Riverina

The Riverina natural region as recognised by Conn (1993) comprises the Victorian Riverina and Murray Fans regions in the current system of bioregions in Victoria.

Location

RiverinaThis region is defined largely on topographicaland geological features, However, these featuresand the vegetation are strongly correlated. TheRiverina includes the eastern part of the MurrayBasin. The southern and eastern boundary ofthe region occurs at an elevation of about 150metres and adjoins the low hills and ranges ofthe Midlands (Victoria) and South-western Slopes(New South Wales). It extends north to a latitudeof about 33, including Ivanhoe and ConobleLake (in New South Wales). The western boun dary of this region is the boundary between theaeolian and fluviatile landforms, and associatedsoils and vegetation. The aeolian landform sup ports the malice communities of the Murray Mal ice Region.

Major grids G, H, L, M, Q and R.Approximate area 23 864 km2 .

Major landforms

The Riverina (`Riverine Plain' of Butler ct al.1973) includes the eastern part of the Cainozoicsedimentary Murray Basin. The Murray Basinresults from regional subsidence with upwarp ing of the marine sediments during the Quater nary (Hills 1939). The unconsolidated fluviatiledeposits beneath the current riverine plain arebetween 90 and about 305 metres thick (Butleret al. 1973).

The surface of the riverine plain shows evi dence of ancient stream channels (paleochan ncls) (Butler et al. 1973; Curney & Dole 1978;Macumber 1978). See Bowler (1967) and Pels(1969) for accounts of the prehistory of theregion. The modern drainage of the riverineplain forms a tributary system, with most tribu taries joining the Murray River before it leavesthe plain. Several major streams have smallerstreams branching from them. Some of thesesubsequently rejoin the main stream downstream(e.g. Edward River, New South Wales), whereasothers divert the flow from the main tributarysystem and terminate in lakes, salt pans or dune fields. Examples of channels that divert wateraway from the Murray River tributary systeminclude those associated with the Avoca andLoddon Rivers, Victoria (Hills 1940); and theLachlan River, New South Wales (Mitchell 1839).Shallow, dry lakes (playas) are distributedwidely in the region. They are very common inthe Avoca-Loddon Rivers area (Victoria) andto the west of the Lachlan River (New SouthWales). The dry basins vary according to thesalinity of their surfaces. Several saline basins(Salinas) occur near Kerang. There are very fewpermanent lakes with extensive expanses ofwater. Aeolian-derived landforms occur infre quently in the region. They occur either as lun ettes, that are associated with lakes, as sand dunesderived f rom the ' sandy deposits of ancientstreams, or as scalds (bare areas produced bythe removal of the surface soll~ ).

The Riverina consists of several very gentlysloping alluvial fans and the floodplains ontowhich the fans merge. These fans merge to forma single low-gradient fan between the Loddonand Lachlan Rivers.

The soil types of the region vary from grey,brown, to red clays (often of high salinity), andto red-brown earths. The soils of the floodplainareas are grey days and silty days, with lowsalinity. Red and yellow duplex soils are wide spread on the older, upper river terraces andfans. For further details refer to Butler (1950);Butler and Hubble (1978); Butler et al. (1973);Rowe, Crouch and van Dijk (1978); and Gib bons and Rowan, this volume.

Climate

The general climatic trend in the region is one ofgradation, characterized by increasingly longerand warmer summers from the south-east to thenorth-west (Anon. 1983). The average annualrainfall decreases from south-east to north west, The region has a winter maximum rainfall(250-500 mm per annum). The winds are pre dominantly from the north-west, west and south west. Frequent north-westerly winds bring withthem hot, dry air from central Australia duringthe summer months. Annual evaporation farexceeds the annual precipitation. Frosts arecommon and may be severe, and the region is drought-prone (see also _Climate of Vict.oria',this volume).

Vegetation

Prior to European settlement the natural veg etation consisted of woodlands dominated byEucalyptu~ and Callit. Most of the latter com munities have been cleared for agriculture.A summary of the vegetation of this region isbased on small scattered remnants and thatwhich occurs on public land (such as State For ests). Insufficient vegetation remains to enableeach alliance to he fully circumscribed.

