It was the big new concrete transit center that brought the lichens to town.
In September, a huge new structure opened next to the metro station closest to my office. It has three levels, for buses, more buses, and taxis. It was held up by construction delays and disputes. The county and the transit authority are suing various construction companies for a very large amount of money.
The whole time it was being built, standing partly finished, and being worked on again, the many buses that bring people to and from the station had to stop on the streets nearby. The sidewalks were crowded with bus shelters and passengers. When the transit center was finally opened, the bus shelters eventually went away, leaving bare concrete pads in their place.
Then, one day, in November, something else appeared: trees. Six spindly trees planted along the sidewalk, each about 15 or 20 feet tall, bare of leaves, tied to stakes with lengths of wire, run through garden hose to protect the bark. The first time I saw them, I stopped in my tracks, delighted. It wasn’t the trees; it was the lichens.
Pale, sage-green, dry-looking growths, like ruffly circles of paper, clung to the bark of the first tree, closest to the one remaining bus shelter. I could see the patches dotting the trunks all the way down the block. I didn’t know much about lichen, but I knew that healthy lichen is an indicator of clean air. These trees had obviously been transplanted from somewhere else, in some cushy, relatively clean-aired nursery. “Sorry, lichens.” I thought to myself. In this urban environment, with tall buildings, busy streets, and a LOT of buses, it seemed that their days must be numbered. .
That weekend, I called up Eric Kindahl, a biologist at Hood College in Frederick, Md., who has studied lichens. I wanted to know if I was right about the city being a tough place for lichens–and just to double check what exactly a lichen is.
A lichen, he explained, is a symbiosis—a cooperation between a fungus and an algae or cyanobacteria. The algae or cyanobacteria photosynthesize, like plants, and the fungus lives off the sugars from their symbionts. The fungus and algae don’t take anything from the tree. Any nutrients, like nitrogen or phosphorus, come from the air.
And, it turns out, lichens can grow in cities. “There are some lichens that actually do really well with all of that extra urban pollution that you get,” Kindahl said. Some research suggests that the compounds in air pollution get into the water on the road and splash onto trees; they may have a fertilizing effect. “On campus, if you look at the side of the tree that’s toward the road, they’re covered with lichen.” Some lichens are very sensitive to air pollution. But others are more tolerant.
So lichens can live in the city? “It wouldn’t surprise me, if you’ve got the right kind of substrate and the air quality isn’t too bad,” he said.
The very next morning, I walked my regular route to work. I walked past the trees I’ve walked past every day, between the train tracks and a quiet road. And I noticed something I hadn’t noticed before: Lichens on the trunks. When I got to my building, I realized that the older trees out front, squeezed between a busy sidewalk and a busy road, are also harboring lichens. They are much smaller and subtler than the ones on the young new transplants, but they’re there, fighting it out in the urban environment.
There were lichens right in front of me every day and I never noticed them until I thought to look for it.
Photo: Helen Fields
Part 2 of 2: A meeting with a lichenologist
Part 3 of 2 (oops): Lichen beauty everywhere
The low threshold for fun has served you well. Inspiring urban persistence by you and the lichens!
That explains a lot. When I inherited an ecology course to teach, one of the lab exercises was to show that there was a gradient in lichen abundance along the air pollution gradient provided by the presence of my city. Great idea – only problem was it wasn’t nearly that simple. I threw that exercise out. Maybe if we had been able to identify tolerant species it might have been more interesting.
I had a funny run in with lichen recently in Southern India.
Essentially, I was buying up spices, for myself and as gifts, star anise and all that, and got a bunch of bags from a marketplace one night. But when I got back to my room and saw the bags in the light, I saw that one of them was full of a lichen.
At first I wondered if somebody had effectively sold me grime scraped off a tree and told me it was a spice. But I looked it up. Apparently, using lichen as a spice is a thing! It’s called kalpasi, or black stone flower: https://en.wikipedia.org/wiki/Parmotrema_perlatum
And of course whenever I discover something like this I can’t help but wonder who the person was who first looked at tree fungus and said, “I’m gonna eat that.” But I guess it worked out here.