Robertson Rainforest in the Sydney Basin Bioregion - profile

Gazetted date: 05 Sep 2019

Profile last updated: 13 Nov 2024

The Robertson Rainforest ecological community is a type of warm to cool temperate rainforest characterised by a low, dense tree canopy, a mesic shrub stratum, lianas and a fern-dominated groundcover. It has a restricted distribution in the Southern Highlands of New South Wales, generally occurring on soils derived from basalt and basanite on the gently undulating Robertson Plateau and surrounds at altitudes between 500 and 800 metres above sea level. There are also small occurrences further south (e.g. on, and near to, the Sassafras Plateau, southwest of Nowra). The Robertson Rainforest in the Sydney Basin Bioregion is limited to the Sydney Basin IBRA2 Bioregion, from the Moss Vale, Illawarra and Ettrema subregions. It primarily occurs within the Wingecarribee local government area with some patches extending into the adjacent Kiama, Shellharbour and Shoalhaven local government areas (all as designated at December 2018). The principal occurrence of the ecological community is on the Robertson Plateau around the town of Robertson in the Southern Highlands. There are also some other less extensive occurrences nearby, including on the higher parts of the Cambewarra Range to the south of Robertson (NSW Scientific Committee 2011; NSW OEH 2017a) and on the Sassafras Plateau, southwest of Nowra (Mills 2019a, b & c; REPS 2019a; NPA 2019). The ecological community is found on highly fertile soils derived from Tertiary basalts, typically the Robertson Basalt but also others such as Kangaroo Valley Basanite and in transition zones between shale and basalt soils, at altitudes between 500 and 800 metres above sea level, on sites typically receiving high rainfall (1000–1600 mm per annum) (Mills & Jakeman 1995; NSW Scientific Committee 2011; NSW OEH 2017a). The following description of the vegetation generally relates to the less disturbed, or ‘reference’ condition, occurrences of the Robertson Rainforest. The species listed in this Conservation Advice are based on those identified as characteristic of the ecological community by NSW Scientific Committee (2011), updated and augmented with new information that has become available since that listing. The Robertson Rainforest in the Sydney Basin Bioregion is classified within the Southern Warm Temperate Rainforest 2 IBRA refers to the Interim Biogeographical Regionalisation of Australia. IBRA regions are large geographically distinct areas of similar climate, geology and landform with corresponding similarities in their vegetation and animal communities. The version current at the time of this advice is IBRA v7 (DSEWPaC 2013), which divides Australia into 89 bioregions and 419 subregions, including offshore islands. Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) vegetation class (NSW OEH 2017b). This class of rainforests generally comprises closedcanopied forests dominated by few tree species, over an open shrub layer, occasional lianas and epiphytes, and a dense ground layer of ferns. The Cambewarra Range basalt rainforest (Kangaroo Mountain Basanite) is more exposed and it does not get as cold as on the plateau to the north, so this part of the ecological community is more diverse (Mills, pers. comm., 2019b). The tree canopy of the ecological community is relatively low and dense (Tozer et al., 2010). The characteristic or common trees present include: Quintinia sieberi (Possumwood), Polyosma cunninghamii (Featherwood), Doryphora sassafras (Sassafras), Acacia melanoxylon (Blackwood), Syzygium smithii (syn. Acmena smithii) (Lilly Pilly) and occasionally Ceratopetalum apetalum (Coachwood) (NSW Scientific Committee 2011; NSW OEH 2017a; NSW OEH 2018a). The dominant species on the volcanics along the Cambewarra Range are different from those at the Robertson sites and may include Sassafras, Coachwood, Featherwood and Lilly Pilly, and additionally Pennantia cunninghamii (Brown Beech) and some subtropical species such as Dendrocnide excelsa (Giant Stinging Tree) and Citronella moorei (Silky Beech), with Sloanea australis (Maiden’s Blush) observed to be prominent at one site (Mills, 2019a). Common shrub species in the mid stratum include: Melicytus dentatus (Tree Violet), Coprosma quadrifida (Prickly Coprosma), Tasmannia insipida (Brush Pepperbush), Myrsine howittiana (Brush Muttonwood) and Notelaea venosa (Veined Mock-olive) (NSW OEH 2017a). There are also some components of the mid layer that are more typical of cool temperate environments, such as Olearia argophylla (Musk Daisy Bush), Hedycarya angustifolia (Native Mulberry) and Dicksonia antarctica (Soft Tree-fern). Various climber and epiphytic species may occur on the trunks and stems of canopy trees and mid-storey shrubs. Climbing species include Parsonsia brownii (Mountain Silkpod), Eustrephus latifolius (Wombat Berry), Marsdenia rostrata (Milk Vine), Pandorea pandorana (Wonga Vine) and Smilax australis (Lawyer Vine) (NSW Scientific Committee 2011; NSW OEH 2018a). Epiphytic species include the ferns Microsorum scandens (Fragrant Fern) and Pyrrosia rupestris (Rock Felt Fern) (NSW Scientific Committee 2011; NSW OEH 2018a). The ground cover typically comprises a dense cover of ferns and other herbs, including Lastreopsis acuminata (syn. Parapolystichum acuminatum) (Shiny Shield Fern), Lastreopsis microsora (Creeping Shield Fern), Microsorum pustulatum subsp. pustulatum (Kangaroo Fern), Asplenium flabellifolium (Necklace Fern), Pellaea falcata (Sickle Fern) and Urtica incisa (Stinging Nettle) (NSW Scientific Committee 2011; NSW OEH 2018a). 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.