Aboriginal impacts on fire and vegetation on a Tasmanian island

Aim: To evaluate the influence of climate and Aboriginal landscape management on Holocene vegetation and fire activity.

Location: Flinders Island, Bass Strait, Tasmania where archaeological data document extended periods of human presence and absence over the past 12,000 years.

Methods: We evaluated climate-human-fire interactions through high-resolution pollen, charcoal and geochemical analyses of sediment cores from two wetland sites. Proxies for environmental change are qualitatively compared with archaeological data documenting Aboriginal occupation and later abandonment during the mid-Holocene.

Results: Warm and dry conditions of the early Holocene combined with anthropogenic ignitions promoted frequent fires that sustained highly fire-tolerant Eucalyptus savanna. During the mid-Holocene, when both temperatures and precipitation reached Holocene maxima, archaeological data suggest Aboriginal populations abandoned Flinders Island. At this time, Eucalyptus savanna was replaced by Casuarinaceae and broadleaf forests and fire activity decreased. The late Holocene was marked by a transition to increased incidence of intense fires that was associated with a shift from Casuarinaceae forests to xerophytic scrub dominated by Callitris rhomboidea, a conifer that is sensitive to frequent fires but regenerates well following infrequent fires.

Main conclusions: Palaeoenvironmental analyses from Flinders Island document significant shifts in fire regimes and vegetation types through the Holocene. In the early Holocene, Aboriginal landscape management played a key role in maintaining open Eucalyptus savanna, a prime habitat for marsupial prey species. Increasing aridity and strengthening of the El Niño Southern Oscillation climate mode during the mid to late Holocene contributed to the cessation of permanent human occupation and concomitant reduction of ignitions. Infrequent fire activity led to the dominance of xerophytes, especially Callitris, a genus adapted to drought and infrequent high-severity fires. This study highlights how climate change affects the persistence of human populations on islands and the capacity of human-set fires to create savanna habitats.