This all sounds like scary sci-fi vocabulary: cryptogamic crust, cryptobiotic crust, and microbiotic crust. I like the newest vocabulary word – biological soil crust – because it highlights its life-giving character. These communities – made up of cyanobacteria, green algae, fungi, lichens, mosses, and other tiny organisms – in relationship with soil particles that create a matted crust on top of soil. Think icing on a cake! The crust protects soil from erosion, provides nutrients and water to plants, and shelters plants from drying winds and moderates temperatures. Successful sprouting and growth of native wildflowers likely depends upon these critical ecosystem services provided by functioning biological soil crust.
In our part of Washington, it is easiest to see crusts either in the shrub-steppe or the subalpine. There is no crust when soil gets disturbed and exposed, either from an animal or human’s footprint, a road or trail’s construction, or a landslide. The wind brings the crust colonization by simple and single-celled organisms, that slowly grow. Mosses are often the first colonizers. Fully developed crust may take many many decades or centuries to grow.
Parents and teachers can find excellent text and photo resources geared to help students learn about biological soil crusts. Check out this Resource Card specific to our Columbia Basin’s crust. I like the Arches National Park’s webpage, “Don’t Bust the Crust, It’s Alive!” The U.S. Forest Service’s Rocky Mountain Research Station’s webpage is excellent for all ages. This printable set of mini-flashcards features biological soil crusts, along with dozen’s of other shrub-steppe plants and animals.
For folks who want to delve into technical identification of different types of crusts, downloading and printing a free field identification guide is a good idea. You can view this field guide on the U.S. Geological Service website. Check out to Northwest Lichenologists website to explore ways to learn with experts on field trips or at workshops.
Lichens are one component of biological soil crust. Until recently, biologists defined lichens as a life form that is a symbiotic (required) partnership of two separate simple organisms, a fungus and an algae. The fungus provided the cellular “home” for the food-producing algae. Maybe you remember learning, “Alice algae took a lichen to Freddie fungus and now they live together in a natural relationship. He’s a fun guy.” New research has expanded our thinking beyond binary relationships! This award-winning short film by National Geographic tells the story of recent research conducted at the University of Montana, showing that some lichens consist of more than one species of fungi – a yeast. Also, in some lichens, there are two different photosynthesising single-celled organisms, an algae and a cyanobacteria. Life within the soil is so much more complex that we imagined just a few years ago.
