By LESLIE BISHOP, guest columnist
One of my favorite activities when I was a kid was to take apart a rotting log. I would roll it over to see who was hiding underneath. I might find a salamander or a snake if I was lucky, but I would always find centipedes and beetles. Then I would pull back loose bark to find silken tubes of secretive spiders and telltale trails of sawdust left by termites.
Fortunately, this kid never grew up, and I am still fascinated by what I may find in rotting logs.
The difference now is that I have a better understanding of the process — but I still see beauty. The beauty is that a grand old tree can fall in a wind storm and in its death continue to support life. As soon as the tree hits the forest floor, decomposers begin to break down the wood and recycle the nutrients into the soil. But it is not as easy as it sounds.
Wood is composed of carbohydrates, proteins and lignin. Lignin, along with the carbohydrate cellulose, is responsible for making the cell walls of plants rigid and strong. The only decomposers that can digest cellulose and lignin are bacteria and fungi. When a tree dies, airborne bacteria and fungal spores land on the log and decomposition begins.
Fungi grow inside the log in the form of long strands called hyphae. The tips of the hyphae secrete enzymes that digest the wood so that the fungal cells can absorb nutrients. Mushrooms are the reproductive structures that produce spores. All of the decomposing action of the hyphae is hidden from sight.
Fungi are full of surprises. Two days after the frigid weather we had this year, I found bright orange, fleshy mushrooms growing on a rotting log. These had popped out within one day and pushed their way through a snow cover. If I watch this same log, I am apt to see an entirely new type of mushroom on my next walk.
Yet, this is only a glimpse of the diversity of fungi inside rotting logs. In a recent study, scientists found 398 species of fungi in one log by analyzing fungal DNA from sawdust cores. This diversity is hidden because they all do not create mushrooms at the same time. Different species will appear on the log surface in different stages of decay.
Decomposer animals, such as beetles and termites, are called ecosystem engineers because they create tunnels and chambers in the wood. Their chewing activity and their waste provide more food for the bacteria and fungi already present. When a termite eats wood, it can digest the carbohydrates and proteins, but it cannot digest the lignin and cellulose. But no worries — termites have special bacteria that live in their guts that do the job for them.
The work of the decomposers slowly changes the structure and texture of the log, and through time, creates habitats for thousands of other organisms. Some animals, like salamanders, will hide under the log for protection from extreme heat or cold. Small voles and shrews will nest in hollows, and wood-boring beetles will lay their eggs under bark. Mosses and lichens will grow on the moist surface of a rotting log, and with further decay, ferns and other small plants will grow in the crumbling wood.
Decomposers of various kinds together slowly break down the hard wood of a fallen tree and change it into small pieces. These become the part of the soil and build up nutrient-rich humus. This healthy soil can then nourish a new tree sprout.
Trees give life, even in death.
Leslie Bishop is a Brown County resident and retired biology professor from Earlham College. She can be reached through the newspaper at [email protected].
