Applying a field spectroscopy technique for assessing successional trends of biological soil crusts in a semi-arid environment

We studied the successional stages of biological soil crusts (BSCs) by using in-situ spectroscopic techniques during 6 years of recovery following scraping-sterilization and scraping-crumbling disturbances on north- and south-facing slopes and in plots with and without overland water runoff barriers. Two spectral indices, the Brightness Index (BI) and the Normalized Difference Vegetation Index (NDVI), were used as indicators for evaluating BSC succession, with special attention to differences between the north- and the south-facing slopes. We found that BSC succession could be expressed as linear regressions of the above-mentioned indicators during the experimental years for the different treatments. Both indicators were found to be significantly different in each of the experimental years: BI values decreased while NDVI values increased for each of the three treatments. Thus, the BI can serve as a good indicator during the early years following disturbance while the NDVI can be useful after crusts have become established. We conclude that spectral reflectance measurements of BSCs can be a useful monitoring technique for studying the regeneration of the soil surface without direct disturbance.