wetlands in Western Australia
Wetland vegetation and flora, part 4:
In Chapter 2: Understanding wetlands
A guide to managing and restoring wetlands in Western Australia
Part 1: Overview – separate PDF
Includes glossary, references and appendices
Part 2: Kimberley – separate PDF
Part 3: Deserts – separate PDF
Part 4: Southwest – this PDF
Saline wetlands of the Southwest
Saline basin wetlands
Freshwater wetlands of the Southwest
Part 5: Southern Swan Coastal Plain – separate PDF
Profile of a wetland complex: Yalgorup National Park wetlands (Part 5)
Profile of a wetland complex: Brixton Street Wetlands (Part 5)
Western Australia is a very large state and there is a great deal of variability in wetland
vegetation and flora across it. The Southwest is one of three major climatic and
biogeographical zones (Figure 86):
• Kimberley – tropical, warm to hot all year, summer rainfall and a dry winter
• Deserts – hot desert, infrequent erratic rainfall
• Southwest – Mediterranean, warm to hot dry summer, cool wet winter.
The differing climate of these three regions drives important variations in wetland
Figure 86. WA’s bioregions and the three climatic zones used in this topic. Image – C. Auricht,
The next major driver of the wetland vegetation and flora characteristics of the
Southwest is whether they inhabit freshwater or saline wetlands. Wetland plant
communities are distinctive of the zone and water chemistry, contributing both to the
local and state identity and contributing greatly to the uniqueness of WA and Australia.
Thirdly, in addition to zone and freshwater/saline divisions, the Southwest wetlands
can be grouped according to the similarity of their vegetation characteristics. In the
Southwest zone, these groups are:
• saline lagoons
• saline basin wetlands
• saline riverine
• groundwater fed
• perched wetlands.
The Southwest is world renowned for its plant diversity and large number of endemic
plant species and communities. This diversity, combined with it being the wettest area
of the state, has resulted in an immense variety of wetlands. Also, being in the most
populous area of the state, these wetlands have suffered the greatest impacts from
clearing, agriculture and urban uses, leading to loss, fragmentation and degradation.
The Southwest wetlands are the best known and most studied in WA. A substantive
number of reports deal with a variety of plant-related wetland topics including:
descriptions of individual wetlands, groups of wetlands and regional groups, wetland
mapping; regional floristic data; and wetland management (related to various aspects
such as regions, reserves, rare species and communities). However, there are no true
regional overviews, databases or bibliographies on the Southwest’s wetland plants.
For the purposes of this topic, the Southwest incorporates nine bioregions: Yalgoo,
Geraldton Sandplains, Avon Wheatbelt, Swan Coastal Plain, Jarrah Forest, Warren,
Esperance Plains, Mallee and Coolgardie. The Yalgoo and Coolgardie are generally
considered to form an inter-zone between the Desert and the Southwest but, for
wetland vegetation and flora, are more closely related to that of the dry Southwest.
While the nine bioregions share some wetland characteristics, the overall variety of
wetland vegetation and flora is great.
There are fifty-eight listed nationally important wetlands in the Southwest, the most for
any of the three wetland zones.
Wetland vegetation of the Southwest
Broadly, the vegetation of the Southwest consists of Eucalyptus-dominated tall forest and
woodlands, Melaleuca-dominated forest and woodlands; Acacia woodlands, shrublands
and heath, Casuarina and Banksia low woodland; mallee woodlands and shrublands,
chenopod and samphire succulent shrublands and heath. As with the Kimberley and
Deserts, many of these vegetation types are present in wetlands but chenopod and
samphire succulent shrublands are confined to wetlands; further, some vegetation types
that are common in wetlands are rare at the broader level, including sedgelands and
herblands. There are so many wetland species in the Southwest that the most common
taxa cannot be listed here.
From the literature reviewed during the development of this topic, in excess of several
thousand different plant communities are potentially associated with the Southwest’s
wetlands, depending on the scale and detail of mapping. The wetland vegetation is
grouped below after a series of key features of the wetland habitats.
Many wetlands combine freshwater and saline wetland features in wetland complexes.
Two examples are provided at the end of this topic: the Yalgorup National Park wetlands
and Brixton Street wetlands complexes.
Saline wetlands are found in both coastal and inland locations throughout the region
and are described below in four principal groups: lagoons, saline basin wetlands, riverine
(including rejuvenated drainage and palaeo-drainage channels) and springs. The four
principal groups are subdivided further.
A feature of many of these saline wetlands is freshwater areas fed by seepages/springs
of fresh groundwater. These are described in this section on saline wetlands as they
are a significant component of these wetlands and are becoming increasingly rare as
groundwater levels generally decline in the Southwest. Most seepage areas associated
with salt lakes are of freshwater, forming unique communities and providing a water
supply for fauna.
but have recently (in geological timeframes) been isolated from the estuary or ocean. A
few retain seasonal linkages to the estuary or ocean and the boundaries with the saline
estuarine areas are poorly defined. Brearley
describes the estuarine systems. A number
bioregions are used to illustrate the vegetation of each type.
