What Are Lichens and Why Are They Important?
By Pamela McDormand, NSEN Journalism Volunteer
In this blog post, we are going to look at the basic biology of lichens, their role in old growth forests, what they can tell us about how clean the air is, the carbon capturing they can do, and then finally we will learn about some common and rare lichens here in Nova Scotia.
Basic Lichen Biology
Lichens are a unique and intriguing group of organisms found throughout both wild and urban spaces – from old growth forests to city buildings and structures. These slow-growing assemblages are made up of a fungus and bacterial or algae, working together in a biological partnership that benefits both components.
There are three main types of lichens, which are based on their general shape. Foliose lichens have a leafy appearance, where fruticose lichens are more bushy or even cup-shaped. Crustose lichens form a flat cover or crust over a surface. As the bacteria or algae photosynthesize, they feed the fungus, which protects and houses them.
Ecosystem Roles
Lichens do lots of neat and important things for the communities they are found in:
storing carbon and making nitrogen available
soil structure/ecosystem engineering (maintaining moisture, modulating temperature, insulating against permafrost melt in northern locations, delaying decomposition)
food for grazing mammals like deer
habitat for small invertebrates such as insects
used as dyes and medicines by people
Old Growth Forests
Because some lichens grow very slowly, their presense can tell us something about the age of a forested area. Certain lichens are found almost exclusively in old growth forests. Some researchers have suggested lichens can do an even better job than tree age at indicating which forests should be exempt from harvest activity. In regions with extensive lichen studies, checklists can be used to assess forested areas. Using one of these checklists, which may contain up to several dozen species associated with older, more diverse forest ecosystems, we can determine which areas have been continuously forested for a long time. These lists are tailored to the specific region in which they are to be used, and some species may be tricky to identify. However, once forestry personnel are trained, this method could be much easier than using core samples to age very large trees. Stubble lichens (more formally known as caliciod lichens) are a type of lichen that can provide information about how long an area has been forested and its level of biodiversity. One study here in Nova Scotia considered using just a single coral lichen, Sphaerophorus globosus, measuring its abundance as a function of forest stand age. DNA barcoding techniques may solve some of the issues with identifying lichens species, however, shifts in environmental conditions such as temperature and rainfall could affect lichen distribution, and therefore, any monitoring methods based on them.
Air Quality Indicators
Some lichen species are especially sensitive to pollutants in the air, which means that they can be used to indicate or measure air quality. Lichens do not have roots like vascular plants that can absorb nutrients --- pretty much everything they take in comes from the air and water around them, leaving them “in tune” with whatever atmospheric conditions are present, including pollution levels. There are two main ways to use lichens as air quality monitors. One is through measuring bioaccumulation (where pollutants buildup over time) in the actual tissues and the other is through presence/absence data for specific sensitive species. A lichen species that is more sensitive to pollution is less likely to grow in an area with high levels of contaminants. A wide range of biological processes in lichens may be disturbed when they are exposed to contaminants, including photosynthesis and chlorophyll production, cellular respiration, metabolic processes, protein disruption, cell damage and oxidative stress. Different pollutants will cause different effects, which could provide even more insight into the surrounding air quality.
Carbon Capture and Nutrient Cycling
Along with mosses, lichens make up about a third of land-based carbon reserves. A relatively small amount of biomass is making this substantial contribution to carbon capture, making them incredibly efficient at holding onto carbon. Existing on earth before vascular plants, these organisms often play a role in early successional stages following disturbances. Aiding in the recovery of an ecosystem following a disturbance is one way lichens can help capture carbon, by boosting overall productivity and health. Lichens, mosses and other bryophytes play similar functional roles in ecosystem nutrient cycles. Establishing themselves early and then staying for the long game seems to be their way. Their carbon capture role is aided by their ability to fix nitrogen, which is retained near the surface, rather than underground, as in the case of vascular plants.
Usnea strigosa, also known as bushy beard lichen. Photo: Pamela McDormand (2025).
