Use the links here to jump to major sections on the page or just scroll down to explore on your own:

• Introduction
  • What is the Scientific Method?
• What are the Steps of the Scientific Method?
• Experiment Background
• Step 1: Creating a Question
  • Photosynthesis
  • Greenhouse Gases
• Step 2: Creating an Hypothesis
• Step 3: Setting up an Experiment
• Step 4: Observing and Collecting Data
• Step 5: Graphing and Analyzing Data
• Step 6: Deciding What Your Observations and Data Mean
  • Tree Height
  • Drop Date
  • Leaf Weight
  • Leaf Area
  • Step 7: Asking New Questions Based on Your Conclusions

Introduction
What Is the Scientific Method?
When scientists do their work, they usually begin with a question about something they see in the world around them. They follow a specific approach called the scientific method for figuring out possible answers. By following this method, they can get results that help to show other scientists why their answers make sense.

What Are the Steps of the Scientific Method?

1. Create a Question: Something interests you, but you don't know how or why it works
2. Hypothesis: Make a guess about how or why
3. Experiment: Plan a way to test your hypothesis
4. Observation: Look at your experiment and record what you see
5. Analysis: Graph your data and look for patterns
6. Conclusions: Decide what your data means and if it supports your hypothesis
7. New Questions: Based on your conclusions, what new questions do you have?

Experiment Background
Introduction to Greenhouse Gases and Tree Growth Experiment
The research activities of this project are based at the 80 acre FACE facility near Rhinelander, Wisconsin. Ecologists in this study examine how tree growth is affected by greenhouse gases. To simulate the atmospheric conditions of the year 2050, which will be quite different from today, rings of trees are surrounded by large PVC tubes that blow out carbon dioxide (CO₂) and ozone (O₃). Ecologists take many samples and measurements to see how the trees respond - they examine everything from root tip to shoot tip.

Step 1: Creating a Question
Photosynthesis and Greenhouse Gases
Research the FACE facility near Rhinelander is based on two fundamental ideas:

1. Trees must have carbon dioxide (CO₂) to make food through photosynthesis
2. Because of human activities, levels of CO₂ and other greenhouse gases like ozone (O₃) are increasing in the atmosphere

Photosynthesis
Scientists know that carbon dioxide (CO₂) is an important part of photosynthesis which is the process that trees use to make food.

(CO₂) enters through tiny openings called stomata on the underside of leaves. Chloroplasts (a kind of energy processor) change the (CO₂) and water collected from the roots into glucose (a kind of sugar used as food by trees and other plants).

Ozone (O₃) also enters the stomata and damages chloroplasts. This disrupts glucose production and slows tree growth.

So remember: CO₂ is fuel for tree growth, but O₃ is harmful and slows growth.

For more information on photosynthesis, click here to visit the Science section at BrainPop.

Greenhouse Gases
When people talk about the greenhouse effect, they mean that the temperatures on earth are getting warmer. Just like the glass in a greenhouse, the atmosphere surrounding the earth lets heat energy in but won't let it back out.

The greenhouse effect happens when certain gases like carbon dioxide (CO₂) and ozone (O₃) are produced by burning fossil fuels such as coal and gasoline. These build up in the atmosphere and trap heat energy.

So remember: because of human activities like burning fossil fuels, levels of CO₂ and O₃ are increasing in the atmosphere.

Step 2: Creating an Hypothesis
Human activities are increasing levels of CO₂ and O₃ in the atmosphere.

CO₂ is an important part of photosynthesis and helping trees to make food and grow.

O₃ is a phytotoxin (meaning it is poisonous to plants). Exposure to O₃ damages leaves and slows growth.

Therefore,

1. with higher levels of CO₂, trees should grow bigger and taller in less time
2. with higher levels of O₃, trees should grow more slowly
3. with a combination of high CO₂ and high O₃, the positive effects of CO₂ should be balanced by the negative effects of O₃.

Step 3: Setting up the Experiment
In order to test our hypothesis, we are going to set up 4 test plots and record our observations about 4 variables (these are the things like tree height that are likely to be different in each plot).