Forests and woodlands

Eucalyptus camaldulensis (River Red-gum)

Eucalyptus camaldulensis occurs as a dominant ofopen-forest or woodland (28-40 metres high),particularly in areas that receive regular flood ing (Dexter 1978). It occurs as a narrow bandalong the tops of river banks or as woodlands(less frequently as forests) in flooded areas. Inthis region much of this community occurs onheavy clay soils. E. camaldulens usually formspure stands, but occasionally it forms ecotonalassociations with other watercourse species or with other species that are typical of the neigh bouring woodlands (e.g. E. me/Izo~ dora and E.microcarpa). The understorey is usually sparse,with woody shrubs being localized aroundwatercourses and on sandy ridges within thefloodplain forest. An understorey of small treesand saplings of E. camaldulensis may be present.The most widespread shrub is Acacia dealbata.Callistemon sieberi is present along the OvensRiver, and Dillwynia cinerascens occurs along thegravelly banks of the Goulburn River. Theground-layer is a mosaic of grass-dominated com munities, with rushes (Juncus species), and sedges(Cyperaceae). The common grasses includeAgrostis avenacea, *Cynodon dactylon, Danthoniacaespitosa, D. duttoniana, D. racemosa, D. setacea,Paspalidium juborum, with Amphibromus nervosusand Pseudoraphis spinescens frequently commonon the wetter floodways (Plate 6M). The mostcommon sedges and rushes include Carex tereti caulis and Eleocharis acuta. Several species ofCyperus and ]uncus are common. Dicotyledonousherbs are frequently common locally, especiallyin damp depressions (e.g. Alternanthera den tz'culata, Brachyscome spp., Ca(Otis spp., Centipedacunninghamii, Craspedia spp., Crassula helmsii,Gnaphalium (sensu Lalo) spp., Isotoma jluviatilis,Polygonum spp., Senecio spp. and Stellaria caespi tosa). Areas of bare ground are common, andthe ground is usually littered with flood-carrieddebris.

In certain scattered and localized areas(e.g. Barmah and Gunbower State Forest) form er grasslands are being colonized by Eucalyptuscamaldulensis (Anon. 1983).

A lower E. camaldulensis open-forest (15-28metres high) occurs on drier sites amongst thetaller forest/woodland discussed above. Floris tically, these alliances are similar, except that inthe lower forest there is an increase in those spe cies that tolerate drier conditions (e.g. Elymusscabrus, Chloris, Danthonia and Stipa spp.) andfewer that prefer wetter conditions (e.g.Pseudora phis spinescens and other aquatic species). Exam ples occur on the Broken,'Campaspe and LoddonRivers, around swamps and lakes (e.g. nearBoort) and along many minor watercourses.

Periodic Hooding is an important, albeit com plex factor in seed germination in EucalyptuscamaLdulensis. Prolific germination of the seedsoccurs following the retreat of floodwaters inspring, but winter water temperatures are gen erally unfavourable for germination on floodedsites. Dexter (1978) discusses the relationshipbetween the various factors that are importantfor effective seed germination and seedlingestablishment for this species.

Riverina, open-forest

Riverina; open forest. Eucalyptus camaldulensis, with aquatic herbs Myriophyllum and Triglochin. Pseudoraphis spinescens grassland in background. Gunbower Island.

Eucalyptus largorens (Black Box)

Eucalyptus larorens-dominated open-forest to woodland (l0-28 metres high) occurs on the outer marginof the riverine E. camaldulensis forests (usually inthe less frequently inundated areas), along theMurray River as far east as Barmah, and is alsoassociated with some lakes and swamps. It oc curs mainly on grey, cracking clay soils that aremostly alkaline. It occurs on moderately salinesoils in some parts of the region (particularly inthe north-west). These soils support halophyticshrubs and herbs in the understorey. The E./argi/lorens community is most abundant in NewSouth Wales (Beadle 1981). This community iscomposed of either pure stands of E. larorens,or occurs in ecotonal association with E. camal dulensis or E. melliodora. The lower strata varyfrom being shrubby through to having a veryopen grassy ground-layer. The associated tallshrubs usually form a discontinuous stratum,with the most common ones being Senna spp.and Muehlenbeckia jlorulenta. Other shrubs thatmay be locally common include species of Acacia,Exocarpos and Myoporum. The dominant grassesinclude species of Danthonia and Stipa. Othercommon grasses include Agrostis avenacea,*Critesion hystnx~ and Homopholis proluta. Severalhalophytic plants are common, particularly inthe north-western parts of the region. Theseinclude species of Atrip/ex, Einadia, Enchylaenaand Rhagodia, plus Salsola kali. Other commonground-layer herbs include Chamaesycc drummon dn", Lythrum spp ., Marsilea drummondii (in moisterareas), So/anum esuriale and Vittadinia spp.

