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Charcoal Evidence of the Spatial Extent of the Eucalyptus Woodland Expansions and Rainforest Contractions in North Queensland During the Late Pleistocene

M. S. Hopkins, J. Ash, A. W. Graham, J. Head and R. K. Hewett
Journal of Biogeography
Vol. 20, No. 4 (Jul., 1993), pp. 357-372
Published by: Wiley
DOI: 10.2307/2845585
Stable URL: http://www.jstor.org/stable/2845585
Page Count: 16
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Charcoal Evidence of the Spatial Extent of the Eucalyptus Woodland Expansions and Rainforest Contractions in North Queensland During the Late Pleistocene
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Abstract

Charcoal fragments collected from soil under tropical rainforest in North Queensland indicated that pyrophytic Eucalyptus woodlands occupied substantial areas of all the present humid rainforest massifs between approximately 27,000 BP and 3500 BP. The charcoal collections were carried out in the main massifs of present-day rainforest between latitudes $15^\circ30^\prime S$ and longitudes 145 E and $146^\circ30^\prime E$. All charcoal was collected from locations which precluded the possibility that the charcoal had been transported. Much of the charcoal retained cellular structure, and the taxonomic source was determined using an electron scanning microscope and wood identification keys. All positive identifications belonged to the genus Eucalyptus. Radiocarbon dated samples revealed ages between approximately 27,000 BP and 3500 BP with the majority of samples in the period 13,000-8000 BP. The results provided independent corroboration of, and spatial definition of the areas affected by, the expansion of pyrophytic woodlands dominated by Eucalyptus into rainforest during the late Pleistocene indicated by palynological and sedimentary evidence (Kershaw, 1985, 1989). The evidence suggest Eucalyptus woodlands or forests reached their maximum geographical extent in period 13,000-8000 BP. The decrease in samples data since that time is consistent with the palynological record which indicated fire frequencies decrease and rainforest reinvaded during the Holocene. Changes in palaeoclimates associated with the most recent glaciation provide a plausible explanation for both the Eucalyptus expansion and subsequent rainforest reinvasion. We suggest that the phenomenon, because of its magnitude and recent nature, has exerted a major and continuing effect on the distribution and dynamic of the present rainforest biota. The changes indicate the dynamic nature of tropical landscape forest patterns and the regional vulnerability of rainforest to changes in environment and fire. Both have profound implications for the conservation of tropical forest biodiversity in times of predicted climate change.

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