Illawarra-Shoalhaven Subtropical Rainforest of the Sydney Basin Bioregion - profile

Gazetted date: 05 Sep 2019

Profile last updated: 25 Oct 2022

The ecological community combines two New South Wales (NSW) state listed endangered ecological communities: The ‘Illawarra subtropical rainforest in the Sydney Basin Bioregion’ (NSW Scientific Committee 2002a) and the ‘Milton Ulladulla subtropical rainforest in the Sydney Basin Bioregion’ (NSW Scientific Committee 2002b). The Illawarra–Shoalhaven subtropical rainforest ecological community occurs south of Sydney in NSW, in the Sydney Basin IBRA3 Bioregion. It occurs in the Illawarra, Jervis and Sydney Cataract (SYB12, SYB14 and SYB10) IBRA subregions, and just over the borders into Burragorang (SYB09), Moss Vale (SYB11) and Ettrema (SYB13) subregions; it may also occur elsewhere in the Sydney Basin Bioregion, in other subregions. The majority of the ecological community occurs in the Illawarra IBRA Subregion (SYB12). The ecological community’s northern boundary of occurrence is the Port Hacking estuary. Its southern boundary is the boundary between the Sydney Basin and the South East Corner IBRA bioregions. It occurs on the coastal plain, low-lying foothills and slopes, benches and drainage lines of the eastern coastal escarpment (and of some coastal mountains), between the Hacking and Clyde rivers. It rarely extends onto the upper escarpment slopes. It is usually found below 350 m above sea level (ASL); but there are occurrences up to around 550 – 600 m ASL, for example around Cambewarra Mountain. Much of the ecological community occurs between Stanwell Park and Gerringong (where it was termed the Illawarra Brush6 by Mills & Jakeman (1995)). It continues south to the Shoalhaven River; and westwards into Kangaroo Valley and around gorges of the Ettrema region and Toorooroo Plateau (Mills 2010). Further occurrences of the ecological community are found around Milton and Ulladulla (approximately 50 to 70 km to the south). The ecological community is typically associated with the more fertile (higher nutrient)7 soils associated with coastal Permian and Triassic igneous rocks, including: Gerringong Volcanics, Cordeaux Crinanite and exposed latite on slopes and enriched, colluvial8 benches of the Illawarra escarpment. It also occurs on sedimentary rocks such as Budgong Sandstone on the escarpment foothills and the coastal plain and on Illawarra Coal Measures and Narrabeen Group shale on the escarpment benches and where dissected in deep, sheltered gullies (e.g. where the Hacking River has cut down from sandstone into the shale) 10. In the Milton– Ulladulla district, the ecological community typically occurs on Milton Monzonite11, as well as on deep alluvium and soils of the Conjola Formation enriched by monzonite; and it also occurs widely on skeletal exposed monzonite (Tozer et al. 2010). At the time of this assessment (2018–19), the ecological community is known to occur in the South East Local Land Services (SE LLS) Natural Resources Management Region. It has been recorded in areas in the Local Government Areas (LGAs) of Kiama, Shellharbour, Shoalhaven, Sutherland and Wollongong; and may occur nearby, in adjacent LGAs such as Goulburn Mulwaree and Wingecarribee. Other wet forest and rainforest vegetation communities occur in this region, and their relationships to the ecological community are detailed in Section 3.4.3 and Appendix D. The following description of the vegetation generally relates to the less disturbed, or ‘reference’ condition, occurrences of the Illawarra–Shoalhaven subtropical rainforest. The species listed in this Conservation Advice are based on those identified as characteristic of the ecological communities listed in NSW by the NSW Scientific Committee (2002a; 2002b), updated and augmented with new information that has become available since those listings. Many patches of the ecological community have been disturbed, with fire, temporary clearing, logging, grazing and ‘under-scrubbing’ having exerted a strong influence on the structural and floristic composition of the ecological community (Mills & Jakeman 1995; Tozer et al. 2010). Some patches, which would have been part of the ecological community, are now so modified that they no longer meet the Key diagnostic characteristics or minimum Condition thresholds (in sections 3.1 and 3.2) for the nationally protected ecological community. The Illawarra–Shoalhaven subtropical rainforest ecological community is typically a dense, complex rainforest when mature (12 to 25 m tall), with an emergent tree layer up to 35 m or more in height (Mills & Jakeman 1995). In some circumstances, e.g. on dry, rocky sites, the canopy may be shorter. The ecological community is characterised by its relatively high structural and floristic diversity. At a local scale, its expression/structure can vary depending on soil fertility and also moisture availability (due to either rainfall, aspect, topographic position or soil depth), or some combination of these factors. The ecological community is generally a low to moderately tall closed rainforest. It has a dense mixed tree canopy (canopy cover typically =70% on average for a patch in relatively good condition) and a sparse shrub layer (Mills & Jakeman 1995). The groundcover is often sparse, except in moister areas (Tozer et al. 2010). At lowland sites, particularly on latite, the ground can be largely covered by rock, often with little soil being visible (Mills & Jakeman 1995); as opposed to bench sites on the escarpment, where ferns are usually abundant and there are few surface rocks. Tree species with compound leaves are common and leaves are relatively large (notophyll to mesophyll). There is a relatively low abundance of species from the genera Syncarpia, Acacia, Banksia and Eucalyptus (unlike the Littoral Rainforest and Vine Thickets ecological community, where these genera may be more commonly present). Buttresses may be common and vines may be diverse and abundant. In order to meet the definition of the TEC sites must satisfy condition criteria stipulated in the Listing Advice and/or Conservation Advice. Typically condition is assessed by reference to patch size and vegetation structure thresholds or species composition metrics.