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Using lichen to set air pollution controls

The U.S. Forest Service released a new study showing lichen could help set national air pollution standards based on how much nitrogen the small plant can tolerate:

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 could help policymakers establish air pollution controls.

“Lichens are very sensitive to pollution and so are useful in evaluating forest health,” said Sarah Jovan, 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.

Jovan 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, Jovan and her colleagues are planning to refine a national set of measurement standards. This will let policymakers understand how much nitrogen is acceptable. If Jovan’s team can figure out what level of nitrogen harms the lichens and emissions are kept below that, it could help protect larger ecosystems. The study is featured in the March issue the Forest Service’s Pacific Northwest Region’s publication Science Findings.

The mission of the U.S. Forest Service is to sustain the health, diversity, and productivity of the nation’s forests and grasslands to meet the needs of present and future generations. The agency manages 193 million acres of public land, provides assistance to state and private landowners, and maintains the largest forestry research organization in the world.

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