Only three of these are known and they are all included below.
• Abrolhos Islands (Geraldton Sandplains) – These lagoons are fringed by white
mangroves (Avicennia marina) and remain connected to the surrounding ocean.
• Rottnest Island* (Swan Coastal Plain) (Figure 87) – Located on Perth’s doorstep these
are the best documented and well known of the lagoon wetlands. The island’s lakes
are a unique wetland complex of eighteen salt lakes, sumplands and damplands,
covering more than 180 hectares. Seven are permanently inundated (lakes). The
three deepest lakes, Government House, Herschell and Serpentine lakes, are unique
having cool, low-salinity water overlying warmer higher saline water
and Sarcocornia quinqueflora with Gahnia trifida typically fringe the water. Patches
of Melaleuca lanceolata occur on the slight rises over the shrubs and sedges. The
aquatic Ruppia tuberosa found in these lakes is one of only two occurrences outside
Shark Bay. Cropped grasslands dominated by native couch (Sporobolus virginicus)
grow at the freshwater seepages found dotted around some of these lakes. These
communities are maintained by quokka grazing and are true marsupial lawns.
Interestingly, this complex contained some freshwater wetlands, rainfall being
perched on a marl layer. Unfortunately, these wetlands were mined for their marl, for
use in road works. Attempts are currently being made to reform these wetlands.
• Recherche Archipelago Islands (Esperance Plains) – Middle Island in the Recherche
Archipelago contains Lake Hillier, a saline lake usually coloured pink with the alga
Coastal Lakes (see below).
material (usually from dead
charophyte algae that are able
to biogenically precipitate
shrublands. Photo – B Keighery/OEPA.
• Hutt Lagoon* (Geraldton Sandplains) – Hutt Lagoon (Figure 88 and Figure 89) is a
brackish to saline wetland covering around 3,000 hectares, and fed by rain, surface
inflows and groundwater seepage. The wetland contains a complex series of fresh
to saline wetlands, with more than twenty distinct wetland plant communities.
occur on the eastern side of these wetlands and support sedgelands of Juncus
• Leeman Lagoons (Geraldton Sandplains) – Around Leeman there are a series of
permanently and seasonally inundated saline and gypsum wetlands with low rises
covered by Casuarina obesa woodlands over Gahnia trifida sedgelands
is dominated by Juncus kraussii subsp. australiensis, Cyperus laevigatus and Typha
Coolimba (Geraldton Sandplains).
• Lake Thetis* (near Cervantes, Swan Coastal Plain) – Water in this lake is saline to
hypersaline, with only the aquatic Ruppia tuberosa on the lake bed. Edges have
succulent shrublands of Sarcocornia quinqueflora, Tecticornia halocnemoides or
sedgelands of Gahnia trifida and Baumea juncea, all over herbs. The stromatolite
community of Lake Thetis is a TEC.
• Lakes Walyungup and Cooloongup (Swan Coastal Plain) – Like most lakes in the
Southwest, these periodically dry out and have also been called White Lakes in
reference to the dazzling white salt beds exposed on drying (Figure 90). Low
woodlands of Melaleuca cuticularis over sedgelands dominated by Gahnia trifida
and/or Juncus kraussii subsp. australiensis and samphire shrublands are associated
with these wetlands. Freshwater seepage areas on the margins of both lakes are
associated with low or tall forests dominated by Melaleuca rhaphiophylla and/or tuart
(Eucalyptus gomphocephala) over sedgelands dominated by Lepidosperma gladiatum,
Gahnia trifida and Baumea juncea. Some of these wetland communities are the TEC
‘Shrublands on calcareous silts of the Swan Coastal Plain’ (Figure 11).
• Yalgorup Lakes* (Swan Coastal Plain) – The waters of these lakes are seasonally
hyposaline (winter) or permanently hypersaline (for more information on the Yalgorup
Lakes complex, see ‘Profile of a wetland complex: Yalgorup National Park wetlands’,
located near the end of this topic).
(a) Eastern margin dominated by Gahnia trifida sedgelands.
(b) and (c) Habit and flowers of the native Cyperus laevigatus, a cosmopolitan sedge of the
areas with fresher water.
(a) Looking west towards the coastal holocene dunes across a saline flat with patches of Juncus
(b) Flowers of Samolus repens var. paucifolius, a plant scattered through these communities.
(c) This is a plant of the coastal saline wetlands between Shark Bay and the Yalgorup
Wetlands. Mapping – P Gioia. Image used with the permission of the Western Australian
Herbarium, DEC. Accessed 21/06/2011.
