Biological Soil Crusts

Increasingly there is recognition for the importance of soils and soil properties. And on arid and semi-arid rangelands, more attention is being paid to the presence and importance of biological soil crusts.

On rangeland ecosystems, our eyes are often drawn to the obvious: the canopy or lack thereof, the brightly coloured wild flowers, healthy tussocks of bunchgrass and how much forage is available. The charismatic mega-flora gets noticed. But what might we be overlooking?

Biological soil crusts often fill-in the interspaces between bunchgrasses in arid and semi-arid rangelands. They increase site diversity, protect the soil surface from erosive forces and provide nitrogen, an important macronutrient to the soil through biological N fixation.

Biological soil crusts are made up of a broad and complex assemblage of living organisms, including lichens, mosses, liverworts, cyanobacteria, algae, fungi and bacteria. These complex associations grow on and within the uppermost layers of the soil. Due to their small size and obscurity, they remain difficult to identify at a species level. However, increasingly it is recognized that biological soil crusts play vital roles in ecosystem processes and maintaining ecosystem health.

Biological soil crusts can:

  • Act as bio-indicators of environmental stress, including physical stress and buffering of pollutants
  • Stabilize soils, by providing a physical structure over the soil and therein moderating (potential) soil loss
  • Act as an important sink for atmospheric carbon sequestration
  • Support biological nitrogen fixation
  • Be useful as an indicator of ecological health and functioning