What are biological soil crusts and where do they form?
Biological soil crusts typify many dryland soils and form from the association of soil particles and organic matter with varying proportions of cyanobacteria, algae, lichens and mosses. They have many important functions, including; soil moisture retention, inhibition of weed growth, reduction of wind and water erosion, atmospheric nitrogen fixation and carbon sequestration. A variety of environmental factors influence crust form and distribution at a range of scales. At a continental scale, temperature and rainfall are the greatest influences. At a regional scale, soil type (especially texture) is the predominant control with biological crusts less likely to develop on sandy soils due to their surface mobility. At a localised scale, there appears to be an inverse relationship between biological crust cover and plant cover because they are in direct competition for light and moisture. Shrub canopies can, however, provide protection from disturbance and create shade which can enhance mi
