Duration: 30 to 40 minutes
Vocabulary: ecosystem, nutrient, decompose, pest, organic, organism, spores, primary excavator, secondary excavator, hyphae, mycelia, frass
Summary: Students will explore a fallen log and the different organisms that live there and in other dead trees.
Objectives: Students will discover how dead trees and fallen logs contribute to the ecosystem, and the variety of organisms that take advantage of the habitat they provide.
Materials: clipboards, pencils, log investigation worksheets, mushroom and salamander ID guides
Many people feel that trees are only valuable when they are alive. It turns out, though, that to support an ecosystem, dead wood is just as valuable as live trees! This is primarily because dead wood provides habitat for many different critters and that dead wood decomposes and releases nutrients back into the ground to then provide for more plants, animals, and habitats.
Once trees die, a variety of organisms take advantage of the new resource. The first are usually bark beetles. These beetles have the power to break through the tough outer bark of the tree, eating it as they go through or burrow in it to make shelter. You can tell a bark beetle has been in a dead tree by looking for burrow tracks or by deposits of beetle frass (poop). Once these beetles create space in the wood mushroom spores can get in and start to grow.
Mushrooms grow by extending their “mycelia” into the wood–white thread-like growths put out by the mushroom to help it reproduce. The mushroom cap we usually see is only reproductive part of the mushroom. The mycelia grow along dead trees and absorb nutrients by secreting enzymes to make the wood soft and to digest it on the outside. Eventually two different mycelia meet and merge and reproduce into the “fruiting bodies”–the mushroom caps. These caps produce spores, which are released into the forest and go on to produce more mushrooms.
One the wood starts to break down, many other insects can start eating the wood and using it as shelter. This includes worms, snails, millipedes, centipedes, psuedoscorpions, spiders, mites, and many others. These insects break down the wood further and make the log into a little city of sorts, where these invertebrates live and feed off each other.
Finally, larger animals make their appearance. Woodpeckers come and peck at the wood to eat the insects inside. Woodpeckers are known as primary excavators, as they create holes in the wood while eating. After that, secondary excavators–animals that move in to use these holes–dig out the wood further to live in. Some secondary excavators include squirrels, possums, raccoons, owls, and more.
Another creature that uses fallen logs is the salamander. Roughly 1/3 of all salamanders in the world live in America, and the majority of those live here in the Appalachian Mountains. Salamanders are amphibians which means that they live part of their life in the water and part on land. As a result, they like to live in moist areas, eating snail, worms, and spiders. For these reasons, logs are ideal homes!
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. Ask students what they might know about an environment if they found a lot of amphibians there.
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 ID guides, fallen log investigation sheets, and clipboards. Have students gently roll over and investigate the dead log. They can gently pull apart different parts of the log. Have students try to find mushrooms, worms, salamanders, and bark beetles, as well as anything else living in or under the log. Have students fill out the worksheet at this time. Get back into groups and have students share their pictures and/or some of the things they found and what they have on their worksheet.
Next, spend time seeing just how many different organisms depend on the dead wood. Spend time looking for as many salamanders and mushrooms as possible, and ID them using the guides. Keep a record of what you find.
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? Should people remove dead logs from their property or forests when they fall?
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?
Have students explore the different ways that dead wood gets taken from forests (considered diseased and a risk, removal for firewood, using for building, etc.) and how they can help stop this.