The lichen in the photo above is like an old friend of mine. I’ve known this lichen since 1972 when I first found it growing on a yellow birch tree in the conifer swamp in the southeast corner of my land. It is called Lobaria pulmonaria after the lobed thallus with its raised network of ridges that resemble lung tissue.
After all the years that the Lobaria has been growing on the bark of the yellow birch it has not gotten very large. Normally, L. pulmonaria grows in on the bark of maple, aspen, beech, ash and other trees with tight bark. But birches have exfoliating bark and as sections of bark peel off they take some of the lichen with them. Thus, it never is able to grow very large on this tree. It is in a good location though, on the north side of the birch in a moist and humid conifer swamp. I check on it at least twice month to be sure it is alright. This is important as it is the only L. pulmonaria on any tree on my property and in the immediate area that I have found. But I haven’t checked every tree either.
Lichens are not plants or even single organisms but symbiotic associations of two or more organisms. The first is a fungi most commonly a species of ascomycetes, the “sac fungi”. Almost half of the 30,000 species of ascomycetes are known to form lichen associations. In a few lichens fungi from the Basidiomycetes (mushrooms) are involved.
The second symbiont in a lichen association is a photosynthetic organism called the “photobiont”. Most often the photobiont is an algae usually from the genus Trebouxia although in Lobaria the green algae is a species of Dictyochloropsis. Other algae genera in lichen associations are Coccomyxa, Stichococcus, and Heteroccus. Prokaryotic cyanobacteria from the genus Nostoc also occur in many lichens.
Lobaria lichens are composed of an ascomycete, a green algae (Dictyochloropsis or Trebouxia), and a cyanobacteria (Nostoc or Scytonema). In L. pulmonaria the photobionts are Dictyochloropsis and Nostoc. Lobaria are indicator species, that is, species with particular ecological tolerances (or intolerances, as the case may be) and so can be used to assess the quality of an area. Healthy growth of Lobaria indicate old forests with high humidity and clean air. Cyanobacteria like Nostoc can fix atmospheric nitrogen. In forests with an abundance of Lobaria and other lichens with cyanobacteria their contribution to the nitrogen budget can be substantial. In one study of L. oregana in old growth Douglas fir forests nitrogen fixation was estimated at 3.15-3.5 kg/ha/year.
L. pulmonaria is not the only lichen growing on the yellow birch tree. There are seven, possibly more, other lichen species. Six of these are Physconia sp., Pyxine sp., Myelochroa auralenta, Heterodermia speciosa, Parmelia rudecta, and Phaeophyscia rubropulchra all so-called foliose lichens.
Brodo, I. M., S. D. Sharnoff, and S. Sharnoff. 2001. Lichens of North America. Yale University Press, New Haven, CT.
Denison, W. C. 1979. Lobaria oregana, a nitrogen-fixing lichen in old-growth Douglas-fir forests. Pages 226-275 in Gordon, J. C., C. T. Wheeler and D. A. Perry., editors. Symbiotic nitrogen fixation in the management of temperate forests. Forest Research Laboratory, Oregon State University, Corvallis, OR.