Summary
Students will investigate the water cycle and how water flows through ecosystems. Students will use statistical analysis and mathematical reasoning to develop models that can determine the factors that contribute to a tree’s influence on matter and energy cycles within an ecosystem. Students will apply this knowledge to real life data sets to make predictions about how drought conditions may affect trees and the cycles they influence. Acknowledgement: This material is based on work supported by the National Science Foundation under Grant No. IIA-1301789. Any opinions, findings, and conclusions expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation or Oklahoma State Regents for Higher Education.
Essential Question(s)
Overarching Essential Question: How does matter cycle through ecosystems? Topical Essential Question: What part do trees play in natural cycles?
Snapshot
Engage
The students view a short video about forestry in Oklahoma and discuss the question, "Why are trees important?" During this discussion the students create a list of reasons they think that trees are important and share these reasons with the class.
Explore
Students create a mathematical model to measure and calculate leaf surface area. Students investigate tree transpiration by measuring the water use of a single tree limb over time and comparing this to stem size, limb length, and total leaf surface area. Students apply this mathematical model in an investigation to determine what factors most closely correlate with tree transpiration rates.
Explain
Students analyze their data using statistical analysis. Through this analysis students discover that total leaf surface area has the most impact on tree transpiration rates. Students observe tree anatomy to construct explanations for why leaf surface area had the greatest effect on transpiration. Students also create a model of the water cycle to identify how trees fit into that cycle.
Extend
Students read a journal article from the PINE MAP study (a study researching drought’s effect on Loblolly Pines) and identify similarities and differences between the research methods and results from the study and the students’ investigation.
Evaluate
Students are given real data from the PINE MAP research study and use their findings and models to analyze and make predictions regarding the Loblolly Pine and its response to drought as well as its role in the ecosystem.
Materials
Fresh Live Tree Branches, Bradford Pear works well. (1 per group)
1 cm graph paper
#10 Tin Can (1 per group)
Pruning Shears
Tape Measure or Meter Sticks
Graduated Cylinder (1 per group)
Plastic sheeting (e.g. plastic shopping bag or plastic wrap)
PINEMAP Journal Article (included) See http://www.pinemap.org/reports/annual-reports/Year_3_Annual_Report.pdf for more information.)
PINEMAP DATA (Included)
Microsoft Excel or other Statistical software
Excel spreadsheet instructions
CER statement template
PINEMAP Article reflection sheet
Engage
Show the students the Oklahoma forestry video clip starting at the beginning and ending at time mark 6:50.
Write the question, "Why are trees important?" on the board. Have the students take a sheet of paper and fold it in half lengthwise to create a two-column page. On the top of the left hand column have them write, "Why trees are important." Have them leave the right hand column blank for now. Instruct the students to individually begin creating a list of all the reasons they think trees are important in the left hand column.
Give the students enough time to generate a good list. Then have the students write, "How I Know It" at the top of the right hand column. For this part of the activity it is sometimes helpful to have the students work with a partner. Have the students write how they know each of the reasons they listed.
Use the round robin process (Have each group share one reasons why trees are important and how they know it, then move to another group. Each group shares a different reason until the most important reasons have been shared.) to have students share out with the class some of the reasons they think trees are important and how they know that information. As students share you can create a running list on the board.
Ask students, "When you buy fresh flowers, what is the first thing you should normally do when you get them home?"
Then ask the students, "Why do we put flowers in water?" and "What happens to the water over time?" "Where does the water go?
Show the students the short video clip "Water transport in trees" (https://www.youtube.com/watch?v=w6f2BiFiXiM).
To wrap up the introduction discussion draw students attention to how trees interact with water in an ecosystem. Students may not fully be aware of the role that trees play in moving water through an ecosystem at this point. Inform students that they will be investigating how trees accomplish the moving of water. Explain to the students that water that evaporates and exits the plant from the leaves is called transpiration.
Explore
PART 1. Investigation Set-Up
Tell the students that it is possible to do the same thing with trees and tree branches. As a part of the PINE MAP study, researchers are looking at drought and its effect on the growth of Loblolly Pine forests commonly grown for the lumber industry. In this study one thing that is measured is the transpiration rate (amount of water usage) for an average pine tree. One method for measuring this is by cutting down an entire tree and placing it in a bucket of water. The researchers can then measure exactly how much water the tree uses over a period of time (see image below). This is not much different than the setup for keeping Christmas trees alive after being cut down.
Tell the students that they will be investigating the factors that might be influencing water usage for individual tree limbs using a similar method. Explain to students that each group will receive a live tree branch a large #10 coffee can and the necessary measuring tools.
Show the students the sample set-up below for the investigation. Tell the students, “Before we can begin we need to define the parameters of our investigation. What characteristics of the tree branch could we measure and compare with transpiration rate (water usage) to find possible correlations?”
Once the students have identified the three characteristics to use as the independent variables the students will need to create a hypothesis and a null hypothesis for the investigation.
Students will also need to specify how each variable will be measured. This is important because during the data analysis, the class will combine and use all the data collected by the class(es). Consistency in the measurements will lead to a more accurate statistical analysis.
Show the students the suggested measurements methods (See figure below):
Tree limb length – Is measured vertically from floor to the top of the tallest point of the limb.
Tree limb diameter – Is measured directly at the top of the can.
Total leaf surface area – Will be described.
To measure Total leaf surface area students will need to construct a mathematical model to calculate total leaf surface area. The simplest and most common method for measuring leaf surface area is to use 1cm grid paper.
Place leaf on 1cm2 grid paper and trace.
Count the number of whole squares covered.
Count the number of partial squares covered. Divide this number by 2.
Add the number of whole squares to your answer from step 3. This is the surface area of the leaf.