You anxiously await the return of spring as a chance to survey winter’s damage to your yard and garden. While walking through your yard after a refreshing spring shower, you suddenly notice a mysterious green growth on your favorite trees. Is it mold, fungus or disease?
Relax, your discovery is probably lichens.
Referred to by many scientists as nature’s pioneers, lichens grow where few other plants can. From backyards to churchyards, tundra to rainforests, lichens establish themselves on rocks, trees, in soil and even man made surfaces such as asphalt and concrete. Their rough surfaces collect wind-blown debris and as they die, their organic matter is added to the mix, playing an important part in soil development. The foundation lichens create paves the way for plants to become established and in turn create more soil.
Lichens are nature’s perfect tenants. A lichen absorbs nothing from its host. Instead it derives water and essential nutrients from the atmosphere.
Lichens are created when a particular fungus partners with particular algae or cyanobacteria [formerly known as blue-green algae] to form an unique organism.
Lichens are a self-sustaining ecosystem. This is called a symbiotic relationship since both plants benefit from this combination. The fungus provides structure, shade and a place to hold water and nutrients for the algae. The algae provides food for both the fungus and itself through photosynthesis.
Specially adapted to withstand extremes of moisture and temperature, lichens become dormant in dry periods, only to come “alive” when moisture is available to them. In favorable conditions the fungus allows more light to get through, triggering the algae to produce food and new tissue.
Although lichens sound complicated, they are classified as lower plants along with mosses, bryophytes, fungus and algae because they do not produce flowers or leaves.
Lichens are divided into three basic forms : crustose, foliose and fruticose.
Crustose lichens are flaky or crust-like and grow flat or often embedded in rocks or tree trunks. Foliose lichens are leaf-like and have a distinctive top and bottom surface. Fruticose lichens are the most delicate and resemble shrubs growing up from the ground or beard-like, similar in shape to Spanish Moss and often seen hanging from trees.
If you have these strange creatures in your yard, consider yourself lucky. Although small in size and easily overlooked, these slow-growing, long-lived plants are a good indication of air quality.
Scientists have been using lichens as bioindicators [living organisms that respond in a clear way to environmental changes] to measure sulfer dioxide, lead and other toxic metals in the air and their effects. Most lichens grow at a rate of less than one millimeter a year and left undisturbed, they can have a lifespan of several centuries.
Lacking the protective cuticle of higher plants, lichens can act like sponges absorbing everything that comes their way, including air pollution. Although most lichens are extremely vulnerable to air pollution, it could take years of absorption before a lichen dies.
As part of a climate change study done at the University of New Hampshire, scientists focused on finding ways to gauge the damage caused by air pollution before the lichens disappear from an area.
Because of their longevity, lichens are like living history books when it comes to estimating the age and change in composition of a forest.
Some types of lichens omly grow on trees over one hundred years old.
Other types disappeared in Pennsylvania along with the American Chestnut and American Elm trees. Noting the changes in lichen flora helps scientists calculate the direction of growth a forest will take if left undisturbed by man.
Besides being bioindicators, lichens association with man goes back to ancient times. Lichens have been used by man for food, clothing, dyes, perfumes and medicines on a global level. Over five hundred unique biochemical compounds are produced by lichens. Although not all lichens are edible, it is estimated that about fifty percent of lichens have
Animals also benefit from the existence of lichens. Lichens are a major food source for grazing animals such as reindeer, elk, moose and caribou when food becomes frozen or scarce. Birds and small mammals use lichens for nesting material, taking advantage of the lichen’s natural insulation properties. They also eat the insects that feed on lichens.
The importance of lichens to other plants goes beyond the creation of soil. Cyanobacteria lichens have the ability to take nitrogen, a major element in plant health, from the air and turn it into usable compounds, contributing to soil fertility.
If you have never heard of lichens, you are not alone. Nature photographers Stephen and Sylvia Sharnoff stated that in over twenty years of photographing lichens they encountered only two people who knew that they were photographing lichens.
From creating soil in a rainforest to feeding reindeer in the tundra, lichens may well be one of nature’s best kept secrets.