Seeing air pollution by Candleflame

The Bernard Field Station (abbreviated BFS) is a nature reserve just across the street from Harvey Mudd College, and as a bio major, I’ve toured it many times for various classes. Every time I’m there, I learn something new: how to recognize wild cucumbers, behaviors of fence lizards, the importance of sagebrush to native insect communities, etc. At the beginning of the semester, Prof Donaldson took our class on a brief tour of the field station, and once again, something new caught my eye. 

Many of the California Sagebrush (Artemisia californica), especially ones that looked dry and dead/dormant were covered in this bright yellow stuff (see picture one). The more I thought to look for it, the more I saw it covering dry bark. At the time I thought it was some sort of fungus (which, as you’ll see, is only half right!). In particular, I had heard several times about the parasitic black sooty fungus that covers the leaves of yerba santa (Eriodictyon trichocalyx), and assumed this yellow growth was something similar. Because we were touring the field station as a class, I didn’t have the opportunity or time to look at it in more detail, so I decided to come back and look a little closer another day. 

Picture 1: Yellow bark-dwelling growth

First observation day 

A few weeks later, I returned to the field station to take a closer look. I decided to start small, and just see what information I could gather by looking at a single shrub with this yellow stuff on it. The first thing I noticed was that dotted along the branches alongside the mossy yellow stuff were clusters of something orange growing. Looking briefly around at some of the other shrubs around me, I saw that pretty much every shrub that had the yellow stuff had the orange clumps growing on the bark as well. I took a picture and zoomed in to get a better look at the structure of both. The yellow appeared to be more mossy, whereas the orange growths grew in little indented circles that remind me of red blood cells (see picture 2). 

Because the yellow and orange growths were found together, I wondered if they were in fact the same fungus (I still thought it was just fungus!) in different life cycle stages. 

After I had finished observations, I finally started the task of trying to identify what I was actually looking at. It was incredibly helpful that I knew what plant they were growing on, the California sagebrush. It was only then that I learned that I wasn’t just looking at fungus, but was in fact looking at lichens! 

If you don’t know what a lichen is, I didn’t either before this project, so don’t worry! A lichen is an organism that is made up of two organisms growing symbiotically (meaning mutually beneficially). Lichens are composed of a fungus species and either an algae species, a cyanobacteria species, or both (further reading here ). They’re actually incredibly common! They can grow on bark, rocks, or just in the dirt. I identified the two species I had found using the BFS website as Xanthoria tenax (orange) and Candelaria concolor (yellow), which is commonly known as candleflame lichen for its yellow color. 

Picture 2: Yellow and orange lichen growing on sagebrush bark

Second observation day 

I went to the BFS again to look at more than one shrub at a time to see if I could find patterns in distribution. I found two really interesting things:

1. In areas that have been burned in recent years, I didn’t find any lichens. When exploring one of the areas that was recovering from fire, I couldn’t find yellow lichen, nor did I see much dried out sagebrush. So it was entirely possible that the lichen were not present because their habitat had been destroyed by fire. When I did a little digging into the literature about lichens, I found this study  which noted that lichens do not grow in recently burned areas. 
2. I found two more types of lichen! The first is a white ruffled lichen (see picture 3) that was very abundant on sagebrush, which I’ve identified as Physcia adscendens, again using the BFS website. The second lichen I found was harder to spot because it was black, and I found it only on the bark of a log from a dead tree (see picture 4). For a while I thought this one might just be a mold, like the black sooty mold on yerba santa, but it looked rather similar to the Lecanora munzii lichen listed on the BFS website. 

Pictures 3 and 4: White lichen (left) on sagebrush bark and black lichen (right) on dead tree bark.

I was rather excited about my individual project (which was canceled because of covid), especially my plans to petition to take small samples of lichen to look at under a microscope. Taking a closer look at lichens can sometimes help with species identification. 

As I researched for this project I uncovered a lot more interesting information about my bark-dwelling symbiotic research subjects. Most notably, lichen communities can indicate a lot about the air quality around them. They intake and accumulate heavy metals in the air caused by air pollution, and community composition is heavily influenced by atmospheric nitrogen pollution. Our good friend, the bright yellow Candleflame lichen is one of many lichens that are nitrophytes, meaning they thrive when there’s a lot of nitrogen in the air. The BFS website comments that when Candelaria lichen are the most predominant type of lichen in a community, that’s a good indicator that there is nitrogen air pollution. 
Because the BFS is a nature reserve that is closed to the public, we often like to think of it as ‘untouched’ nature. In a lot of ways, it is in a sense ‘untouched’ - there is no watering and besides the maintenance of the footpaths, the native plants and animals are largely left alone.  But despite the best efforts of the field station, it is influenced by its surroundings and by human activity. Even the most remote part of the field station, distanced from all paths, is exposed to the human-polluted air of Southern California. The bright yellow that covers the BFS warns us that even these ‘preserved’ natural spaces are suffering from human pollution. 

Further Reading:

Papers

1. Knudsen, K,. and J. Kocourková. 2011. Rare Lichen of the Southern California Chaparral. The Chaparralian 8:10-12. https://kennethcapps.com/wp-content/uploads/2018/10/Knudsen1.pdf 
2. Glavich, D. A., and L. H. Geiser. 2008. Potential Approaches to Developing Lichen-Based Critical Loads and Levels for Nitrogen, Sulfur and Metal-Containing Atmospheric Pollutants in North America. The Bryologist 111:638–649. https://www.researchgate.net/publication/232686445_Potential_Approaches_to_Developing_Lichen-Based_Critical_Loads_and_Levels_for_Nitrogen_Sulfur_and_Metal-Containing_Atmospheric_Pollutants_in_North_America 
3. Howarth, R. W. 2008. Coastal nitrogen pollution: A review of sources and trends globally and regionally. Harmful Algae 8:14–20. https://www.sciencedirect.com/science/article/pii/S1568988308001078 

Websites

1. BFS website: http://bfs.claremont.edu/biota/lichens/index.html 
2. More about lichens: https://www.livescience.com/55008-lichens.html 
3. Lichens under the microscope: https://www.britishlichensociety.org.uk/identification/microscope-work 
4. Candleflame lichen: https://www.inaturalist.org/taxa/69430-Candelaria-concolor 

Media Credits:

[1] Photo taken by Matty W. at BFS

[2] Photo taken by Matty W. at BFS

[3] Photo taken by Matty W. at BFS

[4] Photo taken by Matty W. at BFS