Trying To Determine Forest Health? Look To The Lichens

6:10 minutes

white and light orange springy looking lichen attached to a tree
Coral lichen on a tree in Newfoundland. This lichen has been demonstrated to usefully discriminate between old-growth and second-growth forests in Nova Scotia, Canada. Credit: Troy McMullin

There aren’t very many old-growth forest left in North America. And while it would be wonderful to be able to preserve all of them, resources to protect those forest patches are also in limited supply. So if you’re forced to choose between two areas of old-growth forest, how do you prioritize which of these islands of biodiversity to focus on?

One of the standard ways to identify significant patches of forest is to look at the size of the trees. But new work published this week in the journal Frontiers in Ecology and the Environment suggests that examining the lichens in a forest plot may give a better picture of the ecological health of an area. Because lichens feed from the air flowing over them, they’re quite sensitive to changes in moisture, nutrients, and pollution, and need long, continuous periods undisturbed.  

Troy McMullin, a research scientist in lichenology at the Canadian Museum of Nature in Ottawa, Ontario, joins Ira to talk about the stories lichens can tell about the forest ecosystem.

Further Reading

Segment Guests

Troy McMullin

Troy McMullin is a research scientist in Lichenology at the Canadian Museum of Nature in Ottawa, Ontario, Canada.

Segment Transcript

IRA FLATOW: For the rest of the hour, let’s head out to the woods. There aren’t that many stands of old growth forest left in North America. And unfortunately, the resources to protect and preserve those forests are limited. So how do you prioritize which of those islands of biodiversity to preserve? 

Well, until now, a standard way to identify the best patches of forest was to look at the size of the trees. Right? Certainly makes sense. But new work published this week in the journal Frontiers in Ecology and the Environment proposes a new way– tilt your head down and look at the lichens. Troy McMullin is a research scientist in lichenology at the Canadian Museum of Nature in Ottawa, Ontario. Welcome to the program. 

TROY MCMULLIN: Hi, Ira. Thanks for having me on. 

IRA FLATOW: Just tell us quickly what a lichen is. 

TROY MCMULLIN: A lichen is actually a fungus that has learned to farm. It’s a standard fungus that’s transformed somewhat to form a greenhouse, where it’s growing algae, and the algae is photosynthesizing and producing carbohydrates and sugars to feed the fungus. 

IRA FLATOW: And what can the lichen tell us when you look at it about the health or diversity of the forest? 

TROY MCMULLIN: Well, lichens have a large gradient of sensitivities to disturbance. So there’s ones that will actually prefer to live in a city, and there’s a whole gradient to those that will only really live in old-growth forests that have been undisturbed for a long period of time. So the ones that we’re proposing to use here are the ones that grow in these really old forests. 

IRA FLATOW: And so you look down at the lichen, and what do you actually look for? What do you see that tells you? 

TROY MCMULLIN: Well you’re looking for the species that would be indicators of these old stands. Or do you mean what do you see when you see a lichen? 

IRA FLATOW: Yeah. When you see– yeah. 

TROY MCMULLIN: Yeah, so lichens come in all shapes and sizes. They’re a lot like a coral reef, in that there are many different colors. There are a lot of really spectacular shapes and sizes. And once you get an eye for them, they tend to get overlooked, because a lot of them are smaller. Not always, but like old man’s beard, the big, stringy, bright, green stuff you see in the West Coast, and the reindeer lichens growing on the ground, the big spiky things. Those are the ones that grow in high abundance that people do notice. 

IRA FLATOW: I’m Ira Flatow. This is Science Friday from WNYC Studios. OK, so you just joined us, talking with Troy McMullin. So if you see lichens, does that tell you that the place is then healthy if you see the lichens going there? 

TROY MCMULLIN: Well, “healthy” is a subjective term. A forest, when it’s young, just has the species that live in young forests. But what we can use lichens for us to tell us that some stands have not been disturbed for a long period of time. and that’s not reflected in the age of the trees. It’s reflected in how long that site has been forested. 

So the trees might only be a few hundred years old, and by every definition that we have for old-growth forests, that would fit them. But the diversity that’s in those stands– that might have accumulated over hundreds or thousands of years, and looking at the trees only as only a proxy for the species that would be there, some stands can have certainly more of this unique biodiversity than others. 

IRA FLATOW: It sounds like this sounds harder than just looking at a patch of forest and saying, hey, the trees here look pretty big, pretty healthy. 

TROY MCMULLIN: Yeah, exactly. A good analogy is looking at a car. You can have two Ford F-150s sitting beside each other that look the exact same, but until you open the hood and climb inside, you don’t really know which one would have the better features. So we’re proposing you get in there and have a look at what species are in there that are really important if you need to– this is to give them a conservation value, so we can identify the forests that we should be targeting more for preservation. 

IRA FLATOW: If I want to go out lichen hunting, or just to do lichen touring, if I can put it like that, how do I tell a lichen from a moss, from a fungus? What do I look for? 

TROY MCMULLIN: That’s a good question. So lichens are generally brighter in color. But if you really want to get into the fine details, you add water. When lichens are dry, they’re hard, and when you add water, they become soft. But if you add water to a moss, or even a fungus– there are fungi that are wet, there’s fungi that are dry, but when you add water, they stay the same. So lichens really have an extreme change. And that’s one easy way of knowing you’ve got a lichen. 

IRA FLATOW: You’re liking your lichen. Sorry. Bad jokes all the time 

TROY MCMULLIN: I always appreciate them, though. 


IRA FLATOW: Good I found a soulmate. So you see a lichen on a big slab of rock. Isn’t it old? I mean, what do you think is the oldest lichen in the world? 

TROY MCMULLIN: They’ve been aged at thousands of years. 

IRA FLATOW: Really? 

TROY MCMULLIN: They’re really slow-growing. So there are some that will grow right into the substrate. They’ll be almost become part of the tree or the rock. And those ones grow extremely slowly, on average less than a millimeter a year. So you’re looking at some patches that are sometimes a foot in diameter– that’s been there a really long time. 

IRA FLATOW: Wow. Are city slickers, we New Yorkers– are we out of luck in looking for lichen? 

TROY MCMULLIN: Well, there’s a few species that actually will like that kind of condition in New York City, so there are species in New York City. But not many of them, and they’re generally very small. And that’s one of the reasons that lichens are an overlooked and understudied group, because you tend to have to get out of the city and into more undisturbed areas to really see the spectacular ones. 

IRA FLATOW: I guess you can go online and find pictures and help in studying the lichens, finding them. 

TROY MCMULLIN: Oh, yeah. Yeah. More and more, there’s field guides to the lichens. 


IRA FLATOW: You can answer the phone, because we’re just about done. Thank you very much for taking the time to be with us. 


IRA FLATOW: You’re welcome. Troy McMullin, research scientist in lichenology– where lichen– do it yourself– at the Canadian Museum of Nature in Ottawa, Ontario.

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