Nestled between the expansive lawns and ornamental ponds of Sydney’s Centennial Park is a small wetland, fringed with sedges, known as Lachlan Swamp.

Its most impressive feature — not shared with many other bushland remnants in southern Sydney — is a dense canopy of swamp paperbark trees or Melaleuca quinquenervia.

Swamp paperbark trees (Melaleuca quinquenervia), Lachlan Swamp, Centennial Park, Sydney, 2019, photo by Rebecca Hamilton

Swamp paperbark trees (Melaleuca quinquenervia), Lachlan Swamp, Centennial Park, Sydney, 2019, photo by Rebecca Hamilton

As you enter this wetland forest, a raised, fenced boardwalk suggests that this flora is precious and sensitive to disturbance. A sign further along the trail confirms that the site protects remnants of important native flora characteristic of the Indigenous and early-British swamplands that once drained southward from the park to Kamay (Botany Bay).

This history is easy to believe given that all of the species present in the swamp today were certainly growing in Greater Sydney before the arrival of the British colonists in 1788. Yet the assumed ‘naturalness’ of the local swampland vegetation has not been empirically tested. This is a surprising omission given that the site is presented as an example of the ‘Sydney Freshwater Wetlands’, which are listed as an endangered ecological community under State environmental legislation.

My great-grandfather — who was almost fanatically devoted to cultivating exotic plants in his small but extremely colourful English garden — lived by the mantra that ‘the answer lies in the soil’. Carrying on the family legacy, I have become a specialist in a scientific field termed ‘palynology’ (literally the study of dust).

Lachlan Swamp, Centennial Park, Sydney, comparison of aerial photographs over time (source: NSW Department of Finance, Services and Innovation, 2018)

Lachlan Swamp, Centennial Park, Sydney, comparison of aerial photographs over time (Source: NSW Department of Finance, Services and Innovation, 2018)

Palynology is immensely valuable for reconstructing the vegetation history of an area over a long timescale — generally decades to millennia. It involves microscopic analysis of pollen grains produced by local plants that accumulate in layers of sediments through time.

Using this technique to test claims about the pre-European state of the Lachlan Swamp remnant in Centennial Park was the focus of my undergraduate honours project in 2010. After spending countless hours at the microscope and a large chunk of my supervisor’s annual research budget on radiometric dating, I demonstrated that the current paperbark forest at the Lachlan Swamp remnant only flourished at the site in the twentieth century. It replaced an open canopy, Epacridaceae-dominated heath- swampland. In this, my great-grandfather was right — the soil had clearly demonstrated that this little-known field of study could contribute significantly to improving environmental policy.

Feeling pleased with this discovery, I retreated to the Mitchell Library Reading Room to finish my thesis. It was here I came across several historic photographs, including an aerial photograph from the 1950s that provided a compelling answer to the question I had spent the better part of a year labouring over.

The photographs revealed that the vegetation of Lachlan Swamp was, within living memory, open and scrubby. This moment taught me that the information we need to conserve ecosystems — though typically viewed through the lens of science — may also be found in histories embedded in our libraries and museums, as well as in the memories of our Indigenous communities.

Since 2010 I have continued working as a conservation-focused palynologist in Australia and Southeast Asia. But the historical ecology of Sydney’s freshwater swamps has remained a key research interest for me. I recently found myself back in the Mitchell Library poring over historical maps, photographs and documents from south Sydney. This time, my aim was to piece together the nineteenth and twentieth century environmental history of the freshwater swamplands, and address unresolved questions about the conservation of these important ecosystems.

The wetlands of south Sydney were extensive, covering more than 11 square kilometres — six times the size of Centennial Park.

From a practical perspective, the misclassification of the ‘natural’ flora at Lachlan Swamp raises questions about conserving other remnant freshwater sites in south Sydney. Most of these sites have been corralled into narrow wetlands between Southern Cross Drive and adjacent golf courses.

I wanted to know how well represented this kind of landscape was before British settlement. Was the open heath at Lachlan Swamp an anomaly, or did it reflect the general composition of freshwater swamplands? If so, how extensive were these ecosystems?

I used mapping software to georeference and analyse more than 40 historical maps and plans of southern Sydney, many of which preserve information about the boundaries of water features and the topography of the landscape. This method has revealed that just after British colonisation the wetlands were extensive, covering more than 11 square kilometres — six times the size of Centennial Park.

This large network of swamps persisted through much of the early and mid-nineteenth century, despite being dammed for Sydney’s residential water supply and water-dependent industries. Urbanisation in the late-nineteenth and twentieth centuries had the largest impact on the water flows and size of the swamps, as bricks and concrete transformed the region from a city hinterland to an industrial, residential and transport hub.

Swamp areas shown in blue on 'Contour map of the country between Port Jackson & Botany Bay', 1894
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As I made digital comparisons of the topography of the region between the end of the nineteenth century and today, I could see how the swamplands had been constrained and their natural flows fragmented. Yet remnant waterbodies like Botany Dam and the Mill Pond (which, if you are looking, you can see from your car window on your way to or from the airport), and the somewhat diminished Lachlan Swamp in Centennial Park, have remained more- or-less continuous since 1788.

Paintings, photographs and written descriptions of the flora growing around the swamplands show that the nineteenth century landscape was characterised by open vegetation that was progressively cleared, converted, or buried under concrete in the century that followed.

This process mirrors what we see in the Lachlan Swamp pollen record, and in ongoing research conducted by the La Perouse Aboriginal community that draws on Indigenous ecological knowledge. Holistically, this work shows that open swamp heathlands were consistent and extensive across the region during the pre- and early British period.

Destruction of these swampland ecosystems was a dismissal of history as well as ecology. It ignored the distinctive botany that captivated Joseph Banks, James Cook and Daniel Solander in 1788, and led Cook to eventually give Kamay its colonial name — Botany Bay.

Urbanisation had the largest impact on the water flows and size of the swamps, as bricks and concrete transformed the region.

Early planning documents show a cycle in which British colonial authorities alternated between viewing the swamplands of southern Sydney as an unhealthy nuisance and as a valuable resource. They were under-regulated and exposed to highly polluting industries — such as wool washing and the boiling down of animal carcasses in the early nineteenth century, and chemical and paint manufacturing in the twentieth — with a period in between, from 1827 to 1896, when several of the swamps were over-utilised for their ‘abundant supply of soft, fresh, water’ (‘NSW Committee on the Tunnel’, 1837).

Such an erratic approach to managing and using the swamps over a short timeframe means that it is hardly surprising that once extensive Epacridaceae heathlands have largely been forgotten. The long-term legacy of human disturbance — based on society’s ever-changing values and economic interests — plays a large role in shaping contemporary ecosystems.

When we try to protect valuable ecosystems like Sydney’s freshwater swamplands, we must look beyond the short-term ecological evidence. Effective conservation requires a holistic, multidisciplinary approach that uses written and oral histories to complement scientific research.

Rebecca Hamilton is geographer based at the Max Planck Institute for the Science of Human History, in Jena, Germany, and is an associate investigator for the Australian Research Council Centre of Excellence for Biodiversity and Heritage. She was the 2019 Merewether Fellow at the State Library of NSW.

This story appears in Openbook Summer 2020.