the links here to jump to major sections on the page or just scroll
down to explore on your own:
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.
Are the Steps of the Scientific Method?
- Create a Question:
Something interests you, but you don't
know how or why it works
Make a guess about how or why
- Experiment: Plan
a way to test your hypothesis
- Observation: Look
at your experiment and record what you see
- Analysis: Graph
your data and look for patterns
- Conclusions: Decide
what your data means and if it supports your hypothesis
- New Questions: Based
on your conclusions, what new questions do you have?
Introduction to Greenhouse Gases and
Tree Growth Experiment
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.
1: Creating a Question
Photosynthesis and Greenhouse
the FACE facility near Rhinelander is based on two fundamental ideas:
- Trees must have carbon dioxide (CO2)
to make food through photosynthesis
- Because of human activities, levels of CO2
and other greenhouse gases like ozone (O3)
are increasing in the atmosphere
Scientists know that carbon dioxide
(CO2) is an important part of photosynthesis
which is the process that trees use to make food.
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
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.
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.
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.
remember: because of human activities like burning fossil fuels,
levels of CO2 and O3 are increasing in the
2: Creating an Hypothesis
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.
- with higher levels of CO2,
trees should grow bigger and taller in less time
- with higher levels of O3,
trees should grow more slowly
- with a combination of high CO2
and high O3, the positive effects of CO2
should be balanced by the negative effects of O3.
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:
- High CO2
- High O3
- High CO2 and high O3
- Control (this how the plot grows when we
don't do anything to it)
each of the plots we will look at 4 variables to test our hypothesis:
- Tree height (how tall do they get in each
- Leaf drop date (when do the leaves come off
of the trees in the Fall?)
- Leaf mass (how much do all of the leaves
in each plot weigh?)
- Leaf area (how big is the surface area of
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
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
for each plot.
Finally, we run our sample leaves through
an analyzer to measure their surface area.
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
Plot 1 = high carbon dioxide
Plot 2 = high ozone
Plot 3 = high carbon dioxide and high ozone
Plot 4 = control group
6: Deciding What Your Observations and Data Mean
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.
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
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.
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
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?