BACKGROUND: You have just been given the task of finding out how many dandelions or how many blades of grass are on your school grounds. How would you go about finding out? Your problem is similar to the problems scientists face all the time. How many whooping cranes are in existence? How many deer in a forest preserve? How many compass plants are in a section of prairie? You might solve your problem by getting down on your hands and knees and counting every dandelion on the school grounds. This might take you a very long time but if done carefully would give you a precise answer.
It is often unrealistic for a scientist to count every organism in her/his research area. What scientists often do is to work with a sample, a small section or plot of their research area. From their sample the scientist can then estimate many things about their research area without having spent all the time necessary to count each organism.
In this study the samples you will work with will be a meter on each side or a one meter square quadrat. From these samples you will be able to discover a great deal of information about your school ground ecosystem.
PROCEDURE: In this exercise students will work in groups of four using the data sheets.
Describe "quadrat," how it is used and how one is made.
Show the students where to set up their quadrats.
It is not important that the students know the names of all of the plants in the school's lawn. Have each group of students assign each type of plant with a number, letter or a name they make up. Do this for all of the plants except the grasses; these should be represented with crosshatching. Use horizontal crosshatching to represent the first type of grass then vertical and various angles if your students can determine that there are other types of grass present.
Using two meter sticks and grid the data sheet, have the students map the location of the plants in their quadrat. First draw in the grasses using the crosshatching code. Once the grasses have been drawn in, the students will use the meter sticks to get the exact location for each of the other plants and indicate their locations on the recording page using the proper symbols.
Students need to get an accurate count for each species present in their quadrat and record this on the plant code sheet. For our purpose we will count each stem of grass as a separate plant. If there is simply too much grass to count this way, count the grass in a half or a quarter or a hundreth of your quadrat and multiply by the appropriate number.
Now students can determine the percent of cover for each species and record it on their chart data page.
When you do a study like this at the Fermilab prairie, students will enter their data into a computer and that computer will calculate something called an Importance Value. This value tells us how important a plant is to the area. Since you do not have this computer and software at your school, we will try a simple version for this. Have students look at the number found and % cover for their plants. Ask them to determine which plant they think is the dominant or most important plant in their study.
Species diversity is very important to the stability of an ecosystem. If many different species are present, then the loss of one or two will probably not have a great effect. But if species diversity is low, the loss of one or two could have a major impact. In the original prairie of Illinois species diversity was probably twenty-five different species per square meter. Calculate the species diversity for your quadrat by counting the number of different types of plants you found. Species diversity = _____per square meter. How does the species diversity of your school lawn compare to that of the prairie? Which ecosystem would be more stable?
How many of each type of plant are on your entire school grounds? How could you figure this out? DO IT!
Scientists do not base their calculations on just one quadrat as you just did. Instead they will use the data from many quadrats. Why do you think they do this?