Thursday, December 6, 2007

Ask an Usnea

Bushy cord lichen, Usnea subfloridana

Nature abhors a vacuum. It is also not big on pigeonholing. You don’t have to limit yourself to being an animal, plant, or fungus. You could be a combo. You could be a lichen.

Lichens are interesting amalgams of fungi, responsible for their form, and plants, usually algae, whose photosynthetic activities provide the energy to do what lichens do, which includes forming green-grey crusty layers on rocks, flaky patches on tree branches, or, at their most spectacular, clumps of weird green hair dangling from tree limbs.

Lichens are found worldwide and are strongly locked within the food webs of our planet. They are both food and home to mites and other small invertebrates, which are prey to spiders. Slugs and snails also chomp on lichens, and all of the above are prey to shrews and to migratory birds, which in turn are consumed by almost anything larger. Butterflies, moths, stick insects and other insects have evolved to mimic the scraggly appearance of lichens as a defensive tactic, and their larval or adult forms may eat lichen.

Lichens also are important winter food for larger animals, including deer, caribou, and humans. Locally, they are used intensively by the native Douglas' squirrel and rufous hummingbird for nest construction.

About 14,000 lichens are known. There are no doubt many more species unknown, awaiting discovery by intrepid lichenologists, but how many lichenologists can there be on a planet as small as earth? I suspect there are more NHL teams that there are lichenologists.

Lichens lack a root system. They absorb water directly through their surfaces. Some, such as the bushy cord lichen, Usnea subfloridana, can also readily absorb minerals from the air, which makes them important air quality indicators. Absorbed pollutants quickly affect the algal partner. Photosynthesis stops, and the lichen dies. In densely populated areas of the world that have been subjected to decades of air pollution, historically common lichens are long gone.

It is thus reassuring that clumps of Usnea are common in the local bog, which is a bit of a surprise given the planes, trains, and automobiles that swarm it continuously.

Unlike my previous post, in which I described the difficulties in photographing the very elusive Varied Thrush, photographing a lichen is as easy as falling off a log. In fact, I discovered it is very easy to do both, almost simultaneously.

The next time you are out in the woods and come across a patch dotted with lichen, breathe deeply. The air is good. Ask an Usnea.


Cicero Sings said...

We've lots of lichen up here ... and yes we are very privileged to have very clean air. We do breath deeply ... especially before a trip to the coast!

A Local Naturalist said...

I vicariously breathe the very clean air up where you live through the photos from your walks!