Wind speed determines the transition from biocrust-stabilized to active dunes

We examine the hypothesis that above a certain height, crusted, stabilized dunes become non-crusted with a mobile crest. Toward this end, twelve plots, 10 × 10 m, were demarcated along a 1 km-long transect in the Nizzana research site (NRS), western Negev, Israel, extending along a ridge of a dune from the crusted interdune up to a height of 22 m above the interdune, characterized by a non-crusted mobile crest. Within each plot, a 4 × 4 m subplot was established where the upper 3 cm of all surfaces was removed. Surface stability was monitored using six erosion pins from March 2010 to February 2012. In addition, data from a nearby meteorological station were analyzed. The data indicated that drift potential (DP) was the highest during winter and spring. A good correlation (with r2 = 0.73) was found between the monthly DP and the absolute change in pin height. Also, a good correlation (with r2 = 0.85) was found between altitude and the absolute change in pin height. A monthly change in pin height of ∼0.3 cm marked the threshold between the crusted and the non crusted sections of the dune, which corresponds to 8 m above the interdune. The findings imply that as long as the absolute monthly change in pin height is <0.3 cm, crust establishment may take place. The findings point to the capability of the crust to cope with limited surface instability and to the potential of biocrusts to serve as biomarkers for surface stability.