Assessing the geomorphic disturbance from fires on coastal dunes near Esperance, Western Australia: Implications for dune de-stabilisation

摘要

Fire is commonly listed as a contributing disturbance to dune re-activation. This paper aims to characterise post fire disturbance to vegetation and soil surface, and aeolian activity on coastal dunes. Field data were collected in February 2016 at two sites on coastal dunes near Esperance, Western Australia (WA) after recent wildfires in November 2015 and January 2016. We measured wind profiles at burnt and unburnt sites, and assessed recent sand movement, protective covering and burn severity. We also used remote sensing and on-site photos to monitor local patterns of short term biomass recovery. Results suggest that burnt vegetation enables near surface winds to flow with a similar profile shape to bare surfaces. Speed-up ratios (SR) were higher by 5-120% on burnt surfaces when compared with vegetated. However, burnt vegetation did not show the same topographic acceleration as bare dunes. This decelerating effect correlated with surface-level ground cover after removing topographically sheltered data points (r(2) = 0.8, p 0.001). Burnt surfaces had up to 30% more ripples than vegetated sites, but had significantly fewer ripples than previously-bare surfaces (by 60-100%). This was likely due to ground cover (r(2) = 0.95, p 0.001). Effective ground cover appears to be 40%. At one burnt transect a high burn intensity may have inhibited short term germination and re-sprouting. Fire as the sole disturbance is not a major threat to the stability of these dunes, however, extreme burn intensities may leave dunes susceptible to further non-fire disturbance events.