Monitoring Air Quality with Lichen as a Bioindicator

This post is part of the May Green Moms Carnival, hosted this month by the Green Phone Booth.

Cross-posted at Moms Clean Air Force

Joshua explores plant life outdoors (but not lichen!)

 Lichen, which consists of a symbiotic relationship between a fungus and an alga, is sensitive to atmospheric pollution including nitrogen and sulfur emissions that lead to acid rain, as well as toxic lead and mercury emissions.  This sensitivity makes lichen a valuable biological indicator of air quality.  It can be difficult to identify lichen species, even for seasoned naturalists.  We’ll generalize lichen into three categories for this activity. 

  • Crustose lichens form a “crust” onto their substrate of trees, rocks or soil.  The crust is attached so firmly that it cannot be removed without causing damage.
  • Foliose lichens are leafy (think: foliage) that attach loosely, and the lobes of the leaf are often parallel to the surface of the substrate.
  • Fruticose lichens are the three dimensional, often growing perpendicular to their substrate.  They can look like little bushes growing off the side of a tree or rock.

Look at some pictures of each of these lichens until you’re comfortable identifying them.  (See the resources listed at the end.)

Activity: Go for a nature walk around your yard, a park or other favorite natural environment.  As you walk, stop to look at the types of lichen present.  Lichen is very slow-growing, so try not to disturb it as you examine it to determine if it is crustose, foliose or fruiticose.  Younger children can identify the lichen’s color: bright green, gray-green, blue-green, yellow-green, or even pink! Older children may want to bring a field journal along to diagram the lichen that they see.  Keep track of the number of different types of lichen you see while on your nature walk.  Generally speaking, the more lichen you see (in color and quantity) the cleaner the air.

Analysis: Use the modified Hawskworth-Rose Index below to estimate air quality in the area.

  1. No lichens present – very poor air quality
  2. Crustose lichens only – poor air quality
  3. Crustose and foliose lichens – moderate to good quality (based on number of different lichens)
  4. Fruticose, foliose and crustose lichens – very good air quality

What if we have poor air quality?

If you’re lookin’ for lichen but can’t find it anywhere, you may have very poor air quality.  Please write to your representatives and voice your concerns about your local air.  Children can write letters, take photographs or draw pictures to convey their ideas.  You can also tell the EPA that air quality should be a priority!

What if we have good air quality?

I bet that your representatives would love to hear about that, too! Why not send a letter, drawing or photo to let them know that your air is clean and you want it to stay that way?


  • Track changes in your local lichen each year to see if it increases or decreases.
  • Older children and teens can measure the lichen and calculate its area to collect quantitative data and practice graphing.
  • Photograph the lichen and make a guide to your local species. You don’t have to get technical, you can make up your own names.
  • If you want to get technical, consult an online lichen key to find the scientific names.
  • Grow your own lichen! You can paint on rocks or trees with yogurt to promote lichen growth. Not for those seeking immediate gratification…


Backyard Nature: Lichens


Lichen Lite

How to Know the Lichens

This post is part of my Fun Family Learning series.  Please let me know what you think about it and feel free to request a topic!


Filed under Fun Family Learning, Natural Learning, Nature, Outside, parenting

12 responses to “Monitoring Air Quality with Lichen as a Bioindicator

  1. This is not for me… there is Crustose only on the birch stump in my yard. Liam and I were just looking at it yesterday! Looks like Mama needs to write a letter!

  2. ctdaffodil

    Neat info – I may have to print this out for a cub scout project and use it next fall on our hikes!!

  3. Love this post! I am sending this link on to some people I know who are always trying to remove lichen from every surface 😦


  4. Very informative post! Definitely gives me something to look for on our walks.

  5. This reminds me of a hike I went on with a toddler, who sat down in the middle of the trail a half-mile from the car. I inspired him to keep walking by pointing out the “moss” as I called it on the consecutive trees: “and, look! There’s more moss up here.” He loved touching it. I’ll keep my eyes out for lichen on our walks.

  6. Love how you make the connection between our natural world and how we are negatively impacting it, in a way that kids of all ages (even the grown up ones) can understand and see immediately. As the EPA tries to limited air pollution under the clean air act by setting standard for mercury emissions, big energy companies are fighting against this. For our kids and the lichens, we all need to stand up and voice our support for clean air!

  7. What an interesting way to add some educational fun to our walks. We’ll have to go and check out the lichens. Clean air is a necessity and , as Harriet mentioned, our voices need to be heard demanding clean air.

  8. Love it from one science teacher to another! I need to assess our lichen to see if they are all there. I suspect so, but I’ll need to follow your guide to be sure. I think you’d like my recent book on service learning, I bet you already do it with your students. It’s called Change the World with Service Learning: How to Organize, Lead and Assess Service Learning Projects. Thanks for this informative post!


  9. Dude, you are such a scientist! What cool information. I feel like such a lichen expert now. 🙂


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s