Old Man’s Beard Decorates Winter Trees

by Kevin Strauss

The stark whites of winter sometimes make me notice the other colors
around in the forest. One of my favorite northwoods plants, especially visible
in the winter is old man’s beard lichen (Usnea species). This lichen gets it
name from its appearance, since it is made up of stringy light green hairlike
fibers that hang from the branches of dead spruce trees in the woods. The
fibers range in length from 4-10 inches and consisted of a fibrous cord
surrounded by spongy material.

Lichens like old man’s beard are actually made up of two separate organisms:
an algae and a fungus. The algae is the green part of the organism and it
uses photosynthesis to make sugar to feed the lichen. The fungus forms the
structure or body of the organism. While there is some debate about
whether this is a symbiotic partnership or if the fungus is holding the algae
hostage and taking advantage of it.

Since lichens often grow on dead trees, some people thought that lichens
killed the trees, but in reality, the tree was probably dead or almost dead
before the lichen arrived. Lichens spread by spores and if a lichen spore
lands on an area with good sunlight, it will start to grow. Lichens can grow on
the surface of rocks or bare tree branches or shingles if they are remain
undisturbed. Because of this, botanists term them “epiphytes” or “plants
that live on top of other things.” Typically, lichens only use a tree branch as
a perch, unlike the parasitic mistletoe plant that also drains nutrients from a
host plant. Lichens get most their nutrients from the air and rain water,
meaning that they can grow almost anywhere that has clean air, even on
bare rocks.

Scientists believe that lichens were some of the first plants to grow here in
the northcountry when the last of the glaciers retreated 10,000 years ago.
Back then, the landscape consisted of bare rock and gravel. As the lichens
grew and died and decomposed, they formed the soil layer that allowed
grasses and finally trees to colonize the barren land.

The presence of ornate lichens like old man’s beard bode well for air quality,
since these lichens can only grow were there is little or no air pollution. As a
person drives from the northland down Highway 53 and I-35, lichens become
shorter and less common as air pollution increases near urban areas.
So the next time you are out in the woods, keep an eye out for these
pioneering, pollution-monitoring lichens.