Swamp Oak Floodplain Forest

Sydney Olympic Park supports approximately 5 hectares of Swamp Oak Floodplain Forest (SOFF), an endangered ecological community. Some stands of this community have established naturally within the Park. In other areas, stands of this community have developed from planted trees.

The largest stand of the community occurs within Newington Nature Reserve, to the south of Main Lagoon where it lies between the Coastal Saltmarsh and Sydney Turpentine Ironbark Forest communities, and has established since 1955. Small areas also occur in other parts of the Reserve, within Newington Armory, along Haslams Creek, and within Badu Mangroves.

SOFF is an ‘ecological community’ – an integrated assemblage of trees, shrubs, herbs, grasses and fungi, mammals, birds, amphibians, invertebrates and micro-organisms.

The SOFF community occurs on the coastal floodplains of NSW. It typically forms mosaics with other floodplain forest communities and wetlands, and often fringes treeless wetlands with semi-permanent standing water, such as Main Lagoon in Newington Nature Reserve. The most saline forms of SOFF may adjoin or intergrade with Coastal Saltmarsh. The boundaries between these communities are dynamic and may shift in response to changes in hydrological regimes, fire regimes or land management practices.

SOFF has a dense to sparse tree layer in which Casuarina glauca is the dominant species northwards from Bermagui. Other trees including Acmena smithii and Melaleuca spp. may be present as subordinate species, but are found most frequently in stands of the community northwards from Gosford. Tree diversity decreases with latitude. The understorey is characterised by frequent occurrences of vines, a sparse cover of shrubs, and a continuous groundcover of forbs, sedges, grasses and leaf litter. The composition of the ground stratum varies depending on levels of salinity in the groundwater.

At Sydney Olympic Park, the Swamp Oak Casuarina glauca is the only canopy species present; dominant understorey and groundcover species are Myoporum boninense and Cupaniopsis anacardioides, and Juncus kraussii, though generally these strata are poorly developed.

Faunal components of SOFF are poorly documented but both vertebrate and invertebrate assemblages can be diverse. The community sometimes provides food resources for the Yellow-tailed Black Cockatoo Calyptorhyncus funereus and the threatened Glossy Black Cockatoo Calyptorhynchus lathami lathami (although the latter has not been recorded to date at Sydney Olympic Park). Several species of microchirpoteran bats have been recorded foraging and roosting within the forest at Sydney Olympic Park, particularly the Lesser Long-eared Bat Nyctophilus geoffroyii.

Conservation significance

SOFF was listed as an ‘endangered ecological community’ under the NSW Threatened Species Conservation Act 1995, in 2004.  An ‘endangered ecological community’ is one that is likely to become extinct in nature in NSW unless the circumstances and factors threatening its survival cease to operate.

Although SOFF occurs on floodplains throughout coastal NSW, it has been extensively cleared and modified. The remaining area of this community is considered likely to represent much less than 30% of its original range.  It was estimated in 1998 that only about 13% of this community remained on the Cumberland Plain of western Sydney.

The remaining stands of SOFF are severely fragmented by past clearing. Small areas of SOFF are contained within existing conservation reserves including Newington Nature Reserve, but these occurrences are unevenly distributed throughout the range of the community and are unlikely to represent its full diversity. Very few examples of SOFF remain unaffected by weeds.

The community at Sydney Olympic Park has few weeds, and forms part of a rare example of complete estuarine zonation of Eucalypt forest, Casuarina forest, Coastal Saltmarsh and Mangroves.

Management

Weed control using bush regeneration techniques has been practiced for the past several years, with the result that there is now a very low level of weed infestation. In 2005, mowing ceased within part of the Newington Armory buffer zone, to promote expansion of the community.

During 1999/2000, Casuarina glauca were planted within parts of what is now Newington Nature Reserve following wetland remediation works. There is no documentation of the provenance of the Casuarina glauca plantings within the Reserve, though some local seed was collected and propagated for use in the extensive planting programs underway across Sydney Olympic Park at that time.

The majority of the Park’s Swamp Oak Floodplain Forest is fenced within Newington Nature Reserve; public access to this area has been restricted since the community developed. Re-introduction of tidal flushing to the Newington Nature Reserve wetland in the late 1990s initially caused some die-back of canopy trees. Forest health has since improved, following adjustment of the hydrological regime.

Casuarina glauca has been widely used in landscape plantings across Sydney Olympic Park since the 1990s. Planted stands and individual trees of Casuarina glauca in terrestrial areas are not currently considered to comprise the Swamp Oak Floodplain Forest community. Some plantings in estuarine areas, including Newington Nature Reserve may develop into this community over time.

Casuarina glauca is a highly invasive species that spreads by suckering and seeding, and is actively controlled in many parts of the Park where it poses a threat to other native species and communities such as Coastal Saltmarsh and Green and Golden Bell Frog habitat.

The Authority undertakes strategic mosquito management across many of the Park’s estuarine wetlands, by aerial and ground-based application of a biological larvicide.

Where to see Swamp Oak Floodplain Forest

The Swamp Oak Floodplain Forest of Sydney Olympic Park can be seen at:

• River Walk at Newington Armory
• pathways at Badu Mangroves

Help to protect and conserve Swamp Oak Floodplain Forest by staying on the paths.