Trust in the Crust

By Amanda M. Chandler, Greer Lowenstein

Apr 17 2023

earth /ˈərth/
1) the planet on which we live; the world
2) the substance of the land surface; soil

To show our holistic gratitude for planet Earth, we begin with an appreciation of its surface – the basis of all life that subsequently arises from it. The soil on this surface acts as a medium, hosting a myriad of organisms that form intricate webs with one another. These biological soil crusts (referred to by enthusiasts as BSCs, or biocrusts) are mosaics of archaea, microfungi, green algae, lichens, bryophytes, cyanobacteria (aka blue-green algae), and many other microscopic pals.

BSC complexes limit the erosive tendencies of both disturbed and dry earth by aggregating soil particles that might otherwise easily blow or wash away, a service that is especially important in areas negatively impacted by traditional farming and agricultural practices. Some fundamental ways biocrusts promote succession include funneling nitrogen and carbon from their surroundings into the soil, promoting rain accumulation at the soil surface while simultaneously limiting evaporation from beneath the surface, preventing germination of select invasive grasses, and offering shelter for seedlings in an otherwise unforgiving landscape (Belnap and Lange 2002, RMRS 2017, Rosentreter et al. 2007).

In areas of the world where environmental conditions are too extreme to support a rich vascular plant community, lichens and bryophytes primarily affiliated with BSCs are the dominant vegetation. Within the arid and semiarid lands that cover around 40% of the planet’s land surface, plant cover is often sparse or even absent completely (Dettweiler-Robinson et al. 2013). It is not uncommon for these landscapes to be described as “barren”. We’re here to tell you not to believe the hype. In spite of the harsh conditions characterizing these ecosystems, biocrusts constitute up to 70% of dryland ground surfaces. These soil surfaces brim with microbiotic and cryptogamic communities of specialized organisms that thrive in environments with low moisture and high UV exposure (Belnap and Lange 2002, Rosentreter et al. 2007).

Even in more mesic areas of the world, biocrusts fill a critical ecosystem role by altering the soils they inhabit in preparation for the establishment of the vascular plants we know to characterize a given region. They are among the first organisms to begin growth on bare land and their presence makes such areas habitable for the “true” plants (that means flowers and trees, friends!) that successively follow. In other words: no forest may exist without first starting as a “barren” patch of soil pioneered by a BSC community. What appears to most as a desolate dirt patch bereft of life forms is actually teeming with cryptobiotic life, working together to bring in the next contenders for an extreme lifestyle. So, why not trust in that crust? After all, its continual working relationship with the Earth is something we could all take some notes on.

The writing of this story made possible through a National Science Foundation digitization grant (award #2001500). Digitization TCN: Collaborative Research: Building a global consortium of bryophytes and lichens: keystones of cryptobiotic species.


Belnap, J. and O.L. Lange. 2002. Biological Soil Crusts: Structure, Function, and Management. Springer Science & Business Media.

Dettweiler-Robinson, E., J.M. Ponzetti, and J.D. Bakker. 2013. Long-term changes in biological soil crust cover and competition. Ecological Processes 2: 5.

Rocky Mountain Research Station (RMRS). January/February 2017. Don’t bust the biological soil crust: Preserving and restoring an important desert resource. USDA-USFS bulletin, Issue 23.

Rosentreter, R., M. Bowker, and J. Belnap. 2007. A Field Guide to Biological Soil Crusts of Western U.S. Drylands. U.S. Government Printing Office, Denver, Colorado.