Biocrust on soil surface in Utah. Photo George Wuerthner.
Biological soil crusts, known as biocrusts, are lichens, algae, mosses, fungi, and cyanobacteria common on the soil surface.[i]They are critical to arid ecosystems, where they help to reduce soil erosion and maintain stability. They assist in water retention and act like soil mulch. They also create an underground network of filaments that binds soil together.
In arid ecosystems, biocrusts act like living mulch that helps retain moisture in the soil, and they can inhibit the establishment of exotic annuals like cheatgrass. Once biocrusts are destroyed, it is easier to establish annuals such as cheatgrass. [ii]Indeed, the loss of biocrusts is perhaps one of the significant reasons cheatgrass has colonized so much of the West’s sagebrush ecosystems.[iii]
Cheatgrass, a flammable alien annual, invades in areas where biocrusts have been destroyed. Photo George Wuerthner.
Despite their essential role in ecosystem stability, they are easily destroyed by ORVs, mountain bikes, and even hikers. However, the biggest factor in biocrust destruction and loss is livestock, whose hooves break up the crusts.[iv]
One of the adaptations of biocrusts to arid ecosystems is the ability to dry out and suspend respiration without serious consequences.[v]
Another vital function of biocrusts is nitrogen fixation.[vi] Nitrogen is essential to soil fertility.[vii] Soils with biocrusts exhibit higher nitrogen levels than where the biocrusts are absent.[viii]
The micro topography created by soil crusts aids water infiltration.[ix]
Yet the destruction and loss of biocrust get almost no attention from federal and state agencies that manage rangelands. Until cows learn to fly, it is impossible to graze any area without destroying the crusts.
REFERENCES
[i] Roger Rosentreter, 2021 Biological Soil of Crusts of North American Drylands: Cryptic Diversity at Risk https://doi.org/10.1016/B978-0-12-821139-7.00073-8
[ii] Root HT, Miller JED, and Rosentreter R (2020) Grazing disturbance promotes exotic annual grasses by degrading biotic soil crust communities. Ecological Applications 30: e02016.
[iii] Serpe M, Orm JM, Barkes T, and Rosentreter R (2006) Germination and seed water status of four grasses on moss-dominated biological soil crusts from arid lands. Plant Ecology
185: 163–178.
[iv] https://www.thewildlifenews.com/2021/04/06/livestock-influence-on-soil-carbon-storage/
[v] Roger Rosentreter, 2021 Biological Soil of Crusts of North American Drylands: Cryptic Diversity at Risk https://doi.org/10.1016/B978-0-12-821139-7.00073-8
[vi] Belnap J (2002) Nitrogen fixation in biological soil crusts from Southeast Utah, USA. Biology and Fertility of Soils 35: 128–135.
[vii] Dregne HE (1983) Desertification of Arid Lands. New York: Harwood Academic Publishers 1–15.
[viii] Belnap J and Harper KT (1995) Influence of cryptobiotic soil crusts on elemental content of tissue of two desert seed plants. Arid Soil Research and Rehabilitation 9(2): 107–115.
https://doi.org/10.1080/15324989509385879
[ix] Eldridge DJ and Greene RSB (1994) Microbiotic soil crusts: A review of their roles in soil and ecological processes in the rangelands of Australia. Australian Journal of Soil Research
1994(32): 389–415.
