Growing on Everything but Little Understood: The Strange Ecology of Lichen

Lichens are a close symbiotic relationship between fungi and alga. The fungi species are responsible for most of the lichen’s size and shape, while the alga lives on the surface of the lichen and photosynthesize, providing energy for the entire organism (U.S. Forest Service). Many lichen species are made up of multiple species of alga. About 3,600 species of lichens are native to North America, where they mostly grow on rocks, trees, and soil (U.S. Forest Service). Lichens are also excellent indicators of environmental quality since they absorb air pollutants and provide a record for pollution in an area (Haughland et al., 2018).

The strange biology and diversity of lichens, however, make identifying species particularly difficult. Lichen datasets often contain many errors, including geographical bias and misidentified species. To understand the current state of scientific knowledge on lichen ecology, Haughland et al focused on the fruticose lichen species Cladonia rei in Alberta, Canada. The researchers assessed the distribution and abundance of C. rei, which is difficult to identify and considered very rare. Haughland et al used the Alberta Biodiversity Monitoring Institute (ABMI) as well as historical records of species distributions. By focusing on a single species of lichen, the researchers were able to assess the accuracy of lichen datasets and make suggestions for how they could be improved. 

Haughland et al examined 70,181 lichen specimens and found 27,870 samples in the genus Cladonia, 435 of which were C. rei. They used thin-layer chromatography to test C. rei samples for the presence of homosekikaic acid, a chemical unique to C. rei. Haughland et al also measured native and non-native vascular plant richness and included environmental variables such as soil pH, soil litter, and Alberta natural regions in their logistic regression model. They found that the vast majority of C. rei (93%) grows in upland soils. Abundance was positively correlated with vascular plant richness, soil cover, low disturbance levels, and high latitudes. Geographic bias towards places with high anthropogenic disturbance had led previous studies to conclude that C. rei quite rare. However, C. rei is fairly abundant in undisturbed pastures and grasslands with diverse lichen communities in late stages of succession. Haughland et al also found many errors in the previous identification of Cladonia species.

Haughland et al’s study highlights the complexity of lichen ecology; species have highly specialized niches, live in different environments, and on different surfaces. Lichens are also particularly difficult to identify, especially for novices without access to a lab. The researchers pointed out that many lichenologists don’t have access to labs, although many species cannot be identified without chemical tests. To improve the identification of lichens, they propose standardized methods of sampling to reduce bias and sharing lab resources. 

Although our study was on a much smaller scale, we used ideas from Haughland et al’s paper to make our identification of lichens as accurate as possible. For example, we choose to measure the diameter of the largest lichen in each of 5 cylindrical sections going up the lamppost to document the presence of lichens in an unbiased way. Since we had limited knowledge and tools to identify lichen species, we kept this measure of diversity simple. By observing color and texture, we found 5 main types of lichens, and we documented their presence on each lamppost. Haughland et al’s paper highlighted to the difficulty of identifying lichen species even for experts, so we choose this modified measure of diversity that we could complete with fewer errors. We plan to use these data to understand lichen succession on the lampposts. 

                                                                                    

 

Citations

“About Lichens.” Forest Service Shield, U.S. Forest Service, https://www.fs.fed.us/wildflowers/beauty/lichens/about.shtml. 

Haughland, Diane L., et al. “Tackling Rarity and Sample Bias with Large-Scale Biodiversity   

        Monitoring: A Case Study Examining the Status, Distribution and Ecology of the Lichen 

        Cladonia Rei in Alberta, Canada.” The Lichenologist, vol. 50, no. 2, 2018, pp. 211–230.,     

        https://doi.org/10.1017/s0024282918000099.