"Nature Guide Journal"

25 January 2001

One of the most remarkable things in nature, lichens really grab attention in winter. The ample moisture revives the lichens after the dry season, and the die-back of summer's growth makes them more noticeable.

As leaves drop off the deciduous trees, many now-bare branches seem flocked with tufts of faded green. Lichens take many other forms as well: patches of crust; tangles of string; broad or narrow ruffles; spindly clumps that look like bundles of tiny bones or crowds of miniature match sticks or golf tees.

The shapes of lichens may seem so bizarre to our eyes that we may forget they are living things—well, two living things, actually.

A lichen is the result of a symbiotic relationship between a fungus and an alga. The fungus, a many-celled non-green "plant," incorporates many one-celled algae within it's body. The fungus provides structure, nutrients, and some protection for the algae. The algae provide food for the fungus.

Some have said that a lichen is "a fungus that has taken up agriculture."

While either the fungal or algal partner in a lichen can—and often does—survive separately, the partnership allows the combination to prosper under conditions too harsh for either alone. From sun-baked desert rocks to frozen tundra, lichens often thrive were other plants cannot. Lichens even colonize barren sand in wind-protected sites in the Oregon dunes. The adaptive value of this alliance is also witnessed by the fact that about a fifth of the world's fungi may form such partnerships.

Fungus and alga may be bonded at the fungus' earliest stages of development, or the two may bond later. The process of that combination, called "lichenization," is not well understood but apparently occurs in a variety of ways.

The thousand or so different lichens that have been identified in the Pacific Northwest fill important niches in their habitats. Lichens are used by some very small animals (insects, for example) as habitat. Many larger animals, from mice to elk, eat some lichens; birds and small mammals often use lichen as nesting materials. Lichens also fix large amounts of nitrogen from the air and help moderate the humidity around them.

Further, lichens' tolerance for conditions too severe for other plants allows them to pioneer environments, creating a genesis for a progression of successive communities.

Of growing importance to people, various lichens also tend to be quite sensitive to certain air-borne pollutants. Tracking the populations of specific lichens can give a valuable and accurate indication of long-term air quality. Lots of lichens usually means clean air.

And, no, the tufts and masses of lichens adorning twigs, branches, and bark do not hurt the tree. The extraordinary partnership between fungus and alga makes them self-sufficient.

Several lichens in a Coos Bay apple tree in January.