MVG 8 Casuarina Forests and Woodlands DRAFT
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MVG 8 - CASUARINA FORESTS AND WOODLANDS Calcareous sandplain woodlands, western NSW (Photo: B. Pellow) Overview Casuarinas (the she-oaks) are a distinctive part of the Australian landscape. The name Casuarina is derived from the Malay Kasuari and alludes to the similarity between the drooping foliage of some species in the genus and that of the feathers of the cassowary bird (Boland et al., 1994). Casuarinas have a unique leaf structure, in which individual leaves are reduced to small teeth, the bases of which are fused and surround the stem. This gives the leaf-bearing branchlets the appearance of needles and the plant canopies a fine structure allowing permeability of more light than broad-leaf tree canopies. While several contrasting vegetation types are dominated by Casuarinas, most species of Allocasuarina are subordinate or subdominant members of mixed plant communities. MVG 8 includes vegetation dominated by Casuarina or Allocasuarina in contrasting environments such as arid sandplains, coastal floodplains and riparian corridors in humid landscapes (Keith 2004). Casuarina vegetation not included within MVG 8 includes: Allocasuarina decaisneana open woodland of the central deserts (included within MVG 31); coastal scrubs dominated by Allocasuarina equisetifolia (included within MVG 15); and small areas dominated by dense stands of Allocasuarina littoralis within dry sclerophyll eucalypt forests (included within MVG 3). Facts and figures Major Vegetation Group MVG 8 - Casuarina Forests and Woodlands Major Vegetation Subgroups ##. Eastern floodplain/estuarine forests NSW, QLD (number of NVIS descriptions) ##. River oak forests ACT, NSW, QLD 26. Calcareous sandplain woodlands NSW, VIC, SA Typical NVIS structural formations Woodland (tall, mid, low) Open woodland (mid, low) Number of IBRA regions 57 Most extensive in IBRA region Est. pre-1750 and present: Great Sandy Desert Estimated pre-1750 extent (km2) 166 303 Present extent (km2) 149 262 Area protected (km2) 27 561 Eastern floodplain/estuarine forests western Sydney, NSW (Photo: B. Pellow) Structure and physiognomy Dominated by Casuarina species often in monospecific stands or otherwise with infrequent co- dominants. The tree Casuarina species that dominate the subgroups reproduce vegetatively by suckers to varying degrees. In semi-arid regions ephemeral plant species are an important component of this MVG. In riparian and estuarine environments, tree canopies may reach 20 - 30 m tall with 30 40% canopy cover, sometimes producing a deep layer of casuarina ‘needles’ can occur limiting the growth of shrubs and ground layer species. Some stands, however, have a conspicuous ground layer of moisture-tolerant forbs and sedges or rushes. The canopy of this MVG tends to be sparser in the semi-arid areas than in moist environments, permitting the development of an open shrub layer and ground layer of perennial and ephemeral forbs and grasses. Trees are typically around 12 m tall with a canopy cover of >10% and the understorey includes an open layer chenopod or other shrubs - (Victorian Department of Sustainability and Environment 2015). Indicative flora Although MVG 8 is dominated by tree species from the same family with a superficially similar appearance because of their structurally similar canopies, it includes plant assemblages from very different environments with contrasting ecology and few species in common. These are classified into three major vegetation subgroups. o Eastern floodplain/estuarine forests are dominated by Casuarina glauca either in pure stands or mixed stands with Melaleuca styphelioides, Melaleuca quinquenervia or Melaleuca ericifolia. Canopy and understorey composition varies with frequency of inundation, soil texture, salinity and latitude. Occasional shrubs include Glochidion ferdinandi and Myoporum acuminatum. The groundlayer includes a varying mixture of forb genera such as Alternanthera, Commelina, Persicaria, Solanum and Viola, and graminoids including species of Baumea, Carex, Cynodon, Gahnia, Juncus, Lomandra, Microlaena and Phragmites (Keith 2004). o River oak forests are found in the narrow riparian zones of streams draining both sides of the Great Dividing Range. Casuarina cunninghamiana dominates the tree layer, although various eucalypts from surrounding forests and woodlands may co-occur in low densities. Although the species distribution extends to tropical Queensland and the Northern Territory, at those latitudes it tends to be part of more diverse riparian communities. In forested landscapes further south and east of the Great Divide it may have a subcanopy of Tristaniopsis laurina or rainforest species and can be replaced by them along smaller faster-flowing