Organic soils provide evidence of spatial variation in human-induced vegetation change following European occupation of Tasmania

Aim We test the hypothesis that the European destruction of western Tasmanian Aboriginal society, and consequent changes in burning patterns, resulted in succession towards rain forest near the coast, and an increase in the area of more fire-resistant sedgeland in inland areas.

Location South-western and western Tasmania, Australia.

Methods Attributes of organic soils (surface and underlying dominant horizons) beneath rain forest and sedgeland were described and measured from 559 soil pits in areas with highly siliceous surface geology. Multiple logistic regression was used to discriminate the dominant horizons of rain forest and sedgeland soils. This equation was used to derive scores for all soil pits. The hypothesis that change was greater near existing boundaries was tested using correlation. The hypothesis that change was greater at coastal than inland locations was tested using ANOVA.

Results Both upper horizons of the soils under the fire-sensitive rain forest (¹⁴C-dated to be younger than 60 years) and dominant horizons of these soils had significantly higher organic contents, lower bulk density and more nitrogen than the soils under the fire-requiring sedgeland. Twenty-nine per cent of the soils under sedgeland had dominant horizons that indicated past rain forest. One-quarter of the soils under rain forest had dominant horizons characteristic of sedgeland soils. Although results were heterogeneous in both locations, the former difference was more common inland and the latter near the coast. Change was not higher close to present boundaries.

Main conclusions The characteristics of the dominant horizons and the postcolonial surface horizon give a strong indication of the vegetation that formed them. Changes in fire regimes, caused by the displacement of Tasmanian Aborigines by Europeans, appear to have caused vegetation changes that differed within and between the coast and inland areas. Thus, there has been a strong human role in determining the distributions of vegetation types in the region.