Postcards from the past: charting the landscape-scale conversion of tropical Australian savanna to closed forest during the 20th century |
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| Authors: | Barry W Brook David M J S Bowman |
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| Institution: | (1) School for Environmental Research, Institute of Advanced Studies, Charles Darwin University, Darwin, NT, 0909, Australia |
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| Abstract: | Repeated sequences of digitised and geo-referenced historical aerial photography provide a powerful means of understanding
landscape change. We use this method to demonstrate a landscape wide expansion of closed forest (42% increase in total coverage)
in the Australian monsoon tropics over the past five decades. Retrospective habitat suitability models (HSI) of closed forest
derived using four landscape measures (drainage distance, slope angle, aspect and elevation) for imagery taken in 1947 correctly
forecast the subsequent spatial distribution of the expansion, with topographic fire protection primarily determining the
closed-forest distribution. The dynamics of the closed forest-savanna boundary were predicted accurately by generalised linear
models, with closed-forest expansion in fire-protected sites along forest edges and regression in the more fire-prone areas.
Two factors may plausibly explain the expansion of closed forests. First, eco-ethnographic records stress the skilful use
of fire by Aboriginal people in protecting isolated and locally resource-rich closed-forest patches. Second, the recent global
increase in atmospheric CO2 may be changing the competitive balance between savanna and forest by enabling C3 trees to grow fast enough to escape the fire trap presented by flammable C4 grasses. |
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| Keywords: | Aerial photography Historical ecology Indigenous fire-use Generalised linear modelling Geographic information systems Landscape ecology Vegetation dynamics |
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