Re-evaluating Dust Emission Potential from Burned Surfaces on Vegetated Dunes in the Southwest Kalahari

Sand dunes are not typically considered a major contributor to atmospheric dust loading due to coarse grain sizes and the infrequent observation of dust emission events. In vegetated dune systems, dust emission is less common as plant cover inhibits wind erosion. However, disturbances, such as fire, can rapidly remove protective vegetation cover which exposes resident fine sediments to wind erosion.

This study investigates dust emission potential following fire-induced de-vegetation in the driest region of the world’s largest sand sea, the southwest Kalahari. Adopting a hybrid approach, we combine remote sensing to characterise fire extent and timing and portable wind tunnel (PI-SWERL) experiments to quantify erosion potential.

A 24-year fire inventory reveals that burning is most frequent during or immediately after La Niña events, although anthropogenic land management significantly influences the spatial and temporal distribution of fires. The period for dust emission potential following fire is short, constrained by rapid vegetation recovery typically within 2 years. Grain size analyses indicate that dust-sized particles (<62.5 μm) are present in both burned and unburned dune surfaces; however, no significant depletion of fine particles from burned surfaces was observed, suggesting minimal loss through aeolian processes.

PI-SWERL experiments confirm that these fine particles can be entrained, yet higher threshold friction velocities are required for erosion at burned sites. The presence of biological soil crusts (biocrust) at all burned sites implies a stabilising influence on the erosion threshold. Where the surface had been disturbed, resulting in the removal of the typically present biocrust, our data suggest that dust emission fluxes are, on average, 8-13 times higher than those of unburned surfaces.

These findings indicate that currently there is little potential for dust emission in the post-fire de-vegetation period. This study provides new insights into the mechanisms controlling dust emissions in partially vegetated dune landscapes and highlights the importance of multiple, interacting, surface properties in governing aeolian processes.