A new U.S. Forest Service study is the first of its kind to establish how much nitrogen lichens can tolerate -- strongly indicating that the small plant may prove to be a natural barometer for excessive pollution.
One issue of concern for scientists is the finding that important lichen species could be reduced by nearly half in landscapes experiencing relatively mild nitrogen deposits. This study is significant because even though the research was conducted in the Pacific Northwest, lichens grow in many landscapes throughout North America. Findings from the study can help policymakers establish air pollution controls.
“Lichens are very sensitive to pollution and so are useful in evaluating forest health,” said Linda Geiser, a Forest Service scientist. “Their extreme sensitivity to nitrogen makes them valuable as indicator species for monitoring potential harm from human-generated pollutants. The plant may be little but it performs a variety of big ecological functions, such as cycling nutrients.”
Lichens, which are generally greenish in color and are often are mistaken for moss, have a symbiotic union between fungi and algae. They absorb compounds in the air, including pollutants such as nitrogen, which is emitted by vehicles, industrial activities, agriculture and natural processes.
Geiser and her colleagues combined data from a decade worth of lichens surveys and chemical analyses in Oregon and Washington along with Forest Inventory and Analysis data, which cataloged lichen species on all of the public and private forested lands in these areas. From this, they developed a model that depicted the relationship between lichens and nitrogen levels that allowed them to generate numeric pollutant threshold measurements, known as critical loads.
Because the study’s model can be used to predict critical loads in other parts of North America, Geiser and her colleagues are planning to refine a national set of measurement standards. This will let policymakers understand how much nitrogen is acceptable. If Geiser’s team can figure out what level of nitrogen harms the lichens and emissions are kept below that, it should help protect larger ecosystem. The study is featured in the March issue the Forest Service’s Pacific Northwest Region’s publication Science Findings.