1.1.7.1 Ecological systems

The eastern boundary of the bioregion is defined by estuary zones along the coastline, while the Great Dividing Range with the higher tablelands and ridges to the west form the western boundary, indicative of complex and varied vegetation communities and ecosystems. Seven river basins are defined within the bioregion (Figure 21) with hydrological summaries given in Section 1.1.5.

Of ecological importance to the Tweed river basin, although outside the bioregion, is Stotts Island and Ukerebagh Island in the Tweed estuary, with listing in A Directory of Important Wetlands in Australia (Environment Australia, 2001). Tweed estuary contains the largest remnant of lowland floodplain subtropical rainforest in New South Wales and Ukerebagh Island Nature Reserve protecting endangered communities of littoral rainforest, mangroves, saltmarsh and seagrasses in one of the largest estuarine wetlands (NSW Office Of Water, 2012). The river basin also contains Wollumbin (formerly Mount Warning) as the highest peak with an elevation 1156 m. Within the Richmond river basin the landscape varies from 100 m elevation to coastal floodplain, with the lower regions supporting extensive wetland areas, including Tuckean Swamp (NSW Office Of Water, 2012). The river basin has about 800 km² of land protected by national parks and reserves, especially in the north. Volcanic activity has played an important role in creating spectacular landforms and steep slopes of eucalypt forests with rainforest patches interspersed throughout leading down to lowlands and plains of forests and agricultural lands in the Richmond and Tweed river basins. The World Heritage Area Tweed Volcano group of the Gondwana Rainforests of Australia contains ancient rainforest plant and animal communities with evolutionary links to Gondwana. The area forms part of largest area of subtropical rainforest in Australia and has numerous national parks, such as Border Ranges National Park, Wollumbin National Park, Nightcap National Park, Toonumbar National Park and Richmond Range National Park and many forest reserves.

The Clarence river basin consists of tableland areas in the west that fall away to relatively large, flat floodplains towards the coast. The Clarence Lowlands supports saline basins, swamps and tidal delta flats in the main estuaries and meander plains, and backswamps, levees and terraces along the major drainage lines of the alluvial plain. The area has special conservation interest to state and federal governments (NSW Department of Environment and Climate Change, 2008) for its wetlands and remnant rainforest with particular ecological importance for its species diversity. Around 20% of the river basin is protected as national park and about 30% as state forest under a Regional Forest Agreement (Department of Agriculture, 2013).

The Upper Lockyer in the Brisbane river basin maintains forested hills with the mid and lower river basin largely cleared for intensive agriculture. Eucalypt-dominated communities exist in riparian zones and aquatic vegetation is poor, being mostly filamentous algae and Elodea species as aquatic ecosystems are being impacted by water overuse in this river basin. Unstable stream banks and gully erosion has resulted from removal or degradation of the riparian vegetation (DNRM, 2013). The Bremer River in the Brisbane river basin contains a highly turbid river with very poor water quality, resulting from industrial and domestic pollution, high nutrient concentrations and abundant bacteria. The river system has two significant wetlands: Purga Nature Reserve and Daly’s Lagoon near Ripley. Daly’s Lagoon has an endangered plant species – swamp tea-tree (Melaleuca irbiana) and a diversity of migratory wader birds. Lake Moogerah is a water supply and irrigation dam on Reynolds Creek, a tributary of the Bremer River. It is stocked with Australian bass, golden perch, saratoga, silver perch and Mary River cod, which is a significant investment for recreational angling (DNRM, 2013).

The Logan-Albert river basin is dominated by urban and agricultural land use, with the Logan River environmental condition rated as very poor due to high turbidity and degradation associated with land clearing. Urban (stormwater and sewage) and agricultural inputs dominate the upper and middle reaches of the river. The Logan River flows through subtropical rainforest onto fertile valley floors, becoming tidal about 60 km from its mouth and includes Lake Maroon and Wyaralong Dams. Stocking of the fish, such as Australian bass, golden perch, saratoga, silver perch and Mary River cod is taking place on Lake Maroon (DNRM, 2013). The Albert River within the river basin begins at Lamington National Park and flows through forested area into grazing and intensive agriculture and rural residential before joining the Logan River 11.2 km upstream from its mouth (DNRM, 2013). Riparian vegetation mainly consisted of Casuarina, Callistemon, Eucalyptus, Ficus and Lomandra species. Exotic species are also dominant (DNRM, 2013).