It was a splash of colour in a snow-blanketed forestscape. There, by the flowing dark waters of the west branch of the Bear River stood a massive old spruce, adorned not so much by snow, but by a raiment of brilliant sage-green “old man’s beard” lichen. This one tree shone bright in the monochromatic landscape. It was testament to the hardiness and beauty of lichens.
Atlantic Canada is extremely rich in these unique “plants” (although they’re not actually plants at all, it’s a convenient moniker). The approximately 1,000 species found in the region grow in virtually every terrestrial habitat and ecosystem, from the islands along the Atlantic coast of Nova Scotia to the farthest reaches of northern Labrador. Beyond that, the planet’s 20,000 species of lichens have been found living in some of the most hostile places on Earth, including hundreds of species in Antarctica. Some estimates say they cover up to eight per cent of the Earth’s land mass. Maybe it’s not so surprising they thrive in so many places when you consider they’ve had 400 million years to evolve and adapt to virtually any environment.
The true nature of these vital members of so many ecosystems was only discovered in 1867 by Swiss botanist Simon Schwendener. He learned something about them that was revolutionary at the time: they are actually a biological marriage of two separate kingdoms of life, fungi and algae, living as a single organism. It was one of the first discoveries of the process of symbiosis, a relationship where two or more species “join” together to form a mutually beneficial relationship. In lichens, cells of green algae live enfolded within a weave of nearly microscopic fungi filaments, creating a true living partnership. In some species, the fungus is paired with a photosynthetic cyanobacteria rather than a green alga, and recent studies have indicated that a few species of lichen contain both green algae and cyanobacteria.
Three ancient forms of life—a mushroom, some moss, and few Cladonia-type lichens—share a little space in the forest.
Green algae and cyanobacteria produce carbohydrates (sugars) by using photosynthesis to utilize the energy of sunlight. These sugars provide essential nutrients to the fungi. To return the favour, the fungi provides water and mineral nutrients taken from the environment, as well as protection from the elements and a surface structure for the algae to anchor to. Some have said that a lichen is a fungus that has learned to farm algae!
Like proverbial canaries in a coalmine, lichens are some of the Earth’s most effective bioindicators. Since they get most of what they need directly from the air, they are particularly good at telling us how clean that air is. Not all are equally good in this regard, however. Some crusty lichens like hammered shield are much more tolerant of pollution than others. That’s why we can often see them growing on old gravestones, masonry or tree bark, even in busy urban areas. Many leafy species, such as lung lichens (lungworts), are extremely sensitive to pollutants and are much less common in cities. Toxins in the air can destroy the chlorophyll they need for photosynthesis in the production of sugars.
In fact, too much sulphur dioxide or nitrogen, both of which are produced by the burning of fossil fuels and other industrial processes, will kill them. Therefore, an absence of such lichens or their decline in habitats where they would normally thrive (such as in coastal forests) can raise a flag that an ecosystem’s overall health may be compromised by pollution. So, if the lichens aren’t flourishing, there’s a good chance the forests they live in are declining. On the other hand, healthy and abundant lichens indicate good, clean air. Recently, the discovery of a continued decline of lichen populations in Nova Scotia has caused concerns about the overall health of the province’s forests.
Despite their ancient legacy and adaptability, about 600 of the world’s 20,000 lichens are threatened with extinction. Nova Scotia alone has four species on its endangered species list. One of them, boreal felt lichen, is among the most imperiled lichens on Earth, with just a handful of individuals remaining in the province and a somewhat larger population in Newfoundland. It hasn’t been seen since the early 20th century in New Brunswick.
In our day-to-day world it’s easy to overlook lichens, their subtle beauty and their crucial role in ecosystems. They are an irreplaceable element of the Earth’s living community and deserve our attention