Prairie Lab
Tips for revising your lab
General
• Carefully read the instructions in:
– The Prairie Lab handout
– The Lab Grading, Lab Reports, & Worksheets handout
• Use headings to organize your report
– Appropriate headings are INTRODUCTION, METHODS,
RESULTS, DISCUSSION, and LITERATURE CITED
– Put your figures and tables in the results section, not at the end
of your paper
– Save space by starting each section immediately after the
preceding section
• Affect is a verb, effect is a noun
• The ½m2 sampling area was a “quadrat”, not “quadrant”
Introduction
• Provide background information on prairies, fire, soil, etc.
– Provides context for the your lab report
– Acknowledges previous studies on the subject
– Citations are appropriate and encouraged
• Clearly state the purpose of the lab
– This is given in the lab handout
– The purpose is not to identify your unknown plot (its broader than that)
• Clearly state a hypothesis and specific predictions
– A hypothesis is a general relationship between fire and prairie
– Predictions are more specific, for example:
• As fire frequency increases, the mean species frequency of grasses will
decrease
• Prairies burned every year will have a greater species richness than prairies
burned less often
– If you predictions turn out to be true, it lends support to your hypothesis
• Don’t mention Tucker Prairie here, save that for the methods
Methods 1
• Give a site description
– Include information relevant to our lab, such as the location,
history, and dominant plant species of Tucker Prairie
– There is a good site description in the handout. For our purposes
you don’t need to cite the handout
• Describe the experimental design
– How many experimental plots are there? How often is each one
burned? Are there any differences between the two controls?
How long has the experiment been conducted?
• Give the dates of data collection
– This is context, so a reader knows what species are expected to
be present, at what stage of growth, and how long it has been
since the spring burn
Methods 2
• Describe the data collection
– Use first person, past tense, active voice:
• “We identified the plants in each quadrat.”
– Don’t describe how your day went, just describe how the data was
collected:
• No: “On the second day our TA gave us an unknown plot and told us to …”
• Yes: “We then sampled 20 quadrats on a plot of unknown burn frequency
using the same methods…”
– Specify your sample sizes exactly
• How many quadrats per experimental plot? How many quadrats total? How
many quadrats on your unknown plot?
– Include how the biomass data was collected
• What did you do? On how many quadrats? Did you divide the material into
categories? What categories? What did I do with the plant material after you
collected it?
• Its not necessary to say that you used clippers to cut the vegation and put it
in brown paper bags with your name on them. That’s not important. Just say
that you collected the vegetation, divided it into categories, and I weighed it.
Methods 3
• Describe the data analysis
– Again, specify sample size
• How many quadrats are you analyzing on each experimental plot? Why is
this more than the number of quadrats your group sampled personally? How
many quadrats are you analyzing for your unknown plot?
– What program did you use to analyze the data
• You don’t have to say that you entered the data in a table and analyzed it…
that’s assumed.
– What categories did you divide the plant species into for analysis?
– What metrics did you calculate? In our case, we calculated the mean
species frequency of each group (explain how), and the number of
species in each group, also known as species richness, or more loosely,
species diversity
– How did you analyze your biomass data? (Hint: you should have
calculated the % biomass of the 3 plant categories [excluding downed
litter].
Results
•
•
Don’t present the same data in both a table AND a figure
Follow the guidelines from the previous help file on how to create figures and tables,
most importanly:
–
–
•
•
Have a detailed description. In our case, its important to know what the significance of the
lines vs. columns is
Include 2 axis labels on the figure we created
Feel free to include a category for your unknown plot in your figure, so you can more
easily compare the values with the experimental plots
In words, describe your results
–
Good style
•
•
•
•
•
–
In your text, feel free to abbreviate mean species frequency after the first usage
•
•
•
“The MSF of grasses increased with burn frequency (Figure 1).”
“Species richness of woody vegetation was highest in the control plots (Figure 1).”
“The east control plot contained more species of forbs than the west (Figure 1).”
“Biomass on our unknown plot consisted of 60% grass, 30% forbs, and 10% woody vegetation (Table
1).
“Our unknown plot showed approximately the same MSF of grasses as the 5-year burn plot (Figure 1).
E.g.: “We measured mean species frequency (MSF). The MSF of grasses…”
Any results that you want to mention in your discussion should first be stated here
Do not discuss WHY you observed the results you did here, save that for the
discussion
Discussion
•
Relate your results to your predictions and hypothesis
–
–
•
•
Avoid ambiguous terms like “more grasses”. Use specific terms like MSF.
Why did you observe the patterns you did?
–
–
–
–
–
•
•
•
Say whether your data agrees with your predictions. What does this say about your
hypothesis?
Note that you cannot “prove” your hypothesis, only provide evidence which supports or does
not support your hypothesis
What is it about grasses that causes them to occur more frequently in oft-burned areas.
Why do trees not deal well with frequent fire?
How does downed litter affect the ability of seeds to germinate?
How does the claypan affect the growth of the 3 categories of plants?
How does a rainy year like this one affect the abundance of the 3 categories of plants?
The articles we provided are chock-full of potential reasons, e.g. answers to the
above questions and more. Dig around a bit to find some (cite your references).
Compare your results to those of other studies (cite them).
Tell me the frequency at which you think your unknown plot has been burned. Note
that this is different than telling me the last time it was burned.
–
–
Compare your biomass results to table 5 in Kucera (1990). Be sure to cite him if appropriate.
You collected MSF and species richness data on your unknown plots… use it to help justify
your claim.
Some things to get your brain
juices flowing
•
•
•
•
•
•
The claypan is impermeable to water
Grasses can penetrate the claypan somewhat, forbs and woody species cannot
Some grasses do well in dry conditions because they are C4 plants and therefore
have more efficient water regulation than forbs and woody species
All species need light to grow. Litter blocks light. Grass seeds are small, so weak
grass seedlings cannot push lots of litter out of the way to reach the sun. Forb and
woody species have stronger seedlings and can push through the litter.
The apical meristem, or “growing part” of a grass is at ground level, and is not
destroyed by a fire. The apical meristems of forbs and woody species are above
ground, at the leaf buds.
The majority of grass biomass is below ground. The majority is above ground in
woody species. Forbs are somewhere in between. This makes it harder for
trees/forbs to come back after a fire.
•
Any one of the readings should discuss one or two of these subjects.
•
You don’t need to understand all of these mechanisms, or talk about all of them. You
should, however, try to come up with at least a couple of semi-plausible reasons why
you observed some of the patterns you did. There are definitely more mechanisms
than those listed above that you can glean from the readings.