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Cryptobiotic
Soil Crust
Don't Bust the
Crust!
Biological soil crust is a living groundcover that forms the foundation
of high desert plant life in Canyonlands and the surrounding area.
This knobby, black crust is dominated by cyanobacteria, but also includes
lichens, mosses, green algae,microfungi and bacteria.
Cyanobacteria,
previously called blue-green algae, are one of the oldest known
life forms. It is thought that these organisms were among the firstland
colonizers of the earth's early land masses, and played an integral
role in the formation and stabilization of the earth's early soils.
Extremely thick mats of these organisms converted the earth's original
carbon dioxide-rich atmosphere into one rich in oxygen and capable
of sustaining life.
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Healthy
biological soil crust (NPS Photo by Neal Herbert)
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When
wet, Cyanobacteria move through the soil and bind rock or soil particles,
forming an intricate web of fibers. In this way, loose soil particles
are joined together, and an otherwise unstable surface becomes very
resistant to both wind and water erosion. The soil-binding action
is not dependent on the presence of living filaments. Layers of
abandoned sheaths, built up over long periods of time, can
still be found clinging tenaciously to soil particles, providing
cohesion and stability in sandy soils at depths up to 10cm.
Nitrogen
fixation is another significant capability of cyanobacteria. Vascular
plants are unable to utilize nitrogen as it occurs in the atmosphere.
Cyanobacteria are able to convert atmospheric nitrogen to a form
plants can use. This is especially important in desert ecosystems,
where nitrogen levels are low and often limiting to plant productivity.
Soil crusts
have other functions as well, including an ability to intercept
and store water, nutrients and organic matter that might otherwise
be unavailable to plants.
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Vehicle
tracks damagl crusts (NPS Photo by Neal Herbert)
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Unfortunately,
many human activities negatively affect the presence and health
of soil crusts. Compressional stresses placed on them by footprints
or machinery are extremely harmful, especially when the crusts are
dry and brittle. Tracks in continuous strips, such as those produced
by vehicles or bicycles, create areas that are highly vulnerable
to wind and water erosion. Rainfall carries away loose material,
often creating channels along these tracks, especially on slopes.
Impacted areas
may never fully recover. Under the best circumstances, a thin
veneer of cryptobiotic soil may return in five to seven years. Damage
done to the sheath material, and the accompanying loss of soil nutrients,
is repaired slowly during up to 50 years of cyanobacterial growth.
Lichens and mosses may take even longer to recover.
Avoiding these
fragile crusts is simple. Always drive or ride on designated roads.
Respect road closures and search for places wide enough to pass
other vehicles rather than driving over roadside vegetation. When
hiking, always walk on marked trails, or on other durable surfaces
such as rock or in sandy washes.
Biological
Soil Crust Web Site
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