Interactions with the Environment and Us.

Lichens, like many other fungi, provide a means of nutrition for many animals in the forest. It's no surprise that the genus Cladonia is also home to a species of lichen known as the "Reindeer Lichen." At one time, before these were classified as lichens, these organisms were known as Reindeer Moss and Caribou Moss. These are important food sources for Reindeer and Caribou, especially in the more desolate regions of tundra that span the northernmost parts of the world.

In the lower United States, species of deer, turkey, and squirrels often make a meal out of the British Soldiers. They provide a wide range of amino acids as well as minerals to benefit the consuming organism. Local animals that may feast on C. cristatella are included below.

Perhaps more interesting and useful to humans is the fact that lichens can be used as "environmental canaries." If you've ever heard the cliché "Canary in a Coal Mine" you'll know what I mean.

Lichens are environmental canaries in that they alert us to the condition of the environment. Lichens are very susceptible to pollution, more so than other living species. Some hypothesize that this is due to the role of the photobiont in the organism. Since the photobiont must work at optimal efficiency to provide not only for itself, but for the mycobiont, lowered photosynthetic efficiency is not easily tolerated. For example, if Trexoubia erici must expend energy to fix cellular membranes due to environmental poisons, then the mycobinot will suffer. If this becomes continual, lichens will die off and their presence will become less common.

Studies have been performed correlating lichen presence and lung cancer. In regions where pollution levels are minimal enough to allow lichen development, lung cancer levels are considerably lower per capita when compared with higher pollution and lower lichen prevalence areas.

In addition to airborne pollutants, acid rain also has a negative impact on lichen growth. The coal burned in many of the world's power plants releases large amounts of sulfur into the atmosphere. This combines with water and results in a phenomenon called acid rain. The lowest pH ever recorded from acid rain was in Wheeling, WV, where a pH of just under 2.0 was measured. To put this into perspective, the pH of stomach acid in humans ranges from about 1.9 to 2.1. It's not hard to imagine the severe damage that can be caused to any organism, let alone lichens, by something so acidic.

Experiments conducted under laboratory conditions with Cladonia cristatella further help us understand the impact of acid rain. When looking at formazan production (formazan is a pigment produced by Cladonia cristatella), the levels at pH readings of 1.5 and 3.0 remain extremely low, with the pH reading of 1.5 being the worst. A pH of about 5.0 is optimal for these lichens and as the data suggests, formazan pigment levels triple between 3.0 and 5.0.

Depending on the species of lichen, heavy metal pollution may be indicated by lichen growth or absence. In the case of the genus Cladonia, many of the species that fall in this category are surprisingly resistant to many heavy metals. There was one study performed in 2006 that studied the impact of copper on Cladonia cristatella. What researchers found, was that when levels got to high enough, that glutanthione levels declined significantly. Glutanthione linkages occur between the glutamine side chain carboxyl group and the amine group of a cysteine. This chemical plays an important role in lichens due to its ability to reduce hydrogen peroxide and chelate (basically bind up) other heavy metals such as cadmium.

Many things can be learned about environmental health from lichens. Though they may seem like unimportant organisms that grow near fallen trees, their presence or lack thereof can be indicative of overall environmental health in a region.