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Destabilisation of coastal dunes after bushfires: a rare occurrence?

Samuel Shumack, Paul Hesse
Macquarie University, Sydney, NSW, Australia

This study tests the commonly stated hypothesis that fire plays a role in destabilising coastal dunes. It is speculated that fire is a disturbance on coastal dunes which may lead to transgression following the reduction of vegetation cover (Hesp 2013; Yizhaq et al. 2013; Rust and Illenberger 2006; Catto 2002). The documented evidence of this process in a coastal setting is limited to scattered charcoal fragments within dunes, possibly associated with times of dune activity (Gaigalas and Padzur 2008; Catto et al. 2002). More often cited in support of this speculation is a body of literature describing activation following fires through the Holocene in sub-arctic pine forested dunes from stratigraphy of well-defined charcoal layers (e.g. Matthews and Seppӓlӓ 2014; Carcaillet et al. 2006; Kӓyhkӧ et al. 1999; Seppӓlӓ 1995; Filion et al. 1991; Filion 1987; Filion1984; Seppӓlӓ 1981). Studies of contemporary post-fire susceptibility to wind erosion are limited to the use of satellite imagery to measure vegetative cover on desert dunes (Levin et al., 2012), and a handful of field surveys (only one of which (Vermeire et al., 2005) was on sand dunes) (Ravi et al., 2012, Stout, 2012, Sankey et al., 2009, Whicker et al., 2006). It appears no appropriate study of the impact of fires on coastal dunes exists. On the other hand, monitoring satellite imagery of coastal dunes in Australia suggests that where dunes are covered by dense fire-adapted vegetation communities, the most common scenario may be a rapid recovery allowing minimal sand movement.
Coastal dunes near Esperance, WA have recently had many hectares burnt in two separate fires on November 21, 2015, and January 4, 2016. Here, large areas of dunes have been active since before the fire, so local conditions clearly allow aeolian activity to persist. The recent fires therefore provide an opportunity to test the role of fire in this process. This study combines climate data analysis with monitoring remote sensing indices of burn severity, vegetation recovery, and dune activity, and with field measurements of vegetation cover, wind profiles and aeolian activity. The aim is to monitor the geomorphic response of the dunes to recent fires and interpret this with regard to a range of potentially influential factors.