Lichen - The Little Things That Matter

Many different colored lichens cover the side of a rock in Glacier National Park.
Colored lichens blanket the side of a rock at Glacier National Park. Lichens can range in color from black or white to yellow or red, and almost everything in between.

NPS Photo / Tim Rains

When you look out at the forest, you often see the scene from a “big picture” point of view. You probably see the elements which are the most visually appealing or obvious: the trees, boulders, flowers, and animals that call the forest home. But one thing you might not see right away are the different types of lichen that call the forest home, too.

Although lichen may be small, they play an important role in keeping both people and nature healthy. Lichen tell us a lot about the health of the our natural areas—they tell us if the air we’re breathing is clean or not.

Small yellow, white, grey, and black lichen cover a rock at Petrified Forest National Park.
Small yellow, white, grey, and black lichen cover a rock at Petrified Forest National Park. Lichen can grow on many different surfaces, known as substrates, from rocks to trees, and even on cars and buildings.

NPS Photo

What organism is neither plant nor animal, but informs us about the air that we breathe? Lichen!

Lichen are small organisms commonly found throughout the forests of North America. They’re neither plant or animal, but rather they’re organisms unlike any other on Earth. While most people may think lichen are a type of moss, they are actually a combination of an algae and a fungus. The fungus provides a structure for the algae to live in, while the algae provides food for the fungus.

Ranging in size from as small as a penny to strands that can be several feet in length, lichen grow in all types of places. They also range in colors from bright oranges and yellows, to grays and greens, and even black. Lichen are a diverse group of organisms to say the least—as there are more than 3,600 different species of lichen in North America alone!

Different lichen species fill different roles within the ecosystems where they’re found. Lichen are a keystone species in many of the places they call home. A keystone species is an organism that’s vital to the health and well being of an entire ecosystem. Lichen are ecologically important to many national parks, and they have many benefits for nature. The health and survival of many ecosystems is usually linked to certain lichen species.

Here are some of the many benefits that lichen give to nature:

  • They are a keystone species in many ecosystems.

  • They serve as a food source and habitat for many animals such as deer, birds, and rodents.

  • They provide nesting materials for birds.

  • They protect trees and rocks from extreme elements such as rain, wind, and snow.

A student holding a small magnifying glass examines a lichen sample on a rock.
A student examines a lichen sample with a magnifying glass at Joshua Tree National Park.

NPS Photo / Jesmira Bonoan

Heavy Metal Haters - Keeping Our Air Clean

Unlike trees and flowers that get their nutrients from the soil and rain, lichens get the food they need to survive directly from the air. Because lichen rely on the atmosphere for all of their nutrients, they can grow almost anywhere. Since each lichen has a preference for how clean the air needs to be, they can be used as an important tool for measuring air quality.

National Park Service (NPS) and United States Forest Service (USFS) scientists use lichen as a biomonitor to assess air quality across the country. A biomonitor is an important organism that helps indicate the health of the environment as a whole.

Across the United States, NPS and USFS scientists have taken more than 5,000 lichen samples and analyzed them to evaluate air quality. These samples are compared to other air quality measurements, and then used to determine the health of nearby ecosystems.

When the air has too many pollutants in it, such as sulfur, heavy metals (copper or lead), or nitrogen, it can be deadly for lichen. Because lichen are so sensitive to changes in air quality, they serve as an excellent indicator of pollution levels.

Too much sulfur and heavy metals can either kill lichen or slow their growth. On the other hand, certain lichen species thrive with excess atmospheric nitrogen, while other species dislike those conditions. These characteristics are important, and can be used to our advantage when we assess air quality. If nitrogen-loving lichen begin to flourish in a certain area while nitrogen-disliking species begin to disappear, that can tell us about the amount of atmospheric nitrogen in that region.

One of the reasons we don’t want lichen to disappear from the forest is that they also act as an air scrubber for the air that we breathe. Much like a mop cleans a floor, lichen help clean our air. Lichen trap particulate matter in the air like dust, while also absorbing smaller pollutants like sulfur, mercury, and nitrogen. This means cleaner, healthier air for us to breathe.

Cleaner air lowers the risk of respiratory problems like asthma or chronic obstructive pulmonary disease (COPD). Other benefits of clean air include lower risk of respiratory infections, bronchitis, and even premature death.

While they may be smaller in the “big picture,” lichen are integral to keeping both us and our air safe and healthy.

The Big Picture

These tiny organisms play a very important role in the health of parks, and they serve as windows into the world of air. Because they rely on the atmosphere for all their nutrients, they accumulate many different types of elements and particles inside their tissue. When scientists inspect lichen samples, it allows us to peek into the air we breathe on a molecular level, right down to a single element!

So next time you’re in a park and are looking at the “big picture,” think of it like a painting. You see all the prominent parts of the painting, like the trees or the wildlife. But those things wouldn’t be there if it weren’t for the smaller brush strokes - the lichen. The lichen help add detail to the painting and act as the base layers for the whole piece. Every organism needs clean air to breathe at the end of the day, and lichen are critical for telling us if our air is clean and healthy. That’s why we lichen these organisms!

A green, leafy lichen covered with small black spots grows on top of some moss.
The common freckle pelt lichen (Peltigera aphthosa) is one of several lichen species that can grow in an arctic environment. Lichens can grow in a wide variety of places around the world, from the desert to the arctic.

NPS Photo / James Walton

Last updated: May 21, 2018