Human environmental impact and the Aboriginal abandonment of Kangaroo Island

A project undertaken at The University of Sydney and supervised by Stephen Gale

The first Europeans to arrive on Kangaroo Island found a land bereft of people and occupied by extraordinarily tame marsupials that appeared to have grown accustomed to the absence of human predation. Yet the subsequent discovery of Aboriginal artefacts showed that humans must at one time have ranged across almost the entire island. The most recent date directly associated with Aboriginal activity is 4300 years ago. Since Kangaroo Island was cut off from the mainland perhaps 9000 years ago by the post-glacial rise in sea levels, this raises a suite of questions. Did the occupants leave the island voluntarily? If so, how did they cross the 14.5 km wide Backstairs Passage separating Kangaroo Island from the Fleurieu Peninsula? Alternatively, did the population die out because it was too small to be sustainable, because of some environmental disaster or because of environmental degradation (which may itself have been human-induced)? Or was the island abandoned after the opening of Backstairs Passage and subsequently occupied only sporadically by voyagers from the mainland?

Considerable light would be thrown on these questions if it were possible to establish when Kangaroo Island was depopulated. Did this largely occur at the time the island was separated from the mainland? Was there a surviving population? Or did the island experience intermittent visits from the mainland? If people remained on the island, was the population stable or did it decline gradually or in a stepwise fashion, perhaps in response to environmental forcing?

Kangaroo Island is the only part of the continent in which widespread Aboriginal occupation ended long before the arrival of Europeans. It is thus the one part of Australia where the impact of Aboriginal activity on the natural environment may be assessed by studying the changes that took place after human influence had been removed. Kangaroo Island is also the only part of the continent where European colonisation took place in an unoccupied landscape, one unaffected by recent human disturbance. The island thus represents a natural laboratory in which the role of human activity in altering the natural environment may be assessed.

This project aims first to establish the date of Aboriginal abandonment of Kangaroo Island. This will involve investigating the record of charcoal preserved in lake sediments. The charcoal signal resulting from Aboriginal burning is very different to that produced by natural wildfires, and changes in the magnitude of that signal may provide clues to the intensity of Aboriginal activity on the island.

The second part of the project involves assessing the response of the natural environment to the removal of human activity and, subsequently, to the imposition of European land use practices. This will focus on two key elements of the natural environment: vegetation and soil erosion. The same sedimentary records that retain evidence of fire also preserve information on vegetational change, in the form of fossil pollen grains, and evidence of soil erosion, from sediments washed into the lake from the surrounding catchment.