Conducted with the intention of determining the annual progress and severity of pollution in Hamilton’s air-shed, this effective form of biomonitoring is a simple and unique way of gathering data and will be a great aid in tracking the pollution patterns within the city. But what are lichen you ask? Good question!

Although visually similar, lichen are biologically different from mosses. In fact, they are unique in the world of vegetation in that they cannot be neatly classified into any of the ordinary categories we think of as “plants”. The reason is simple: lichen are not a single entity, but a composite of a fungus and a different organism capable of producing food by photosynthesis, like algae. There are close to 14,000 lichen species in the world, all of which differ in size, form, and colour.

Lichen are exposed to air pollutants at all times. Having no deciduous parts (parts that fall off), they are unable to avoid the accumulation of pollutants. And since lichen do not possess roots, their primary source of  needed elements is the air. This means that levels of elements in lichen often reflect the composition of air around them, making them effective biomonitors of atmospheric quality.

Given the variety of species, not all lichen respond identically. Different lichen species have been found to be more sensitive to specific atmospheric pollutants than others. This idea was furthered in the study by McMaster University’s Dr. George Sorger.

Testing both Ash and Maple trees, Sorger found that there existed a relationship between lichen presence (specifically two types: Physcia Millegrana, and Candelaira Colcolor) and Sulphur Dioxide (SO2) and Nitrogen Dioxide (NO2) levels. He found that areas with high SO2 and NO2 had low to non-existent levels of these lichen present, and areas with low levels of SO2 and NO2 had high levels of these lichen present. Given that SO2 and NO2 are good indicators of airborne pollution, we can assume that areas with a high lichen presence have better air quality than those with a low lichen presence. Visual monitoring of these two types of lichen on Maple and Ash trees can give us a better idea of neighbourhood pollution levels.  

So what does the actual monitoring process entail? We want this study be as community inclusive as possible; therefore our methodology is simple and easy to teach and replicate. After first completing a short training session where we cover all the basics, volunteers have been performing the following procedure:

1) Canvass their own neighbourhoods and identify Maple and Ash trees.
2) Once identified, hold up a simple measuring tool (consisting of a frame divided into four quadrants by wire) to the tree trunk, approximately two meters above the ground.
3) Visually inspect the presence of both lichen types in each of the four quadrants and grade their presence on a scale of zero (no lichen) to three (10% covered in lichen).
4) Record their findings and submit them to the GNC for pattern analysis.

Through utilizing this simple yet effective methodology, it is our hope that individuals feel empowered to take a more active leadership role within their communities.  Science does not have to be difficult and left to the professionals. Air quality monitoring is something that any community can champion and utilize. With a bit of knowledge about what to look for and how to see it, and a sense of what the results might mean, individuals anywhere can become informed about the air quality in their area . This is the first step in seeking accountability.

To date, the GNC has held 4 community information/training sessions and numerous others to a variety of school and community groups within the city. Our next community session will be Saturday March 19th, 1:30-3:00pm at the Kenilworth Public Library. We encourage all those aged fifteen and older to get involved!  If you are interested in attending a session, or know of a group who might be interested in participating (community groups, schools, etc), please contact Katie at This e-mail address is being protected from spambots. You need JavaScript enabled to view it .