Clean air is an essential resource for the wellbeing of humans, animals, and ecosystems. Understanding where variations in air quality occur, and what causes these variations (in other words access to clean air vs. exposure to polluted air) can help us to implement more targeted environmental protections and regulations as well as strategies for combating air pollution. Humans' rapid increases in development and expansion of our impact on the Earth have created unintended consequences for the health of the environment. The ecosystems which support the functioning of the planet are at risk of destabilization, but having foresight into how impacts such as environmental pollution and climate change may affect ecosystems is vital to preventing detrimental outcomes and understanding the consequences of our actions. Lichen, an organism formed by a symbiotic relationship between fungi and a photosynthetic algae or cyanobacteria, is highly sensitive to fluctuations in air quality and the environment. Lichen are good bioaccumulators, they absorb and store particulates from their environment such as organic pollutants and heavy metals. This combination of sensitivity and bioaccumulation makes them effective bioindicators and an ideal candidate for sampling and identifying the sources and extent of environmental harm.
A range of prior studies have used lichen as a bioindicator. Studies utilize lichen in locations in which it naturally occurs, including both urban and rural settings, as well as through transplants placed with the intention of analyzing samples to assess various environmental metrics. I synthesized dozens of these studies, supplemented by interpretation of data collected by the United States Forest Service (USFS) on lichen as an indicator of air quality. This analysis explores how lichen can be used as a bioindicator, identifies trends and key takeaways in existing research, and analyzes the data to understand what it can tell us about the health of the environment, ecosystems, and lichen on an organismal level.