About the region

Among the varied bioregions along the east coast of Australia, Illawarra is a unique, but not disconnected, natural area. The Illawarra area has been defined at various times with various political, administrative and geographical boundaries. For this website, Illawarra is considered to be the area from Stanwell Park in the north to the Shoalhaven River in the south and from the ocean shoreline in the east to the Illawarra Escarpment crest as the western boundary (see Map 1 below). The centre of the area lies at 34.5° south latitude and the climate is mild maritime with moderate rainfall and moderate to warm temperatures. The region forms a distinctive geographical and floristic unit that differs from the adjoining Sydney Sandstone Basin to the north and the Shoalhaven Region to the south. The fertile soils, the mild climate and varied landforms create a range of habitats that favour a diversity of plants and plant communities ranging from seaside communities through eucalypt forests and woodland to rainforest.

The Illawarra region is home to a range of different vegetation communities, growing from the coastal strip, across the coastal plain and up the escarpment. Image by Leon Fuller.

Before Europeans arrived in the district, the natural vegetation was continuous and possessed an integrity and stability borne of thousands, or even millions, of years of evolution. Indigenous plants therefore have a strong affinity with the local conditions and without doubt are more adaptable to landscaping and revegetation than most introduced plants.

Map 1: The area covered by this website. Some places mentioned on the website are included.

How it was

Before large-scale land-clearing by Europeans, the district was largely covered in sclerophyll forest, mostly dominated by eucalypts. There was (and still is) a strong component of rainforest and smaller areas dominated by shrubs and trees such as Coast Tea Tree along the coastline edge and some melaleuca shrubland and forest across the coastal floodplains. The patterns that various plant communities formed were a reflection of the combined physical and biological features of the district.

Aboriginal Australians have lived in the region for tens of thousands of years. Their interactions with and use of the land, plants and animals may have had an influence on the region's vegetation over time. Michael Organ's Illawarra and South Coast Aborigines (Volume Two available here) provides an important compilation of historical documents and records of Aboriginal Australians in the region for the period from 1770 onwards.

The plants of the coastal strip often possessed small, succulent or hairy leaves and stems and other features which enabled them to tolerate the strong salt-laden winds and the freely draining sandy soils.

Wetlands, swamps and saltmarsh abounded in Illawarra even as recently as the 1950s. Apart from Lake Illawarra, a most conspicuous wetland was Tom Thumb Lagoon that stretched from the sand dunes of South Wollongong Beach across to Springhill Road and from Swan Street Wollongong, right down to the blast furnaces of the steel works, a length of 3km and a width of 2km. Tom Thumb Lagoon was filled in to make room for the industry of Port Kembla. There were also large wetlands at Thirroul, Bellambi, Towradgi, Warilla, Gerringong, Seven Mile Beach and the huge area of the lower Broughton Creek catchment. These have all been drained or filled, profoundly affecting local ecological communities. The ecology, the plants, and the populations of animals and birds from these areas are either greatly modified or no longer exist.

The coastal plain is undulating and is crossed at regular intervals by creeks and rivers draining from the escarpment. The floodplains were originally covered by eucalypt and melaleuca forests often with a grassy understorey or scattered rainforest plants that would increase in size and density in the absence of fire for long periods. The grassy understorey was a fortuitous bonanza for early settlers on which to graze their cattle. The undulating terrain also provided conditions on which an industrial and residential city could develop.

Riparian vegetation existed adjacent to the short rivers and creeks flowing eastward across the coastal plain before land clearing took place. A characteristic group of species inhabited the riparian zones although these species would have occurred elsewhere in different combinations in other communities. The coastal plain from just north of Lake Illawarra to Gerringong is underlain by varying-sized areas of volcanic rocks which increase the fertility of the soil and allow different plant species and communities to grow.

The escarpment rising in the west is a strong feature of the Illawarra landscape. Its height alters the climate of the area, pushing on-shore winds up causing higher precipitation and lower temperatures with increasing elevation. The orientation and height of the escarpment also affords protection on the slopes against strong drying winds from the west. With cooler temperatures, greater water availability and moderately fertile soils, the escarpment was, and still is, home to extensive subtropical and warm-temperate rainforest as well as tall eucalypt forest.

The escarpment cliffs and the areas underlain by Hawkesbury Sandstone to the west are not included in this website. Much information is already available on growing plants of the Sydney Sandstone Basin. Except for the sandy beach fringe, most of the soils across Illawarra have a fairly high clay content which endows them with moderate fertility and good water-holding capacity - a major reason for the prevalence of rainforest and a generally richer vegetation.

How it is now

The present picture of Illawarra shows a coastal strip which has been largely cleared of its original vegetation leaving naked beaches and residences along the waterfront that in efforts to retain “ocean views” maintain little vegetation other than Kikuyu grass and other low-growing introduced species.