streams. West of the Great Divide Casuarina cunninghamiana may co- occur with Eucalyptus camaldulensis and is replaced by it further downstream. The understorey is generally sparse and interspersed with alluvial debris, with many of its plant species reflecting influence from surrounding vegetation. Common riparian graminoids include Lomandra longifolia and Carex appressa, with forbs such as species of Alternanthera, Aneilema, Hydrocotyle and Persicaria (Keith 2004). o Calcareous sandplain woodlands occupy sandplains in semi-arid south-eastern Australia. Casuarina pauper dominates the most extensive expressions of this subgroup, usually in pure stands and often with a subcanopy of Alectryon oleifolius. On sandhills the woodlands may include Myoporum platycarpum, Callitris glauca, Callitris murrayana or Allocasuarina luehmannii, with these species replacing Casuarina pauper in higher rainfall areas and/or where the calcrete subsoil is deeper or absent (Victorian Department of Sustainability and Environment 2015). In the northeast of its range, Casuarina pauper may co-occur and hybridise with Casuarina cristata, although that species is commonly associated with Brigalow Forests and Woodlands within MVG 6 and in relatively small areas where it dominates, the structure and composition are more closely aligned with Brigalow communities (Neldner et al. 2014). Around the Nullarbor plain and in Western Australia, Casuarina pauper becomes part of Acacia woodlands (MVG 13). Understories are often dominated by chenopod shrubs and forbs including species of Maireana, Chenopodium Enchylaena, Rhagodia and Sclerolaena. Other shrub genera such as Eremophila, Exocarpos, Geijera and Olearia dominate other stands. The ground layer includes ephemeral species of Asteraceae and Zygophyllum with tussocks of Austrostipa, Chloris, Enneapogon, Chloris and Sporobolus (Keith 2004; Victorian Department of Sustainability and Environment 2015). Environment The subgroups of MVG 8 occur in contrasting environments. Eastern floodplain/estuarine forests occur on periodically inundated subsaline flats associated with lower floodplains and estuarine fringes. They occur in mosaics with other floodplain forests on their upper reaches (MVG 3), Melaleuca forests (MVG 9) or coastal saltmarshes (MVG 22) at their tidal extremity. River oak forests are restricted to alluvial soils along riparian corridors of largely permanent streams draining the Great Dividing Range at altitudes up to 800 m. Periodic floods create gaps and initiate recruitment in both overstorey and understorey species. Calcareous sandplain woodlands occur on calcareous sandplains in semi-arid climates receiving mean annual rainfall of 220-350 mm. The soils are solonized sandy loams with calcrete nodules in the subsoil. These woodlands occur in landscape mosaics with mallee woodlands (MVGs 14 and 32) and bluebush shrublands (MVG 22). In South Australia and Tasmania Allocasuarina verticillata forms monospecific stands on a range of topographies from hill slopes and crests to coastal dunes and plains. The coastal dune assemblages belong to MVG 15. Examples can be found in the Flinders Ranges and on Kangaroo Island in South Australia and in inland drier areas and coastal areas of Tasmania (Harris and Kitchener 2005; Government of South Australia 2015; NVIS version 4.1). Geography MVG 8 is located primarily in eastern Australia. Eastern floodplain/estuarine forests are distributed on the east coast lowlands between 23° and 37° S latitude in southern Queensland and New South Wales. River oak forests occur along major streams draining the Great Divide between approximately 23° and 37° S latitude in southern Queensland and New South Wales (Keith 2004). Calcareous sandplain woodlands are found on extensive calcareous sandplains of the lower Murray-Darling basin, extending west to the Nullarbor plain in southwest New South Wales, northwest Victoria and southern South Australia (Beadle 1981; Keith 2004; Victorian Department of Sustainability and Environment 2015). Change Approximately 10% of the estimated pre-1750 extent cleared accounting for 1.7% of total clearing in Australia. Approximately 17 000 km2 cleared since European settlement. Eastern floodplain/estuarine forests have been greatly depleted by clearing for intensive agriculture. The remaining areas are primarily in the most saline environments associated with estuaries (Keith 2004). Changes to floodplain drainage have further modified the distribution of floodplain vegetation. Soil oxidation related to ditching has resulted in dense regrowth of Casuarina glauca in locations where it may not have previously occurred, but rarely with the range of other species characteristic of the native forests. Invasions by weeds associated with fertiliser use in catchments and disturbance