By Maggie Chen
What could be right in front of your eyes and not quite seen? … Lichen! Many people walk past lichen without knowing what they are – which is understandable since they aren’t just one life form but a combination of organisms and no two lichen are the same. As complex life forms, lichen are a symbiotic partnership of two separate organisms: a fungus and an algae. The fungus is the partner that determines the majority of the lichen’s characteristics, which could be the lichen’s thallus shape down to its fruiting bodies. The filaments from the fungus surround and grow into the algal cells and along with determining the lichen’s shape, also provides most of the lichen’s bulk.
Lichen grow on stable and reasonably well-lit surfaces which could include rocks, sides of trees, or even on soil. Lichen could absorb specific mineral nutrients from the substrates that it grows on, but they are overall self-reliant and feed themselves through photosynthesis in their algal cells. This means that lichen that grow on trees are not parasites that feed on the trees any more than how a person would feed on the chair that they sit on. Lichen generally thrive better in drier environments which are areas where they are not often left in standing water. Though, what lichens consider dry may not be what people consider dry. In marshes and cool rainforests, large lichen can be seen hanging from branches of trees giving them the name “old man’s beard.” Lichens provide valuable ecosystem services that include binding and building soil, fixing atmospheric nitrogen, and acting as nesting material for birds. They are also a vital source of food to caribou in the winter (reindeer moss is a lichen!) and are also consumed by flying squirrels, red-backed voles, and a variety of invertebrates.
Lichens are used in a variety of ways by humans too. Lichen have been eaten as food by various cultures across North America, Asia, and Northern Europe (like bread moss, which is a popular edible lichen in Scandinavia). Bryoria and Alectoria are fruticose lichen with strong fibers that can be used to weave cloth. Since prehistoric times, lichen has been used to dress wounds or used as tonics due to their many antibiotic properties.
Along with varying sizes, lichen can vary in color too. Lichen are not just gray crusts but come in rich colors ranging from bright yellow, red, and orange to green, black, brown, silver, and gray. The many colorful chemicals found in lichen can be used as dye to add color to cloth. Lichen grow very slowly but can live for decades or even centuries! While the exact age of a lichen is difficult to pinpoint, the ones that reside on buildings or grow on tombstones can usually be dated using historical photographs or archives. Lichenometry is the dating method that uses lichen growth to determine the age of structures or exposed rocks.
Lichens are also sensitive to atmospheric pollution as they are bio-indicators. Lichens receive the nutrients and water they need from fall out (wet and dry atmospheric deposition) and therefore are sensitive to atmospheric pollution, such as nitrogen. If there is an excess of nitrogen, this would increase the load of nutrients and can harm and kill the algae’s chlorophyll (which is used to produce sugars that feed the alga and fungus). It can be said that lichens are the “canaries in the coal mine” of nitrogen deposition. From observing the changes in lichen species composition and the shifts in lichen health in an area, scientists can start to identify the possible start of ecosystem decline due to excess nitrogen deposition. It is seen that lichen decline in many cities and urban areas across the United States is linked to pollution and habitat modification. In California, atmospheric pollution in the form of smog in combination with the rise in real estate development have been affecting the state’s unique lichen populations. Lichen health can also be affected through other disturbances such as livestock trampling, off-road vehicle recreation, and competition from invasive weeds. Fortunately, lichens are robust and sturdy and are seen to recover when given the chance.
Scientists monitoring lichen health using this bio-monitoring data along with atmospheric deposition data can determine pollution sources and identify detrimental pollution levels in an area too. The importance of collected data from science was seen in the policies put in place. Data collection from the National Park Service (NPS), the National and Atmospheric Deposition Program (NADP), and Environmental Protection Agency (EPA) was used to inform policies that helped us see a decrease in total annual nitrogen deposition from 2002 to 2015. Continued monitoring will help this vital research that aid in protecting sensitive ecosystems and in turn those ecosystem services.
As a complex life form, Lichen varies in shape, size, color based on their alga and fungus pairing. They have many different uses such as acting as a bio-indicator for air quality, some species are consumed by different cultures, some are a food source for animals, their colors can be used as dye for clothes, and much more. Lichens are an example of small parts coming together to make a mighty collective.
Call to Action!
Everyone has the ability to make valuable observations and here is one way you can help! While out on a hike or even walking around your neighborhood at the end of the day, you can submit your lichen observations to inaturalist.org. This information will help scientists and researchers as they study the distribution and potential changes in urban ecosystems and natural environments.
Elias, Scott. (2021). Decline in Mountain Glaciers. Threats to the Artic. Retrieved 8 March, 2023 from https://www.sciencedirect.com/topics/earth-and-planetary-sciences/lichenometry#:~:text=Lichenometry%20is%20a%20geomorphic%20dating,in%20radial%20size%20over%20time.
Fertig, Walter. Ten Things You Might Not Know About Lichens, But Wish You Did. ASU Natural History Collections. Retrieved 8 March, 2023 from
National Atmospheric Deposition Program. (2023). Animated Maps. National Atmospheric Deposition Program. Retrieved 8 March, 2023 from https://nadp.slh.wisc.edu/filelib/maps/animated/N_dep_ani.pdf
National Park Service. (2019). Lichens as Bioindicators. National Park Service. Retrieved 8 March, 2023 from https://www.nps.gov/articles/lichens-as-bioindicators.htm#:~:text=Lichens%20as%20Bio%2DIndicators,increase%20the%20load%20of%20nutrients.
University of California Museum of Paleontology. Lichens: Fossil Record. University of California Berkeley. Retrieved 8 March, 2023 from https://ucmp.berkeley.edu/fungi/lichens/lichenlh.html#:~:text=Lichens%20are%20formed%20from%20a,lichen’s%20physical%20bulk%20and%20shape.
United States Forest Service. (2023). About Lichens. United States Department of Agriculture. Retrieved 8 March, 2023 from https://www.fs.usda.gov/wildflowers/beauty/lichens/about.shtml