Ever since my days in graduate school I have lived in a series of houses that all shared a common feature — a big backyard. I initially liked the idea of space, but very quickly I learned of the joy of putting out nesting boxes for bluebirds, tree swallows or whatever other species might find a nest box interesting. Part of the joy of nest boxes is found in the satisfying process of building them.
In my current yard, I have four different nest boxes that attract a great deal of interest every year. A fifth will go up again this spring after being brought down by heavy snow. Certain boxes have been in service for so many years that the predictable deterioration of raw, untreated pine has forced me to replace parts, if not break them down to harvest the screws and start from scratch.
Last year, I did this with one box that has been the particular favorite of the tree swallows that visit my yard every year. The box had probably been up for 10 years and the whole thing was so rickety that I simply had to replace it outright. I took the box down, headed back to my workshop in the garage and took out all the screws. I absentmindedly placed all of the parts in a neat pile on my workbench and then set about the process of cutting fresh wood to size and assembling the new box.
Well, as luck would have it, I ended up admiring the roof of the old box so much that I couldn’t bear to destroy it. The characteristic that really caught my eye was the gorgeous assemblage of lichens that were growing in such interesting and colorful patterns. I had no idea what species this particular lichen sample might belong to, but my mind reviewed everything I knew about lichens in general.
The most fascinating thing about lichens (pronounced Like-enz) is the fact that they are actually composite organisms that are made up of two very different component species. The first component is an algae which is a single-celled organism called a protist. Many people (including my young self) think of algae as single-celled plants, but it turns out there is no such thing. A plant, by definition, is multi-cellular.
The second half of this chimera is a fungus and, in the case of lichens, it is the fungus that appears to hold the algae something of a hostage. Fungi are interesting in that they grow in a spongy mass of fine threadlike fibers called a hyphae (pronounced Hi-fee). Fungi are heterotrophs, which means they cannot make their own food and must consume the organic compounds of other organisms. Usually this means they behave as parasites on living organisms, or as decomposers on dead organisms.
In lichens, however, the fungi have an entirely different approach. The fungi have trapped photosynthetic algae in their hyphae and they obtain organic compounds like sugars from their prisoners. The algae are so valuable to the fungi that they are kept safe within the “body” of the lichens, and they are provided with minerals and water.
Another amazing feature of these organisms is the fact that the combination of fungus and algae is so tough and resilient. The lid of the birdhouse ended up spending all of last summer on top of my woodpile. Up against the western side of the garage, this area can experience some pretty extreme temperatures under the August sun. Furthermore, the top of the woodpile can become extremely dry when it is baking in the heat, and the lichen will harden up and become quite brittle.
Deprived of water, lichens can live in a type of suspended animation that allows them to endure extremes in heat and then snap out of it as soon at it rains. Add a little rain, however, and the lichen will soak up the water, swell up into a spongy mass and become decorated with some beautiful, vibrant colors.
Lichens are often found growing on rocks and it is extremely interesting to note that in addition to using the rock as a stable substrate for growth, the lichens are also capable of metabolizing the rock itself. Essential minerals are extracted and given to the algae, which in turn provide the fungal portion of the lichen with food. There was a time, back in the distant past, when the entire surface of dry land was nothing more than bare rock, and it is quite likely that lichens played a big role in life’s colonization of the land.
Just before the series of nor’easters hit us, the weather was warm enough for me to retrieve the lichen-encrusted lid of that old nest box and take some photos. Today, the lid is under about a foot of snow on my front porch, but in no time at all the snow will melt and the lichen will resume its quiet life. I shall make it my personal goal to keep this group of lichens safe for as long as the wooden lid they are growing on remains in existence.
Bill Danielson has been a professional writer and nature photographer for 20 years. He has worked for the National Park Service, the U.S. Forest Service and Massachusetts State Parks, and currently teaches high school biology and physics. Visit www.speakingofnature.com for more information, or go to Speaking of Nature on Facebook.