Winter is a time of year that most people tend to think of as very monochromatic – whites and grays, perhaps a bit of blue, and maybe some green from the conifers. And, on the landscape scale, this is probably reasonably accurate. However, when you start poking around, you can turn up some fabulous colours. My mom suggested this as a topic for a post, and so we went out this afternoon to do some hunting.
This photo was taken from the Sugar Maple in my parents’ front yard. It’s an old tree, in the twilight of its life. When I was a kid we had a swing made from a tire hanging from one of its sturdy branches, and a treefort high in the fork of its trunk. It was a healthy tree then, without any blemishes or disease. Since then I’ve watched as some branches have died, leaving gaps in its crown that look like somebody’s taken a quick bite for a midnight snack. The bark started flaking in some spots, and the branch with the swing is long gone. And, perhaps the most obvious sign of a tree in decline, its trunk started blossoming in richly-coloured flora.
Well, not flora, exactly. The growth is actually lichen, which isn’t technically a plant. In fact, it’s not easily classified, because it’s not a single organism, it’s two – a fungus (which is its own type of organism) and an algae (which is a completely different type of organism), partnered together in a symbiotic relationship that benefits both. Although technically the fungus and the algae could live independently, they find it suits them both, especially in harsh or difficult conditions, to partner up so each only has to do half the work. The algae contributes to the partnership by photosynthesizing sugars, much like trees do. It’s the algae that gives lichen its green or blue-green (or sometimes red or brown, depending on the particular type of algae) colour. The fungus, meanwhile, is the house the algae lives in, and it pulls in minerals and nutrients necessary for the pair’s survival.
There are over 25,000 species of lichen in North America alone. Each species is incredibly well-adapted to a particular niche, and they can coexist easily, as you can see in the above photos. Because of the vast number of species, and the superficial similarity of them all to a human eye, I’m not even going to try to classify any of these to any sort of taxonomic level. It is possible, however, to group them into structural categories. In the above photo, the lime green lichen is considered “crustose lichen” – it’s very short and relatively uniform. The blue-gray lichen is a “foliose lichen”, which tend to be as the name suggests – leafy and broader. A third, which does not appear on this tree but is often seen, is “fruticose lichen” – a three-dimensional lichen that resembles tiny branches or shrubs.
Lichen is incredibly hardy, withstanding temperatures and conditions that would see most other plants perish. It can be found in the deserts where temperatures can reach up to 50oC, or in the arctic where it may drop to -50oC. Because of their low profile, they can grow in windy environments that don’t support tall plant life. They can also survive in areas without much soil, because the fungus secretes an acid that roughens the substrate surface (such as a rock face) to allow the attachment of its root-like tendrils. If anywhere epitomizes harsh conditions, it’s Antarctica, and there are over 350 species identified from this continent alone!
They take most of their nutrients and moisture directly from the air. Because of this, lichens are especially sensitive to air pollution. It’s been observed that the more pollution in the air, the fewer species of lichen in an area, to the point where in the city centre there’s practically nothing. In London, England, at the start of the industrial revolution, there was so much pollution in the air from coal-fired plants that the lichen on trees in the city completely died, leaving blackened, soot-covered trunks. A moth that was patterned to camoflauge against the trunk suddenly became very obvious to predators. However, an uncommon dark morph blended in well with the new lichen-free trees, and within a short time nearly all of the moth population were dark. When the air was eventually cleaned up lichen returned to the trees, and the moth reverted to its peppered form. Lichen tends to grow very slowly, at about 1mm per year. Some especially dense patches can be dozens, if not hundreds of years old.
Another old tree in the front yard is a Silver Maple. Although we never played on this tree, it, and its sister a few yards away, have framed the front of the house for decades, and certainly it’s a fixture that I can’t imagine the house without. It must be almost as old as the Sugar Maple, and although it’s retained all of its major branches, the lawn is always littered with small- and medium-sized ones in the spring or after a good storm. Sure enough, when I investigated it had its own patch of lichen along a lot of its lower trunk. There weren’t as many varieties as on the Sugar Maple, I only really noticed two, and one was the same blue-gray type. However, after running off a few shots I peered closer and discovered really, really tiny mushrooms, only 2 or 3mm across, growing amongst the lichen patches!
But that’s a topic for another post. :)