It takes about 10 years for a log to rot, for a dead tree to turn into soil. During that time, a rotting log is an ecosystem, complete with a food web of creatures that consume the tree or each other.
While the species of plants and animals present will vary with the stage of decomposition, the roles they play in relation to each other remain constant. There are primary consumers, plants and animals that obtain their nourishment from the log itself. Secondary consumers eat the primary consumers. And the most important group, the scavengers and decomposers, break down the dead remains of both primary and secondary consumers.
The character of the fallen log changes with time. As the moisture content increases, so do the populations of bacteria and fungi, wood-boring insects, and spiders. The outer bark disintegrates quickly and the wood becomes soft and moist, punky. The log becomes a carpet of mosses and lichens.
In late stages of decomposition, earthworms, fungi, and microscopic organisms complete the task of converting wood to soil. In the end, a new tree seedling may germinate on the site of the old log, and one of nature’s cycles is complete.
This activity, designed for children ages 6 to 10, begins with an exploration of a rotting log in nearby woods. Have the children kneel around the log with their eyes closed. Ask them to feel and smell the log. Is it wet or dry? Does it smell like anything they have smelled before? Have them tap the log. Is it hollow or solid?
Using field guides and other resources, show the children pictures of the plants and animals that are found in rotting logs. Primary consumers include fungi and bacteria, bark beetles, click beetles, wood borers, carpenter ants and termites. Likely secondary consumers are centipedes, daddy longlegs, ants, salamanders and even woodpeckers. Scavengers include millipedes, pill bugs, snails, earthworms and slugs.
After exploring a real rotting log, return home to make Soil Soup!
Empty soup cans wrapped in brown construction paper to look like logs (1 per group).
Scraps of paper, construction paper, and cloth.
Markers, colored pencils, or crayons.
Photographs of animals and plants found in rotting logs (field guides, magazines, etc.).
Paper and pencils for writing “recipes.”
Divide the children into small groups of two or three. Give each group one of the wrapped cans and tell them they are going to make soil soup from a rotting log. As the cooks, they will decide which ingredients will be needed to make the soup. For groups of younger children, offer a list of possible ingredients for the soil soup: shade, rain, ice, sun, moss, salamanders, ants, woodpeckers, spiders, mushrooms, etc.
As each ingredient is chosen, add its name or picture to the “rotting log.” Have the field guides and photographs at hand and encourage the children to draw pictures of the ingredients.
When all soups are done, ask each group to describe their ingredients and tell why each was used. Encourage them to place each living ingredient into one of the three groups: primary consumers, secondary consumers, or decomposers.
Older children can also write up their recipes for soil soup. For example: “Take 1 rotting log. Add 3 bark beetles, 2 salamanders, a handful of moss and 2 cups of water. Let it lie for one year…”