Parmelia squarrosa, or bottlebrush shield lichen. Photo: Pamela McDormand (2025).
Flavoparmelia caperata, also known as common greenshield. Photo: Pamela McDormand (2025).
Common and Rare Lichens of Nova Scotia
Here in Nova Scotia, we have hundreds of types of lichens. Some you may see frequently on rocks at the park, or on the beach, or even stone buildings. Others are much less common and require very specific growing conditions.
Some common lichens you may see in your neighbourhood include old man’s beard (Usnea longissima), lungwort (Lobaria pulmonaria), yellow scale (Xanthoria parietina), reindeer lichen (Cladonia arbuscula), and shield lichens (Parmelia sp.). The blue felt lichen (Pectenia plumbea) has been named Nova Soctia’s official lichen.
Several species of lichen are currently listed as species at risk in Nova Scotia:
Boreal felt lichen (Erioderma pedicellatum, status: endangered);
Blue felt lichen (status: vulnerable)
Black foam lichen (Anzia colpodes)
Eastern waterfan (Peltigera hydrothyria)
Vole ears (Erioderma mollissimum)
Wrinkled shingle lichen (Pannaria lurida)
Boreal felt lichen is an incredibly rare, endangered lichen. One of the few places it has be found is in the Goldsmith Lake Wilderness Area. Unfortunately, this area is currently being considered for harvest. A group of scientists and concerned citizens spent recent summers camping at this site, surveying the area for biodiversity, including these rare lichens. It remains to be seen if their hard work and dedication will catch the attention of those in charge of deciding which forested areas to harvest, and which ones are in need of protection. Protecting areas where rare lichens grow is vital to the overall health of forested ecosystems and promotes biodiversity.
A magnified (3x) image of Ricasolia quercizans (smooth lungwort), showing cup-sized apothecia. Photo: Pamela McDormand (2025).
Final Remarks
Next time you are out for a walk around your neighbourhood, why not see how many types of lichens you can spot growing on rocks, trees, the sidewalk, or even buildings! The Nova Scotia Museum has published a fantastic guide for anyone interested in exploring lichens in their neighbourhood, which is available here.
References
Cameron, R. and Bondrup-Nielsen, S. (2012) ‘Coral Lichen (Sphaerophorus globosus (Huds. Vain) as an Indicator of Coniferous Old-Growth Forest in Nova Scotia’ Northeastern Naturalist, 19(4) p. 535-540
Conti, M. and Cecchetti, G (2001) ‘Biological monitoring: lichens as bioindicators of air pollution assessment – a review’ Environmental Pollution, 114, p. 471-492
Elbert, W., et al., (2012) ‘Contribution of cryptogamic covers to the global cycles of carbon and nitrogen’ Nature: Geoscience, June 3.
McMullin , T. And Wiersma, Y. (2019) ‘Out with OLD growth, in with the ecological continNEWity: new perspectives on forest conservation’ Frontiers in Ecology and the Environment, 13(3)
Smith, R et al., (2015) ‘A rapid method for landscape assessment of carbon storage and ecosystem function in moss and lichen ground layers’ The Bryologist, 118(1) p. 32-45
Yang, J., et al., (2023) ‘Lichen as Bioindicators: Assessing their Response to Heavy Meatl Pollution in Their Native Ecosystem’ Mycobiology, 51(5) p. 343-353
Additional Resources
Lichens NS: https://www.lichensns.com/
About the Lichen Camp: https://nsforestmatters.ca/the-camps/lichen-camp
Nature Conservancy Canada https://www.natureconservancy.ca/en/what-we-do/resource-centre/featured-species/lichens/boreal-felt-lichen.html
NS Forest notes:
Nova Scotia Museum: https://museum.novascotia.ca/sites/default/files/inline/documents/lichens_infosheet_jan2020.pdf
Nova Scotia Species at Risk https://novascotia.ca/natr/wildlife/species-at-risk/
Also check out this great book:
McMullin, T. and Anderson, F. (2015) Common Lichens of Northeastern North America. New York, The New York Botanical Garden Press.