Nature's Tiny But Mighty Heroes

By Sydney Prescott

If lichens aren’t mosses, what are they? Lichens are often mistaken for mosses; after all, these two groups grow in similar places, often side by side. Their names only add to the confusion—the term “moss” has been applied to many common names of lichens, such as reindeer moss.

The key difference between the two is that one is a plant, and one is not. Mosses are plants; they have stems and leaves that allow them to photosynthesize. Lichens, on the other hand, are composed of a symbiosis of fungus and photosynthetic algae. The fungus encases the algae, providing structure, protection, and moisture. In return, the algae feed the fungus photosynthesized sugars.

The fungus within lichen can reproduce via spores. However, the algae isn’t included in this reproduction, so the spores need to establish a relationship with an alga or it will die. Scientists aren’t entirely sure how the fungal-algae relationship is formed, but it is theorized that the algae could be transferred via mites or that some algae species can live freely for short amounts of time while they work to locate the fungal part of the lichen. More commonly, lichens reproduce vegetatively, meaning they can grow from a fragment of the parent lichen. They are also dispersed by other animals, such as squirrels or birds that use them in their nests. 

Lichens come in all shapes, sizes, and colors. Some can live for centuries. They are often found as tufts on trees or crusty patches on rock. Inhabiting all areas of the world, from the Arctic to deserts, grasslands, tropical forests, and everything in between, these adaptable creatures have two main resiliency tactics. First, the fungus protects the algae inside from extreme conditions and from drying out. Second, lichens become dormant when growing conditions aren’t favorable. If the environment is too dry, they become brittle, less vibrant, and nearly inactive. When enough moisture comes along, they burst back to life, photosynthesizing and slowly but steadily growing. Lichens can go dormant for years, and have even survived journeys to outer space in dormancy! 

Lichens can grow on just about any surface, natural or human-made. Commonly found on rock, bark, or soil, they are harmless to the surface on which they grow. Birds use them for nesting material, insects camouflage against them, and they are a food source for many animals (although they’re not tasty to humans). Notably, they provide vital nutrition to reindeer and caribou during the long winter months around the North Pole. Covering about 7% of the Earth’s surface, these little organisms play an important role in their ecosystems at a much larger scale than individual relationships. Lichens benefit their environments by cycling carbon, fixing nitrogen, and retaining moisture. As some of the first species to appear on bare rock, lichens colonize environments and make way for soils to form so other species can grow. 

Despite their natural resiliency, lichens are vulnerable to atmospheric pollutants such as heavy metals, carbon, and sulfur. They need clean air to survive. Because of this sensitivity, very few are able to survive in polluted areas such as highways or cities and are thus threatened by urban sprawl and other development. Air pollution causes death in the algal component of lichens, similar to how corals expel their algae due to environmental stress and become bleached. Without the nutrients from photosynthesis, the rest of the lichen will die shortly after. Since each species of lichen has a unique preference for the quality of air in which they grow, they can be used as bioindicators to monitor air quality across America. A bioindicator is a living organism that is used to evaluate the health of the environment. Scientists use the USDA Forest Service National Lichens and Air Quality Database and Clearinghouse to help land managers detect and evaluate trends to assess the impacts of air pollutants. The presence of pollutants in lichen samples is compared to other air quality measurements to determine the health of the surrounding ecosystem. Since lichens are hypersensitive to changes in air quality, they are exceptional indicators of pollution levels. For example, if a sulfur-sensitive species begins to disappear in a region as a sulfur-loving lichen begins to thrive, scientists could infer that an atmospheric spike in sulfur occurred in that region and investigate further. 

Like many species, lichens are also increasingly threatened by climate change. Their ability to survive in diverse and extreme environments means they’ve become specialized to specific regional climates. Recent research in the journal Frontiers in Microbiology suggests that lichens are struggling to cope with rapidly shifting climates. According to Matthew Nelsen, scientist and lead author at the Field Museum of Natural History, “the predicted rate of modern climate change vastly exceeds the rate at which these algae have evolved in the past. This means that certain parts of their range are likely to become inhospitable to them.” The team of scientists found that lichens would need around one million years to adapt to a 1℃ temperature increase, which is less than the predicted rise in global temperatures expected by the end of the century. Rising global temperatures have also contributed to shifting patterns in forest fire frequency and intensity, another factor threatening lichen populations. Lichens are struggling to survive and recolonize after the heat, dryness, and smoke of unprecedentedly severe forest fires. However, lichens aren’t necessarily doomed to extinction. It is possible that some will adapt and others could redistribute to more suitable environments, though these shifts would result in compounding impacts throughout these ecosystems as their range expands. 

Without lichens, food chains would be significantly disrupted, particularly in extreme environments where they are depended upon, such as tundra ecosystems. Biodiversity across the landscape would deplete, impacting the food web more broadly, not to mention the habitat lichens provide for many creatures. Nutrient cycling and air quality would also be altered as these organisms' ability to absorb nutrients and pollutants within the air lessens. However small or unsung lichens may be, their importance is undeniable. Aside from supporting entire ecosystems, not many species get a national database for their biomonitoring abilities. The next time you’re out and about, take a moment to inspect a nearby rock or tree and perhaps you will spot some of these inconspicuous creatures and look upon them with a new appreciation.

Little Field Guide To Lichens

3 Main Categories of Lichen:

Crustose: crust embedded on surfaces such as rocks or tree bark 

Foliose: flat, leaflike lobes that are loosely attached to surfaces

Fruticose: 3D branched or “shrubby” structure

The best time to observe lichens is right after (or during) a rainy period. Lichens will be active, vibrant, and colorful, making them wonderful to behold. They’ll be almost glowing green, yellow, or orange.

In the forest, most lichens will be found on bark/wood. Many different types of lichen can often be found on the same surface.  

Some common species of lichen you may find include monk’s hood lichen, reindeer moss, common greenshield, British soldier lichen, and beard lichen. 

Field tip: If the weather’s been dry, hike with a spray bottle to dampen the lichens you find and watch them come to life! H

Art by Mia Wyant