The coastal plain around Wollongong and Fairy Meadow, as seen from the summit of Mount Keira. Development has displaced most of the native vegetation. Image by Leon Fuller.

The coastal plain, being flat or undulating in nature was ideal for grazing and agriculture and later in the development of the district also became ideal for industrial and residential development. Therefore it was cleared extensively so that little remains of the original vegetation, particularly the riparian corridors along rivers and creek. The riparian vegetation very likely had a large component of rainforest trees and rainforest communities; they have virtually all gone. The vestiges of grassy woodland and melaleuca forests that still exist on the floodplain are also presently under threat of extinction.

Urban development on the coastal plain is densest between Austinmer and Dapto. West Dapto, Albion Park and southwards there remain broad areas of rural land that retain natural vegetation along some creeks and fragments of forest in certain areas.

In the view north from Saddleback Mountain, rural lands are interspersed with areas of remnant vegetation. Image by Leon Fuller.

The lower slopes of the escarpment have been greatly altered by land clearing for agricultural use at first and residential development in more recent times. These footslopes, with their deep and fertile soils, are still a location where horticultural pursuits are easy and rewarding. The use of indigenous plants, especially rainforest species is particularly warranted and useful here.

Again, urban development on the footslopes is most intense in the northern part of the district and south of Mount Kembla there are still large areas of original vegetation that now provide a resource for natural area preservation.

The upper slopes are quite steep and unsuitable for development and little alteration has taken place. The original forest is still strong with warm temperate rainforest being common and eucalypts are those that form tall, cool wet sclerophyll forest.

Vegetation zones of Illawarra

This website divides the Illawarra region into a number of vegetation zones. The divisions are based on broad physical and ecological similarities within, and differences between, zones.

Map 2: Vegetation zones of Illawarra.

The zones detailed on this map are approximations because of the small scale of the map. In the cases of sandy seaside areas, seacliffs, hind dunes, saltmarshes, and riparian areas, the exact boundaries of the communities have not been mapped.

There are a number of different types of igneous rocks through the area including the basalt-like latite, volcanic sandstones, tuffs and so on, but these have been grouped together as volcanic throughout the website. Divisions between specific areas of volcanics and their adjacent parent rocks and attendant plant communities are also too complex to map at this scale. So the map and vegetation zones should be used as a general guide only.

Fortuitously, most of the plants referred to on this website are adaptable and naturally grow in many of the local plant communities, so accuracy in following natural ecological trends is not essential. However, where possible, for good results in planting, choose indigenous species with environmental preferences that suit the site; this is especially relevant with specialised plants like water plants, saltmarsh or beach plants.

The Coastline Strip is the narrow band along the seafront that is subject to oceanic influences. It is made up of the following vegetation zones: Sandy Seaside areas, Seacliffs, Hind Dunes and Saltmarsh. Being subdivisions of the coastline strip they are not separately marked on the map because of the difficulty in defining them at such a small scale. However, the various zones are choices in the search criteria on the home page.

The plants of the coastline are all usually exposed to strong winds off the ocean as well as a high salt content in the mist/spray they carry. The plant species that grow naturally in this coastline strip are all adapted to these conditions.

This image shows Seven Mile Beach, with the sandy seaside areas, lagoon and hind dunes also visible. Image by Leon Fuller.

Sandy seaside areas. Beaches and hind dune areas basically have soils made up of sand and they are exposed to winds from the ocean, that are sometimes very strong and often laden with salt. Salt can be harmful for plants but also provides some nutrients. The humidity of the ocean also can favour some plants, exemplified by ferns growing on seacliffs such as Coral Fern (Gleichenia rupestris) near the Continental Pool, North Wollongong and at Austinmer.

Hind dunes are seaside areas that generally have sandy soils and are located behind dunes where there is some protection from strong onshore winds. They naturally support a wide range of plants including rainforest species.

Littoral rainforest growing on hind dunes at Gerroa. Image by Peter Woodard, reproduced from Flickr under Creative Commons license BY-NC 2.0 (https://www.flickr.com/photos/17674930@N07).

Seacliffs mostly have soils made up from the underlying rocks or may include the underlying rocks themselves. Seacliffs may have soils of sand overlying clay or sand as a major fraction of the otherwise clayey soil. Seacliffs in some cases, such as along the Kiama coast, are also formed from igneous (volcanic) outcrops.

Saltmarsh is largely associated with the edges of estuaries and lagoons along the coastline strip, including various places around the shore of Lake Illawarra. Water levels often fluctuate and have varying degrees of salinity. It is a particular set of species that can tolerate these conditions. Not all saltmarsh species are suitable for horticultural use. However, among them are some interesting and beautiful plants worthy of attention, such as Swamp Weed (Selliera radicans), Knobby Club Rush (Ficinia nodosa) and Australian Gypsywort (Lycopus australis).

