Pictured Rocks is home to more than 230 species of lichens, including some rare for the Great Lakes region. Visitors can find lichens in almost every lakeshore habitat, from bare ground to open sand plains, on rocky outcrops along waterfalls, in white cedar wetlands, and attached to the bark of many mature trees.
Lichens are hardy and unusual organisms comprised of a fungus and an alga (or photosynthetic bacterium) living together in a symbiotic relationship. The alga converts sunlight to energy through photosynthesis and provides food for the fungus. The fungus provides structure and physical support, and keeps the alga from drying out. This self-contained lifestyle allows lichens to live on just about any substrate and survive under the harshest conditions.
Lichens come in many colors and are grouped into three categories by shape: foliose (leaf-like), fruticose (shrub-like), and crustose (growing closely attached to a surface). The grey colored reindeer lichen, associated with boreal habitats far to the north, is a common crustose lichen that covers the ground in open places throughout the national lakeshore. Other common species here include powderhorn, beard, greenshield, wreath and tube lichens.
Although some species are more shade-tolerant than others, lichens in general favor sunny locations. The appearance of lichens on dead or dying trees leads to the mistaken notion that lichens damage trees or are signs of disease. Lichens are simply taking advantage of the additional light that becomes available in the absence of overhead leaves. Lichen-covered bark may also indicate an older, slower-growing tree, since younger trees shed their bark more often.
Lichens provide food for many wildlife species and nesting material for birds. They are important early colonizers that break down mineral components in rocks and create new soil. Take care not to crush lichens when hiking, as these slow-growing organisms can take many years to recover.
Air Quality Sentinels
Some lichens make excellent air quality bio-indicators as they are particularly sensitive to airborne contaminants. Lichens are so sensitive to sulfur dioxide that it is possible for scientists to calculate the amount of this pollutant in the atmosphere by mapping the occurrence or disappearance of certain lichens in a given area. Researchers have found these particular species here at Pictured Rocks with no signs of damage due to pollution - indicating that air quality in this region is quite good.