Eucalyptus microcarpa (Grey Box)

Eucalyptusmzc"rocarpa-dominated open-forest or woodland(mostly 15-28 metres high) originally coveredextensive areas of the plains, but now generallyoccurs as small remnants. E. microcarpa may occuras pure stands or in association with E. melliodora.E. camaldulensis may also be present. Allocasuarinaluehmannii is a common associate, especially onthe plains, whereas Eucalyptus blakelyi and E.macrorhyncha (the latter usually on better-drainedsites) are restricted associates (e.g. at Killawarra).The understorey is usually sparse, and com monly consists of Acacia acinacea, A. pycnantha,Bursaria spp., Cassinia arcuata and Eutaxia micro phylla. The major under-shrubs include Atn"plexsemibaccata, Enchylaena spp., Maireana spp., Ein adia hastata, E~ nutans and Sida corrugata. Theground-layer is dominated by grasses (e.g. Agrostisavenacea, Aristida spp., Danthonia caespitosa, D.duttoniana, D. linkii, D. pilosa, D. racemosa, D.setacea, Elymus scabrus, Poa spp., Stipa spp. andThemeda triandra). Species of introduced grassesare common (e.g. *Bromus, *Cn.tesion, *Cynodon,*Lotium and *Pha/aris) (Plate 6N).

This community also occurs on the drier mar gin and the internal sand-ridges of the riverineforests (Anon. 1983), and on the undulating areas near Rutherglen and Killawarra (in theeast of the region). Taller stands of this commu nity occur in the higher-rainfall areas, in theeastern parts of the region.

Eucalyptus melliodora (Yellow Box)

This com munity is very similar structurally and floristicallyto the Eucalyins microcarpa-dominated forestand woodland. E. melliodora tends to replace E.microcarpa in some hll-lier areas (e.g. MountMajor) and on sand-ridges (e.g. near Cobram)(Anon. 1983). Both communities have similarassociated species. E. b/akelyz" is frequently aco-dominant, and the resultant alliance formsmosaics with the E. albens community, with theformer occurring mainly on the river plains, thelatter on the adjacent undulating country andextending into the adjacent Midlands Region.Ca//itris glaucoby(la is commonly associated withthe Eucalyptus melliodora community, especiallyon sandy soils. E. melliodora tends to grow toa height of 15-20 metres. A taller open-forestcommunity (up to 30 metres high) occurs in thehigher-rainfall eastern parts of the region.

Riverina, woodland

Riverina; woodland. Eucalyptus melliodora and E. microcarpa, grassy woodland remnant, with sparse understorey including Acacia acinacea, Eremophila longifolia, Eutaxia microphylla, and grasses (Danthonia spp., Stipa spp. and exotics). Katamatire Reserve.

Eucalyptus blahelyi (Blakelys Red-gum)

Eucalytus blakelyi forms a woodland (5-15 metres high)to open-forest (up to about 30 metres high),with the latter occurring on more favourablesites. It occurs as pure stands or in associationwith E. goniocalyx, E. macrorhyncha, E. melliodora,E. microcar|)a and E. olyanthemos (e.g. in theRutherglen-Wodonga area). Much of the under storey of this community has been replaced byagricultural grasses or crops. Less disturbedexamples of this community occur in the neigh bouring Midlands Region.

Ca//itris glaucophylla (White Cypress-pine)

This woodland (IO-15 metres high) was oncewidespread across the plains of this region. Itusually occurred as a subdominant to Eucalyplusmicrocara or E. melliodora and Allocasuarina lueh mannii. It occurs with both Eucalyptus melliodoraand E. microcarpa in the Terrick Terrick StateForest (south-east of Pyramid Hill) on granite derived soils; in other areas it occurs on sandysoils (with E. melho~ dora)~ Callitris eissii also oc curs in the Terrick Terrick State Forest. Theunderstorey is either absent or is a sparse, opengrassland with sub-shrubs between the tussocks.Depending on the site, this community is floris tically similar to the woodlands dominated byEucalyptus blakelyi, E. melliodora or E. microcara.

Swamp and marsh communities

The effects of water regulation, raised salinewater-tables, and general agricultural practiceshave greatly modified the aquatic and semi..aquatic communities of the region. Three majorsubcommunities arc recognized (Anon., 1983).

Lignum swamps

At the time of Europeansettlement, communities dominated by Mueh lenbechia ]lorulenta were a feature of drainagechannels and swamps of _treeless plains (Anon.1983). The present distribution of Lignumlargely reflects land-use patterns. The effects ofwater regulation and increases in the soil salinityhave altered the distribution of this species. M.florulenta forms a more or less globular, tangledshrub (to a height of 2-3 metres), and may forman almost impenetrable thicket. This commu nity depends on regular flooding and a deeppenetration of water, hence it occurs in depres sions and along drainage lines, mainly in thewestern parts of the region. It usually occurs onstiff grey to black clay, mostly slightly alkalinesoils. Although trees are usually sparse, Eucalyptuslarorens and, to a lesser extent, E. camaldulen sis are often associated with these swamp com munities. Chenopodium nitrariaceum is commonlyassociated with Lignum. The common grassesinclude Agrostis aenacea, Danthonia spp. and Stiaspp. The other sub-shrubs and herbs are similarto those found in the Eucalytus lar orens dominated open-forest/woodland (see above).

