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Journal of the International Association of Wildland Fire
RESEARCH ARTICLE

Frequency and season of fires varies with distance from settlement and grass composition in Eucalyptus miniata savannas of the Darwin region of northern Australia

Louis P. Elliott A C , Donald C. Franklin A and David M. J. S. Bowman A B
+ Author Affiliations
- Author Affiliations

A School for Environmental Research, Charles Darwin University, Darwin, NT 0909, Australia.

B Present address: School of Plant Science, The University of Tasmania, Private Bag 55, Hobart, TAS 7001, Australia.

C Corresponding author. Present address: Weeds Branch, Department of Natural Resources, Environment, the Arts and Sport, PO Box 496, Palmerston, NT 0831, Australia. Email: louis.elliott@nt.gov.au

International Journal of Wildland Fire 18(1) 61-70 https://doi.org/10.1071/WF06158
Submitted: 30 November 2006  Accepted: 24 April 2008   Published: 17 February 2009

Abstract

In savanna environments, fire and grass are inextricably linked by feedback loops. In the Darwin area of northern Australia, flammable tall annual grasses of the genus Sarga (previously Sorghum1) have been implicated in a savanna fire-cycle. We examined the relationship between fire history, the grass layer and distance from settlement using LANDSAT images and plot-based surveys. Areas more than 500 m from settlement were burnt almost twice as often, the additional fires being concentrated late in the dry season and in areas dominated by annual Sarga and even more so where dominated by short annual grasses. Grass cover was a stronger correlate of fire frequency than grass biomass, the two showing a non-linear relationship. Sites dominated by short annual grasses had similar cover to, but markedly lower biomass than those dominated by annual Sarga or perennial grasses. Our results reflect the success of fire suppression in the vicinity of settlements, but little effective management of late dry-season wildfires in remoter areas. We evaluate several hypotheses for the association of frequent fire with annual grasses regardless of their growth form and conclude that fuel connectivity and possibly other fuel characteristics are key issues worthy of further investigation.

Additional keywords: annual grasses, annual Sarga, fire cycle, fire regime, fuel loads, grass biomass, Northern Territory, perennial grasses, tropical savanna.




1 The revision of Sorghum intrans Moench into the Sarga genus by Spangler (2003), while not recognised by the Northern Territory Herbarium, is acknowledged so that readers might be aware that the same plant is being discussed in the present paper. According to this revision, Sarga intrans and Sorghum intrans are equivalent terms. For an earlier reference on Australian Sorghum species see Lazarides et al. (1991).

Acknowledgements

The project was funded by Land and Water Australia (grant NTU07) and an Australian Research Council Linkage Grant (LP0348543) ‘Bushfire smoke and the relationship between human and landscape health’ in partnership with the Northern Territory Government, CSIRO and the Bureau of Meteorology. The Bushfire Council NT and Jeremy Russell-Smith generously provided fire history data and use of a vehicle, and the support of Andrew Edwards, Jeremy Freeman, Mariana Anjos and Ben Lewis with image processing was much appreciated. The enthusiastic assistance of Joana Faria, Cláudia Nogueira, Matt Majid and many others with field work is gratefully acknowledged. Tony Griffiths, Keith McGuinness and Lynda Prior all provided helpful and insightful comments on aspects of the study.


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