Heating effects on water repellency in Australian eucalypt forest soils and their value in estimating wildfire soil temperatures
Stefan H. Doerr A H , William H. Blake B , Richard A. Shakesby A C , Frank Stagnitti D , Saskia H. Vuurens E , Geoff S. Humphreys F and Peter Wallbrink GA Department of Geography, University of Wales Swansea, Singleton Park, Swansea SA2 8PP, United Kingdom.
B School of Geography, University of Plymouth, Drake Circus, Plymouth PL4 8AA, United Kingdom. Telephone: +44 (0)1752 233069; fax: +44 (0)1752 233054; email: william.blake@plymouth.ac.uk
C Telephone: +44 (0)1792 2955236; fax: +44 (0)1792 295955; email: R.A.Shakesby@swan.ac.uk
D School of Ecology and Environment, Deakin University, Warrnambool Campus, PO Box 423, Vic. 3280, Australia. Telephone +61 3 5663 3535; fax: + 61 3 556 33143; email: frankst@deakin.edu.au
E Wageningen University, Department of Environmental Science, Nieuwe Kanaal 11, 6709 PA Wageningen, The Netherlands. Telephone: +31 (0) 317 489 111; fax: +31 (0)317 48 39 99;
F Department of Physical Geography, Macquarie University, North Ryde, Sydney, NSW 2109, Australia. Telephone: +61 2 9850 7990; fax: +61 2 9850 8420; email: ghumphre@laurel.ocs.mq.edu.au
G CSIRO Land & Water, GPO Box 1666, Canberra, ACT 2601, Australia. Telephone: +61 2 6246 5823; fax: +61 2 6246 5800; email: Peter.Wallbrink@csiro.au
H Corresponding author. Telephone: +44 1792 295147; fax: +44 1792 295955; email: S.Doerr@swansea.ac.uk
International Journal of Wildland Fire 13(2) 157-163 https://doi.org/10.1071/WF03051
Submitted: 19 June 2003 Accepted: 27 September 2003 Published: 29 June 2004
Abstract
Wildfires can induce or enhance soil water repellency under a range of vegetation communities. According to mainly USA-based laboratory studies, repellency is eliminated at a maximum soil temperature (T) of 280–400°C. Knowledge of T reached during a wildfire is important in evaluating post-fire soil physical properties, fertility and seedbed status. T is, however, notoriously difficult to ascertain retrospectively and often based on indicative observations with a large potential error. Soils under fire-prone Australian eucalypt forests tend to be water repellent when dry or moderately moist even if long unburnt. This study aims to quantify the temperature of water repellency destruction for Australian topsoil material sampled under three sites with contrasting eucalypt cover (Eucalyptus sieberi, E. ovata and E. baxteri). Soil water repellency was present prior to heating in all samples, increased during heating, but was abruptly eliminated at a specific T between 260 and 340°C. Elimination temperature varied somewhat between samples, but was found to be dependent on heating duration, with longest duration resulting in lowest elimination temperature. Results suggest that post-fire water repellency may be used as an aid in hindcasting soil temperature reached during the passage of a fire within repellency-prone environments.
Additional keywords: hydrophobicity; Eucalyptus; Australia; fire intensity; fire severity; soil ecology; soil hydrology.
Acknowledgements
This study was supported by a NERC Research Grant (NER/A/S/2002/00143), the NERC Geophysical Equipment Pool, NERC Advanced Fellowship (NER/J/S/2002/00662) and Australian Research Council International Linkage Scheme Grant LX0211202. Julia Schneider kindly carried out some initial exploratory heating experiments. We are grateful to staff at the Warragamba Catchment Office, Sydney Catchment Authority, and particularly Glen Capararo, for logistical support during sample collection in Nattai National Park. We also thank Rob Bryant of the Department of Chemical Engineering, University of Wales Swansea, for his advice regarding heat transfer processes in soils.
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* To allow for potential experimental error, ± 10°C have been added to the experimentally derived temperatures.
