Activity Number 3: Surveying a Lichen Transect

Goal: To determine if there is a likelihood of sulphur dioxide, acid rain, fluoride or ozone pollution in your area by surveying lichens along a 1 km transect; to learn transect procedures.

Class Time: 2-3 hours.

Materials
• Log book
• Tree banding material (string, tape)
• Guide to trees, camera and film
• Local map of the area (In the U.S., topographic maps can be obtained easily from your local soil conservation district office.)
• Compass
• Wind sock or streamers
• Graph paper
• Colored pencils
• Plastic laminar and appropriate pen

Background Not all lichens are equally vulnerable to pollution. The fine-threaded fruticose is the most sensitive, foliose less so, while crustose are the least sensitive. For example Usnea articulata, a fruticose lichen of Northern Europe, can be found only where SO² levels are lower than 30 micrograms per cubic meter. Several kinds of crustose, on the other hand, can live in the center of cities without apparent harm, tolerating levels up to 170 micrograms per cubic meter.

A walk around the block at TERC in the city of Cambridge, MA. yielded, for example, a few miserable, miniscule crustose colonies.

This gradient of responsiveness is the basis for many lichen maps of pollution. The presence of high pollutant levels in the air will create a "lichen desert." Moving away from the source of the pollutant, the hardy and simpler crustose lichens are found first (which for our purposes may include the leprose and squamulose types), then the more fragile foliose, and finally, at some distance from the source, the even more delicate fruticose can be seen.

More About the Lichen Transect: Procedure

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