Halophytic shrublands As for the Lignumswamps, the present distribution and floristicstructure of the halophytic shrublands largelyreflect current land-use practices. The area ofland affected by surface salt has increased greatlysince European settlement (Anon. 1983). Spe cies of the Chenopodiaceae and Aizoaceae arethe most common representatives of these shrub lands (e.g. *Galenia pubescens, Halosarcia spp.,Maireana spp., Salsola kali, Sclerostegia tenuis andSuaeda spp.). Other common species includeMuehlenbeckia jlorulenta and St"ipa spp. The den sity and composition of the community is in fluenced by soil salinity levels. This communityoccurs most extensively in the western part ofthe region.

Rush and sedgeland swamps A tall (up to 2metres high) closed-grassland/sedgeland occursin more or less permanent shallow water. Thissubcommunity is often dominated by Typha spp.and[or Phragmites australis. Typha spp. (e.g. T. dom z'ngensis) occurs in shallow water near the banksof rivers, in billabongs, farm dams, irrigationchannels (often as a serious weed) and in _deltaswamps (Beadle 1981 ). Juncus ingens forms ex tensive stands at Top Island (in the Barmah StateForest) and Lake Moodemere (both on the Mur ray River). A range of aquatic and semi-aquaticspecies are associated with these grassland[sedge lands, particularly in more open situations (e.g.species of Azolla, Cerus, Eleocharis,Juncus, Lemna,Potamogeton and Triglochin, and Ludwigia pep" loides and ()fichu ovalifolia).

Grasslands

Prior to European settlement, large areas of thisregion supported indigenous grasslands thatwere either treeless or sparsely wooded. Most of this community was quickly alienated for agri culture (Anon. 1983). Only scattered remnantsremain, and these have been usually greatlymodified by grazing, rabbits, and weed invasion.It is assumed that these grasslands were domin ated by species of Danthonia and Stipa. Grasslandsalso occur in areas where inundation preventstree growth, mainly in the riverine zone. Thecommon grasses include Amhibromus nervosus,*Cynodon daclon, Eragrost spp. and Pseudora pk spinescens. Other herbaceous genera that arecommonly present include Altemanthera, Carex,Centipeda and Dshania.

Land use

The region has been extensively cleared for thecultivation of cereal crops (mainly wheat, barleyand oats), livestock grazing (sheep and cattle),vineyards and orchards (the latter two occur inirrigated areas). Utilization of Eucalyptus camal dulenss for firewood, fencing, railway sleepersand harbour construction has a long history(Anon. 1983). Calli glaucohyIla has been usedfor house construction because it is termite resistant. Other eucalypt species have been usedfor fencing and firewood. Since settlement, theutilization of timber has been mainly restrictedto that which grows on public lands.

Considerable changes affecting the land andthe drainage patterns have occurred since Euro pean settlement. Initially, the natural vegetationwas selectively depleted by grazing pressure. Inthe late 1880s rabbit infestations further aggra vated soil erosion and pasture depletion. Large scale irrigation schemes for the production offodder crops, cereals, and fruit were establishedby 1890 on the Campaspe, Goulburn and Lod don Rivers (Butler et al. 1973). Problems of salin ity and waterlogging were evident soon afterirrigation began (as early as about 1910 in theKerang area). Irrigation activities have resultedin increased salinity levels in the Murray Riverdue to increased salt returns from the saliniza tion of surface soils (Collen 1978).

The various waterways are important recreational resources that are used for water-basedactivities (such as canoeing, shooting, swim ming, water-skiing, fishing, and bird-watching).An interesting summary of the vegetation, andassociated birds and mammals, for the BarmahState Forest, has been provided by Chesterfieldet al. (1983). Camping and bushwalking are alsoimportant outdoor activities. Many areas alongthe Murray River are intensively used for recrea tional purposes. Two such areas are the Barmahand the Gunbower State Forests (both providebreeding habitats for many birds and mam mals). Similarly, the other major rivers areintensively used for recreation.

National Parks

There are none in the region.

State Parks

Barmah-7900 ha; Leaghur -1580 ha.

Source: Conn, B.J. (1993) Natural regions and vegetation of Victoria, in: Foreman, D.B. and N.G. Walsh (eds), Flora of Victoria Volume 1, pp. 79–158, Inkata Press.