Structure and function of biological soil crusts

Biological soil crusts are found throughout the world. They are generally d ominated by cyanobacteria, lichens, and mosses. When moistened, cyanobacter ia move through soils, leaving sticky sheaths behind. Sheaths connect loose soil particles, contributing soil resistance to wind and water erosion. Ab andoned sheaths are found up to 10 cm down in soils, providing stability at depth. Moistened sheaths absorb ten times their volume of water. Crusted s urfaces roughened by frostheaving slow rainfall runoff, thus increasing inf iltration. Crusts can reduce germination of exotic annual grasses. They contribute nit rogen to desert ecosystems, where nitrogen often limits productivity. Plant s growing in crusted areas often have higher levels of many nutrients than plants in non-crusted areas. Many land uses are incompatible with crustal integrity. Cyanobacterial fibe rs have little resistance to compressional stress. Crushed crusts contribut e less nitrogen to soils. Impacted soils are susceptible to both wind and w ater erosion, leading to soil loss and burial of nearby crusts. Recovery is generally very slow. Rates depend on climate; size, timing, and intensity of disturbance; and soil type. areas with less stable soils and less rainfall, full recovery may take over 250 years, even with small distu rbances. with more inherent stability or areas with greater rainfall will r ecover more rapidly.