Tidal flats with fringing saltmarsh vegetation, near Shoalhaven Heads. Image by Katie Wright.

Succulent plants such as Austral Seablite (Suaeda australis) often occur in coastal saltmarsh. This image was taken at Wollomai Point in Berkeley. Image by Tony Rodd, reproduced from Flickr under Creative Commons license BY-NC-SA 2.0 (https://www.flickr.com/photos/tony_rodd).

Wetlands encompassing estuaries, lagoons and freshwater lakes and streams as well as being the ecotone between water bodies and adjoining swamps. These are not marked on the map because of the difficulty in mapping at this scale; their size and condition may vary across rainy-to-dry seasons.

A managed wetland. Image by Carl Glaister, reproduced under Creative Commons license BY-NC 2.0.

Coastal plain in Illawarra basically means the floodplains and hills that lie between the sandy coastline zone and the escarpment footslopes. The floodplains are usually made up of quarternary alluvium and the soils on higher ground are usually derived from underlying rocks of Coal Measures and Broughton Formation with some volcanic influences. From Thirroul to the Shoalhaven River the plant communities vary on the Coastal Plain from tall wet sclerophyll forest dominated by Blackbutt (Eucalyptus pilularis) through dryer Grassy Woodland dominated by Forest Red Gum (Eucalyptus tereticornis) and other eucalypts, to melaleuca communities.

The coastal plain is home to a number of threatened ecological communities, including Illawarra Lowlands Grassy Woodlands that occur in tiny, vulnerable pockets such as Wisemans Park and larger areas like Croom Reserve. Image by Emma Rooksby.

Riparian zones differ from swamps and wetlands in that the soil is not saturated with water and they are located beside creeks and streams where there is a good availability of water and also often good protection from wind and sun allowing particular plants to thrive. Riparian zones meander across the coastal plain along with water courses but riparian plant communities are distinctly different to floodplain communities even though they may have some species in common. They often support rainforest species or even rainforest ecological communities.

A mixture of sclerophyll and rainforest plant species line this creek in Mount Pleasant. Image by Emma Rooksby.

Escarpment. Throughout the length of the escarpment, the underlying geology and the structure and arrangement of plant communities is far too complicated to describe here. For the sake of simplicity, the escarpment is divided into upper and lower categories. The upper escarpment generally contains a high percentage of warm temperate rainforest and the lower escarpment generally has mostly subtropical rainforest, but varying degrees of overlap exist. The descriptions of individual plant species include more detailed information about where they prefer to grow.

Mount Keira, one of the most distinctive parts of the Illawarra escarpment, as seen from Wollongong
Botanic Garden. Image by Tony Rodd, reproduced from Flickr under Creative Commons license BY-NC-SA 2.0 (https://www.flickr.com/photos/tony_rodd).

The lower escarpment is not homogeneous from one end of Illawarra to the other. In the north the underlying rocks are sedimentary whilst the southern part there is a strong influence of volcanics. The lower escarpment generally has gentler slopes than the upper escarpment. The soils are deeper and generally more fertile than the coastal plain and rainfall is higher on the escarpment than on the coastal plain. Residential development has pushed into the lower escarpment and because of the physical conditions, there are great opportunities for growing a wide range of plants, especially those indigenous to Illawarra and to the escarpment.

Upper escarpment areas have not suffered much agriculture or residential development. Correspondingly there is presently no great need for revegetation in the form of gardening or bush regeneration except in the area west of Berry. Information contained in this website is only applicable on the escarpment up to the base of the Hawkesbury Sandstone cliffs. So only a handful of the species in the website that grow east of the escarpment cliffs are relevant to Hawkesbury Sandstone areas and vice versa.

Some species included in this website naturally occur only in the higher parts of the escarpment. These include Possumwood (Quintinia sieberi) and Brush Pepperberry (Tasmannia insipida). Many of the species that occur lower on the escarpment can also occur higher.

Volcanic zone. Areas where volcanic rocks outcrop are scattered through the Illawarra especially in the Kiama district and along the escarpment from Saddleback Mountain to Cambewarra Mountain. So while the volcanic zone is shown on the map, it is only the part of the district where volcanic outcrops and soils are common. Other soils and plant communities exist in these areas too, but the influence of the volcanics is significant. Berkeley Hills is one continuous volcanic area from the railway line at Unanderra to Hill 60 in Port Kembla.

Note that the lower escarpment west of Berry is largely underlain by an igneous (volcanic) outcrop but on Map 2 it is designated as lower escarpment rather than as volcanic.

You can use this website to explore the plants that grow in different vegetation zones by using the plant finder tool to search by zone.