What is a lichen?

Lichen, Opal Creek Ancient Forest Center, Oregon

Copyright Steven Johnson 2013.

Lichens are a common and diverse group of organisms found in the forests of the Northwest. A lichen is an intimate symbiotic relationship between two partners from two different kingdoms of organisms: a fungus and an algae or cyanobacteria. Lichens are slow-growing and generally long-lived. They are known to grow at the fastest one centimeter per year, but often less. The oldest living individual found is about 4,500 years old!

Lichen Physiology

The main vegetative body of lichen, called a thallus, is made up primarily of fungal hyphae, but has a relatively small amount of algae trapped within it. Some lichens have both green algae and cyanobacteria colonies that are able to photosynthesize and create carbohydrates. These colonies of algae produce sugars through photosynthesis that the fungus uses for food, while the fungus produces chemicals that speed photosynthesis and provides protection from ultra-violet radiation.

Hutten pics 1 025Lichens are named and organized taxonomically by the fungal partner because every species is unique in this respect. The algal partner is the same in many different lichens. Fungal reproduction usually happens both sexually and asexually, and lichens are no different. The fungus often reproduces sexually via fungal spores, but the algal partner almost always reproduces asexually. There are some lichen species that only reproduce asexually by means of thallus fragmentation or vegetative propagules; these are dispersal-limited and rare throughout their range, even where the right habitat exists. One such species, the Cascadian endemic old-growth specklebelly (Pseudocyphellaria rainierensis), occurs abundantly in the Opal Creek watershed.

Lichens are able to absorb moisture and nutrients through deposition of water and dust, and are without true roots. They become rapidly hydrated in the slightest precipitation often resulting in a striking color difference between wet and dry specimens.

Indicators of Forest Health

IMG_3437The lichens of Opal Creek are absolutely essential for the health of the forest. They play a vital role in moisture interception and fixation of atmospheric nitrogen. Contrary to popular belief they are not parasitic on trees and instead contribute nutrients to the surrounding plants when they fall to the forest floor. Lichens also provide nesting material for Opal Creek’s myriad of birds and small mammals as well as forage for deer and elk in the winter.

Because lichens are sensitive to air quality disturbance, they serve as bio-indicators of the health of the watersheds in which they exist. Most of the Opal Creek Wilderness contains large amounts of nitrogen-fixing lichens that have very low tolerance for atmospheric pollution, and are an integral component of ancient forests. Oregon lungwort (Lobaria oregana) is a good example of this. Because lichens grow so slowly, late successional communities take a very long time to develop. Because of Opal Creek’s uniquely unfragmented landscape, luxuriant examples of old-growth-obligate species are ubiquitous components of the lichen flora.

Interested in learning more about lichen?

Check out our Mosses, Lichens, and Liverworts workshop taught every other April!

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