Duration: 30 to 40 minutes
Vocabulary: ecosystem, nutrient, decompose, pest, organic, organism
Summary: Students will explore a fallen log and the different organisms that live there.
Objectives: Students will discover how organic material turns from a living thing into a major component of soil. They will also learn about the habitat a fallen log offers, and the types of organisms that live there.
Materials: magnifying glasses, small collection trays, plastic white spoons, optional: mushroom identification guides
Trees, both living and dead, play an important role in forest ecosystems. There are two different focuses in this activity: one, the conversion of dead trees (and animals) into soil, and two, the ever-changing habitat for creatures big, small, and microscopic that fallen logs offer.
A rotting log passes through ha series of stages as it progresses from tree to soil. During each stage, the log is home to a particular community of plants, animals, and other organisms that consume the log or each other. In doing so, they gradually change the structure of the log, creating a habitat no longer suitable for themselves, but others move in, creating a continuous parade of temporary log dwellers. Those leaving a log seek newer, less decomposed logs to inhabit, while those moving in come from a log that is now too rotten to meet their habitat needs.
Of particular importance are mushrooms, which make the wood soft and allow animals and other organisms to break it down and get inside to either eat the wood or get shelter. As they break it down, burrow, and scrape out material, the pieces of wood get smaller and smaller. Then, as certain organisms like worms and bark beetles eat what is left, they produce castings and frass (feces) that put nutrients in the soil. The smaller pieces of wood that are not eaten provide the loose structure to the soil and its ability to absorb and retain moisture.
Ask students if they have ever looked at a fallen log. What did they find there? Ask students if they would like the insects often found in a fallen log in their houses. Why or why not? Explain that these insects would be called “pests” if they were inside, but should be appreciated and cared for when they are in their natural environment.
Find a fallen log close to school grounds—either along the edge of the property or in an area nearby. Have students get into small groups and give out magnifying glasses, plastic spoons, and collection trays to use to examine the log. Have students gently roll over and investigate the dead log. They can gently pull apart different parts of the log. Collect any small creatures in the collection pans (use white pans in order to see organisms more easily). Try to find mushrooms, worms, salamanders, and bark beetles, as well as anything else living in or under the log. Have students dig into the ground right below the log to try to identify pieces of wood or leaf matter that is contributing to the soil.
Have students draw pictures of the log, soil, and some of the interesting things they found on the log. Get back into groups and have students share their pictures and/or some of the things they found.
Ask students why fallen logs are important. Do they count as a habitat? What kinds of animals live in the log and in the soil?
Why do we try to get rid of ants when they are in our houses but not when they are in the log?
Ask students what they think would happen if dead plants and animals never decomposed. What would the world look like? Would it be a healthy place to live?
Visit the log a few different times throughout the year. How has it changed?