In these plots the trees will be surrounded by large PVC tubes that release specific amounts of CO₂ or O₃ or both. These gases will simulate what the atmosphere may look like in 2050 if we continue burning fossil fuels at the rate we are now.

The test plots we will use are:

1. High CO₂
2. High O₃
3. High CO₂ and high O₃
4. Control (this how the plot grows when we don't do anything to it)

In each of the plots we will look at 4 variables to test our hypothesis:

1. Tree height (how tall do they get in each plot?)
2. Leaf drop date (when do the leaves come off of the trees in the Fall?)
3. Leaf mass (how much do all of the leaves in each plot weigh?)
4. Leaf area (how big is the surface area of each leaf?)

Step 4: Observing and Collecting Data

In the first part of the data collection, we will measure and record tree height in each of the plots.

Next, we collect falling leaves in the plots using leaf litter baskets.

 

We record the date when we estimate that 50 percent of the leaves have fallen from the trees in the plots into our leaf litter baskets.

Using the samples we collect with our litter traps (baskets), we weigh the samples and estimate the total leaf weight for each plot.

Finally, we run our sample leaves through an analyzer to measure their surface area.

 

Step 5: Graphing and Analyzing Data
Looking at the graphs of data from our four plots and the four variables, what patterns do you see? Use the key here to identify which gas treatment was applied to which plot.

Plot 1 = high carbon dioxide
Plot 2 = high ozone
Plot 3 = high carbon dioxide and high ozone
Plot 4 = control group

Step 6: Deciding What Your Observations and Data Mean
Tree Height
We can see that trees exposed to higher levels of carbon dioxide grow taller more quickly. High ozone exposure, though, has the opposite effect. These trees are the shortest. These findings support our hypothesis that elevated CO₂ will increase growth while elevated O₃ will reduce growth.

Interestingly, we can see that the control group (the one growing without any alteration) has almost the same height as the trees exposed to both carbon dioxide and ozone. From this, we can conclude that higher levels of CO₂ balances the impact of O₃ on leaf physiology.

Leaf Drop Date
From the graph, we can see that trees exposed to high CO₂ retained leaves the longest while trees exposed to O₃ retained leaves the shortest. The control group retained leaves for less time than the CO₂ trees but longer than trees exposed to CO₂ plus O₃.

We can conclude that higher levels of CO₂ help trees to photosynthesize (make food) longer into the Fall. High O₃, on the other hand, shortens time for photosynthesis (the growing season) by causing leaves to senesce sooner and fall off.

Leaf Weight
From the graph we can see that trees exposed to high CO₂ produced the most leaves while trees exposed to high O₃ produced the fewest leaves. The CO₂ + O₃ plots produced slightly more leaves than ones from the control plot and quite a bit more than the O₃ trees.

We can conclude that higher levels of CO₂ lead trees to produce a greater amount of leaves. This improves their light capturing ability and leads to increased photosynthesis (food production). Because leaves contain nutrients like nitrogen and phosphorous, more leaves also means more nutrients being released to the soil when the leaves fall off. High O₃, on the other hand, leads to fewer leaves to capture light and photosynthesize.

Leaf Area
Our leaf area index data show us that elevated CO₂ increases leaf mass while elevated O₃ decreases leaf mass. The results for the plot with both gases fall in between. These findings are important because more leaves may mean more capture of sunlight. An increase in light capture would mean that trees are able to make more food.

Step 7: Use Your Findings to Ask New Questions
Once we have supported or disproved our original hypotheses, we can begin to ask new questions based on what we have learned. Some questions we might ask after seeing the data from the FACE site are:

Does increased leaf area lead to increased light capture by trees?

Does increased light capture lead to increased photosynthesis and tree growth?

Does increased leaf area and increased light capture lower the light that gets to understory plants? Does this change the kinds of plant species that grow in the understory?

Does an increase in leaf area have an effect on ecosystems in terms of the animals and parasites that live there?

Does an increase in leaf area lead to an increase in water usage?