Conducting and Analyzing Biodiversity Surveys

How many kinds of plants live around you? Which plants are common and which are rare? Are some areas more diverse than others? What is the average tree size? When does plants flower? How can you answer these questions? Conduct a plant diversity study.

Dichotomous keys were first used in 1778, and they remain the "industry standard" in reference books. At each step in a dichotomous key, there are 2 contrasting choices, no more and no less. Each choice in the series determines the next possible options.

Brainstorm with your fellow students and decide what you want to learn about the biodiversity in your local area. Would you like to maintain a permanent plot for future classes? In addition to noting changes in the number and kind of plants present, your school could monitor changes in flowering times from year to year.

As field biologists looking at local plant diversity, you and your classmates also need to plan your research. Are there too many plant species in the local environment - whether the schoolyard or city park - to survey them all? Your class can decide to survey the trees only or the trees and shrubs or the herbs only. Would similar-sized plots work equally well for surveying trees or herbs?

Below are some sample plot designs. Discuss the advantages and disadvantages of different plot designs. Determine a size plot to fit the goal of your class survey.

2 meters long by 2 meters wide

20 meters long by 2 meters wide divided into subunits of 2 X 2 meters (long, narrow plots are transects)

100 meters long by 100 meters wide divided into subunits of 25 X 25 meters

In your field notebook, write down the research questions and the plans your class devised to answer them. Try to imagine problems that might complicate your plans to survey plant diversity. Develop strategies to deal with these problems should they arise.

Study a local field guide to learn some plants you'll likely encounter is your survey.

Now you’re ready for fieldwork

Materials for Surveying Plant Diversity

1. Look over the survey site, considering the variety of plants and habitats. Make a guess about how many kinds of plants are present in the area.
2. As a class, determine where to mark out the plots (or place a frame for small plots). Aim to survey at least three plots. If possible, survey more than one habitat type.
3. Work in large teams to mark out the plots. Place a stake in each corner, measure the correct length and width, and mark off straight lines of the plot using string and a compass. Mark off subplots with string and stakes or draw distinct lines on the string with a permanent pen.
4. Work in teams of three to six students to conduct the survey. Each team will be responsible for collecting data on a small area within the plot or a small plot.
• One team member will record the data (use the sample sheet or create your own).
• One or two members will inspect each plant in the survey area and report the information to the data recorder. Work carefully to avoid counting the same plant twice or dead plants. If you do not know the name of a plant and cannot identify it using a local field guide, give the plant a preliminary name such as Mystery tree #1 or Unknown shrub # A and note a general description of the plant.
• If your class is collecting specimens in conjunction with the plant survey, additional team members will be responsible for collecting and pressing the specimens.
• If your class is asking questions about the distribution of plant species within the local environment, one team member will be responsible for mapping where on the plot the plants are found.
• If your class is collecting information about when plants produce flowers, fruits, and new leaves, one team member will be responsible for recording this information.
5. Complete the survey and analyze the data.

How close was your guess to the number of plant species recorded from the survey?

Get the most from your survey data by crunching the numbers. Find out which plant is the most common in each plot and calculate the biodiversity of your local area. Before moving on to the next step, make sure you know the size of the area you surveyed. Why do you think it is important to know the total area surveyed?

Calculate it

Materials for Analyzing and Presenting Plant Data

For each plot, calculate:

Density = the number of individuals per unit area (also called abundance)

Diversity = the number of species per unit area (also called species richness)

Combine all plot data to calculate:

Relative density = the number of individuals of species A X 100
                                  the total number of individuals

(also called relative abundance or frequency)

Frequency rate = the number of plots with species A X 100
                                  the total number of plots

Interpret it

Were some plots more diverse than others? Compare and contrast the plots and habitats studied. List some possible differences between the plots and give some reasons why some areas have higher diversity (species richness) than others. How would diversity differ in a city park, an old field, a forest, or a prairie?

Do you think your survey data accurately describes the plant diversity in your area? What might influence whether a survey is accurate or biased?

What does the graph at right show? How is this important to biodiversity surveys?

Think about biodiversity a bit more...

How do humans influence the abundance and diversity of plants in different areas?

Why does diversity matter? Does high plant diversity have advantages? How do animals rely on plants? Design a study to test the hypothesis high plant diversity leads to high animal diversity.

Are some plants common in all plots and others found only in a few plots? Do different kinds of plants grow in different areas (e.g., in the shade near a stream or south-facing slopes or clay soils)? In addition to answering questions on diversity, surveys provide data on the distribution of plants in the environment. What biotic and abiotic factors influence where plants grow locally? What variables would you record to test these ideas?

Plant diversity data sheet

Plot # 1 Description of plot location and site: ________________________________