Assessing recovery of biological soil crusts across a latitudinal gradient in Western Europe

Biological soil crusts are ecologically important communities in areas where vascular plant coverage is low, and their presence is often vital in prevention of soil erosion. Despite recurrent threats to biological soil crusts across different environments, their recovery after disturbance has been little studied. We therefore established experiments across a latitudinal gradient in Europe, from oland, Sweden in the north, to Gossenheim, Germany and Hochtor, Austria, to Almeria, Spain in the south, spanning over 20 degrees latitude and 2,300 m in altitude, and including natural and semi-natural sites. At each site 10 (1 x 1 m) paired plots were constructed where the biological soil crusts were either completely removed, or left intact. Over a 2-year period (2012-2014) the plots were regularly sampled to assess functional group recovery (cyanobacteria, algae, lichens, bryophytes, vascular plants), soil stability, and chlorophyll, carbon, and nutrient contents. Cyanobacterial assemblages were examined by denaturing gradient gel electrophoresis, a technique used to detect DNA in environmental samples. The results indicated that recovery was site dependent, suggesting that physical and climatic parameters play a major role in biological soil crust recovery. This conclusion is supported by the results of the soil properties, which were found to differ between sites, although they did not show meaningful recovery over the study period. Although 2 years was insufficient for pronounced biological soil crust recovery, this study documents changes over the initial recovery period, suggests management practices for future projects, and recommends proxies for measuring recovery over time.