The Significance of Lichens

as Bio-indicators

of Air Quality

Background:

Lichens are not organisms themselves; they are the result of a symbiotic relationship between an aerobic fungus and photosynthetic algae (a protist) or cyannobacteria. A similar sort of relationship is probably what led to the creation of eukaryotes. This is called the theory of endosymbiosis and was first described by Lynn Margulis. There are three main kinds of lichens: crustose, foliose, and fruticose. Lichens take in materials from their environment, including air pollution. This contamination bio-accumulates inside the lichen because they are non-vascular. Different lichen have different tolerences to this contamination. Crustose has a high tolerance, foliose a medium tolerance, and fruticose a low tolerance. In other words, fruticose is the most sensitive to air pollution. Similarly, their growth habits have very different morphology. Crustose is almost incorporated into the substrate. Foliose looks leaf-like, hence the name, and fruticose is moss-like in appearance (see Figure 1).

Figure 1: Lichen Growth Forms

Procedure:

To estimate the occurrence (i.e., number of lichen visible) of the various lichen, we used a standardized method of sampling. We laid a transparency over the north, east, south, and west sides of five maple trees at breast height. On this transparency was a grid composed of ten by ten half-inch cells. We sampled maple trees because their relatively smooth bark allows one to easily see all the lichen. We identifed and counted the number of cells covered mostly by lichen to estimate their occurrence.

Results:

(Fig. 2: Graph of Lichens)

Summary:

As seen in figure 2, there was an abundance of crustose, a medium level of foliose, and no fruticose. One can infer from this data that something (i.e., air pollution) hinders the growth of the fruticose, which would explain its absence. This pollution also seems to hinder the growth of foliose. It is quite likely that this contamination comes from the surrounding houses, highways, and businesses. This environmental impact probably does not affect just the lichen population. This hazardous contamination will probably continue to adversely affect the park for years to come.

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