Wind-Driven Ash Mobilization in Post-Wildfire Mediterranean Forests: Wind Tunnel Insights

Wildfires alter multiple components of forest ecosystems, with post-fire ash forming surface layers that can be mobilised by wind. Although wind erosion is recognised as a relevant post-fire process, the mechanisms controlling ash detachment remain poorly understood. This study examines wind-driven ash detachment using a boundary layer wind tunnel and plate mass loss curves as a direct detachment indicator of ash layers from different forest types. Ash was collected from two sites in mainland Portugal dominated by young maritime pine (YP), mature maritime pine (MP), and eucalyptus (E3), and subjected to two levels of crown consumption (low, LCC; high, HCC). Five ash layer depths (1, 2, 5, 10, 20 mm) were tested for each sample. Results show that thicker layers (5-20 mm) were more easily mobilised at moderate wind speeds (4-6 m∙s -1 ). Eucalyptus ash exhibited the highest resistance to detachment (5.47.2 m∙s -1 ), compared to YP (4.4-5.5 m∙s -1 ) and MP (4.0-5.6 m∙s -1 ). These findings demonstrate clear interactions between ash properties, layer depth, and wind erosion peak-loss velocities, offering new insights into post-wildfire ash detachment and its potential for wind-driven redistribution. • Wind-tunnel experiments quantify post-fire ash detachment from pine and eucalyptus forests. • Thicker ash layers are more easily mobilized at moderate wind speeds. • Eucalyptus ash shows highest resistance to wind erosion compared to young and mature pine ash. • Ash properties, layer depth, and wind speed interact to control post-fire detachment and redistribution.