Figure 90. Lake Walyungup, a salt lake near Rockingham (Swan Coastal Plain).
(a) The salt encrusted dry lakebed is surrounded by bands of Juncus kraussii subsp. australiensis
sedgelands and samphire shrublands. Wetlands with fresher water around the outside margins
are dominated by Lepidosperma gladiatum. Acacia shrublands are found on the dry rises.
Photo – B Keighery/OEPA.
(b) Lake Walyungup lies to the west of a band of Quindalup Dunes, with Spearwood Dunes
to the east (transect diagram reproduced and adapted from Department of Minerals and
Culham Inlet Lagoons* (Esperance Sandplains) – These wetlands are estuarine areas
where the sand bar is rarely breached; they are, therefore, no longer truly estuarine
and are fed by naturally saline rivers. For example, Culham Inlet, fed by the Phillips and
Steere rivers, had not breached to the sea for at least 150 years before recent clearing for
agriculture in the catchment. Similar systems include the Fitzgerald and Dempster inlets.
These have the same vegetation as the Esperance Coastal Lakes.
Saline basin wetlands
These extend from near Frankland and Albany to east of Esperance (Figure 91). An
example is Kwornicup Lake (Jarrah Forest), with a mosaic of vegetation units including:
a Wilsonia backhousei herbland (on the lake bed); Tecticornia syncarpa and Sarcocornia
or Eucalyptus rudis. To the east, north of the Stirling Ranges, is the Balicup System (1,400
hectares) containing Camel, Balicup, Jebarjup and Swan lakes (Esperance Sandplains).
The Balicup System is typical of naturally saline lakes around the range.
unusual species are found in the samphire shrublands, including Tecticornia uniflora.
A further example of this type is the Jerdacuttup Lakes (east of Hopetoun, Esperance
Sandplains) with Tecticornia indica samphire shrubland and a Melaleuca cuticularis forest
Figure 91. Salt lake in Truslove Nature Reserve (Esperance Sandplain). Photos – B Keighery/
bare drying lake bed.
(b) Samphire shrubs and the prostrate succulent Disphyma crassifolium subsp. clavellatum.
This complex includes the Lake Gore System*, Lake Warden System*, Mortijinup Lake
System* and Pink Lake*. All are fringed by Melaleuca cuticularis woodlands often over
a sedgeland dominated by Juncus kraussii subsp. australiensis, Gahnia trifida, Baumea
Where groundwater is naturally saline, as in the northern Perth Basin, the lakes are
saline. An example is Lake Eganu (north of Moora) which is bare in the middle then
edged with zoned vegetation from Tecticornia pergranulata samphire shrubland to
Cataby) has bands of vegetation relating to inundation and salinity.
The lake is bare
and Lawrencia glomerata shrubland, a Tecticornia indica and T. pergranulata samphire
shrubland with herbs and grasses and finally a fringing shrubland of Melaleuca viminea.
Patches of saline wetland are found within a number of predominantly freshwater
wetlands. When these saline wetlands are on clays they support a suite of annual herbs
and sedges (Figure 92). These same herbs and sedges are also found in some of the
Figure 92. Some annual species renewed from seed found in the herblands of saline clayflats.
Photos – B Keighery/OEPA.
(a) The sedge Centrolepis polygyna.
(b) Two daisies, the newly described Blennospora doliiformis (left) and Pogonolepis stricta.
(c) Angianthus drummondii, one of the wetland species recently separated from the species
Much of southern WA is composed of a low relief lateritised plateau with active
drainage. In the higher rainfall areas (including the Jarrah Forest and Avon Wheatbelt)
the rejuvenated drainage lines still connect to the sea and flow most years. Further
inland, as rainfall decreases, flows decline and occur only in wet periods, forming braided
saline drainage systems. Extensive braided drainage systems are found on all of the major
rivers. These often have high vegetation and flora values, especially those of the Mortlock
River and the Yenyening System on the Avon River (Avon Wheatbelt). Work on mapping
the vegetation of the Yenyening System
has distinguished twenty-two vegetation
include: saline wetlands with three types of samphire shrublands, Casuarina obesa forest
over Juncus kraussii subsp. australiensis sedgeland, Hopkinsia anaectocolea sedgeland,
herblands, Eucalyptus sargentii woodland over chenopod shrubland, Eucalyptus
mixes of Melaleuca hamata, M. brophyi, M. halmaturorum and M. lateriflora. Scattered
through the area are perched, mostly freshwater, wetlands that support Callistemon
phoeniceus and Melaleuca thyoides shrubland and M. brevifolia shrubland over Baumea
riparia and Juncus kraussii subsp. australiensis sedgelands. Eight species of uncommon
flora (priority flora) are located in the wetlands, including the only known populations of
a new Arthropodium species. All of the braided systems are threatened by hydrological