This piece was cross-posted at Farmer’s Daughter.
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.
- No lichens present – very poor air quality
- Crustose lichens only – poor air quality
- Crustose and foliose lichens – moderate to good quality (based on number of different lichens)
- 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…