instead of really high salt tolerant species found in saltpans. They also tend to feature Aegiceras mangroves rather than Ceriops. These transitional wetlands may occur in the channels of rivers where there is reasonably regular freshwater (this may stop the salinity reaching extreme levels). At the end of one of the driest years on record (2018), the Sporobolus in Annandale Wetland appeared to be stressed, whereas, following extensive flooding it appeared to be lush (potentially flushing salt out of the soil). Given its location, and its dependency on regular river flows, this variation in this ecosystem type is probably (a) of limited extent, and (b) at risk (M. Sheaves pers. comm.).

Comments

Other relevant attributes include Consolidation, Energy and Sediment texture as saline grasses typically grow on unconsolidated muds and fine sediments in low energy environments.

Additional Information

• Tidal planes - Maritime Safety Queensland
• Field Guide to common saltmarsh plants of Queensland

References

1. ^ Lovelock, C & Ellison, J (2007), Vulnerability of mangroves and tidal wetlands of the Great Barrier Reef to climate change.
2. ^ a b c Queensland Herbarium & Environmental Protection Agency, B (2005), Regional Ecosystem Description Database (REDD). Version 5.0. [online], Environmental Protection Agency, Brisbane. Available at: https://apps.des.qld.gov.au/regional-ecosystems/.

Last updated: 12 July 2019