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Engage:
Write the following statement on the board, or project, as a “do now” or “warm up” activity:
“The emerald ash borer, an invasive insect from Asia, has already been discovered in some parts of Minneapolis, MN, and the city has decided to cut down all 38,000 ash trees on public property. This includes trees in urban parks, small urban forests, and on city streets. If they aren’t cut down, they will be killed by the insect and can fall onto buildings, cars, or pedestrians. Explain at least two consequences for cutting down all of the ash trees in Minneapolis, MN.”
Students may focus on simple consequences such as: less oxygen, less shade, less leaf litter to clean up in the fall, etc. Make a list on the board of all of the consequences, paying attention to whether students are thinking about the ecological function of the ash tree. Then, ask students: “What would you need to know in order to understand all of the ecological consequences for cutting down the ash trees in Minneapolis?” Hopefully, students will mention needing to know:
Based on this conversation, students should have generated a range of possible ways in which trees affect the environment around them. In the next activity, they will gain more insight into how changing a forest’s composition may affect the ecosystem.
Explore:
Ask students to think back to the first lesson, and to find their data for their schoolyard plots. Project, or create on the board, a graph of the numbers of trees of all species found. Then, divide students into small groups. Each small group receives an envelope that contains a specific “scenario”. You will need to write in which is your most common tree for #2 and the most “valuable” tree for #4. Valuable can be defined as a tree that provides specific ecosystem services such as supporting a specific herbivore, sequestering carbon, etc. You may have to have repeats of each group in a larger class. These are provided as cards on the last page of this lesson plan.
Students should complete the attached handout as they have their discussion in their small group, and then take notes as other groups share their answers.
Explain:
Student groups should share their answers while everyone takes notes on their graphic organizer. Ask students to respectfully ask questions and challenge the assumptions made by each group. As students are presenting, keep track of the answers on the board (or Smartboard) and make sure that an appropriate discussion takes place about the types of changes that students are hypothesizing. Students should focus on what they learned about in their focus lesson – for example, if they learned about how decomposition varies between maples and oaks, they should explain how losing all the maple trees will increase the amount of leaf litter on the forest floor. They may not know how more oak leaf litter will affect the soil quality, or the soil food web, but they should be able to ask questions about what they would like to know in order to be more confident in their answers. For example, they may want to know which organisms decompose oak leaves, what compounds were in the maple leaves, who decomposed the maple leaves, etc.
Extend:
Students should use Part 2 of the worksheet to learn about the economic, or ecosystem benefits, of different trees. Then, students should use iTree Design to research how planting different trees will affect stormwater retention, air quality, energy conservation, and carbon storage.
Evaluate:
As a final assessment, give students Part 3 of the worksheet that corresponds to the topic that was studied (growth rates, decomposition, herbivory, phenology, and dispersal). More advanced students can be challenged by answering questions from other topics. Students should pay attention to the tradeoffs that are presented in each question, and should be able to explain how different trees offer different benefits and drawbacks depending on the ecosystem function that is of interest.
