What lichens can tell us about climate and pollution

When you walk past a tree in Edmonton's river valley, you may notice tree trunks and branches are covered in multicoloured growths, decorating them in yellow, green, grey and bluish spots. These are lichens. 

Lichens are fungi, not plants. They work closely with their photosynthesizing partner — usually algae — which live inside lichens. 

Lichens are important determinants of air quality, said Troy McMullin, a lichenologist at the Canadian Museum of Nature in Ottawa. 

"You can think of them as little sponges. They get their nutrients and minerals from what is floating by, what's in the air," he said.

"Essentially, they're eating the air and if there's pollutants in the air, they're going to eat those too." 

Different lichens have different sensitivities to pollution and other environmental conditions, such as humidity. 

There are tough and resilient lichens that can withstand some really challenging conditions, and then there are lichens that are more sensitive and require their environment to be more pristine. 

If you know your lichens, you can look for them yourself and learn more about the environmental conditions in your area, McMullin said.

"You'd have to know specific species and you'd have to just go out and look for those," McMullin said. 

Diane Haughland, a lichenologist at the Alberta Biodiversity Monitoring Institute, showed CBC Edmonton several common lichen species you can find in the city. 

Standing at Irene's Lookout on Groat Road on the edge of the steep bank of the river valley, not far from the University of Alberta, she examined tree bark covered in yellow lichens, called hooded sunburst, with a few pale green ones over the tree trunk, called speckled greenshield, and a few practically invisible grey ones — shadow lichens. 

"This, to me, is typical of this dry, exposed location. It's telling us that probably the humidity level is too low for many species that we'll find lower down. But it's also telling us that we don't have terrible air quality right here," she said. 

"If we went into a lichen desert in Edmonton, even these lichens would be extremely, extremely rare across the trees."

In Edmonton, the downtown and industrial areas are considered "lichen deserts," Haughland said.