Lichens: Don’t tread on me
Glenwood Springs, CO Colorado
As spring calls us to pull on our hiking boots, it’s important to remember to watch where we walk. Underfoot might be a fragile carpet, a delicate window into a distant past: lichens.
Lichens are a reminder that you are in the presence of an ageless, timeless cycle of ecological succession. They represent the history of an area and its future. As they colonize bare stone over eons of time, they contribute to the soil and biological richness of the region.
Look closely and you will probably see a lichen today. These colorful splashes on rock are some of the oldest living organisms. Lichens are not plants, but are symbionts, composed of a fungus and an algae to create a new species.
They live year-round, growing whenever moisture is available and temperatures are above freezing. Lichens exhibit remarkable ranges of colors: orange, red, green, yellow, black or white as a result of their chemical composition.
Although mostly found on rock, lichens also inhabit bark and soil. They frequently grow on sandstone and granite, and local trees support a bright orange patina of lichen. Lichens can establish colonies on cement and are the constituent of so-called “moss rock.”
Lichens are extremely long-lived, often centuries and up to 10,000 years old. Nearly 14,000 species of lichens occur worldwide, and they inhabit all of Earth’s regions, including arctic and tundra environments. Most of the 600 chemical compounds produced by lichens are unique to lichens and are important in their identification.
Lichens colonize bare rock and have a special role in fixing (making biologically available) nitrogen and carbon essential for plant growth. This is of special importance in arid environments, where soil productivity is low. They can associate with a moss to create cryptogamic soil, with a patterned, almost three-dimensional appearance.
This type of soil lends essential stability to arid lands. In western Colorado, these soil crusts provide up to 70 percent of the living cover and up to 95 percent of the soil biomass between plants. Lichens are indicators of environmental quality and ecosystem health.
To closely observe lichens requires a simple 10X magnification lens. Close-up inspection reveals their unique shapes and growth patterns. Many varieties are relatively flat, appressed to the surface, whereas some have curled or almost leafy forms. Up close, you can pick out “ascomata,” the reproductive stalks, which are usually disk or cup-shaped. You will also be able to distinguish the growth patterns created by the body of the lichen, from its stem (“thallus”) aggregates.
Look closely, but do not touch or displace these life forms. Despite their longevity and adaptability, lichens are fragile. Whether on rock or in cryptogamic soil, lichens are easily crushed by a careless step, and it could take hundreds of years for them to become re-established. If lichens had a slogan, it would be “Don’t tread on me.”
Linda Crockett is an instructional chair at Colorado Mountain College’s Roaring Fork Campus. This material was excerpted from a report she presented in the Natural History of the Desert class.
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