Alien Plant Invasion: A Field Study project at Saguaro National Park
III. Setting Up a Study Plot / Collecting the Data
The students will investigate the question:
How extensive is the alien plant invasion
Students will have an area of the King's Canyon wash to divide into plots and study over the semester. This unit focuses on this one question, but further studies will be developed to look at alternate control strategies (for alien species) and their effectiveness.
Make sure students come prepared for the field trip. They should bring lunches, water, sunscreen, and hats.
To set up a study plot:
Students will be provided with a piece of graph paper showing a square, This will represent their 3x3 meter plot. Each square on the graph paper will equal 10 cm. On this paper, the students will "map" their plots with number of perennial plants* and the size of coverage of each plant. They will place the diameter of the base of each plant on the map, along with the diameter of the coverage area . If they know the name of the plant, this can be recorded in a key by numbering each plant and recording its name next to the number, on a separate piece of paper. If the identity of the plant is not known, they will describe it as fully as possible, and one representative plant will be taken (from outside the plot area) to be identified back in the classroom.
Plots will be measured in meters with a survey-type measuring tape. Each plot will be a 3x3 meter square. Only the southwest corner of the plot will be marked with stake and given an number labeled in paint. This will match the number the teacher records to identify the two students responsible for the plot.
The students will then begin measuring, in centimeters, the base** of each plant. The base of the plant consists of the primary stem or stems going down to its root system. This should be a diameter measurement. The actual coverage of the plant (how wide its leaves and stems overhang) is then measured as a diameter also. The coverage is how widely the plant spreads out over the ground. Students should measure the widest points. They will also need to measure how far the center of the plant is from the nearest two sides of the plot so it can be properly placed on the map. Overlapping may occur on the map if plants overhang one another in the plot. Each plant will be given its own number and have its own circles (showing coverage and diameter) on the map. Some circles may overlap other circles.
Back in the classroom, the plants' coverage is calculated by using the formula for the area of a circle: area = r 2 or the area of a circle = 3.14 x 1/2 diameter. Students identify the plants as native or non-native, enter the data into a spreadsheet, calculate the coverage for each plant, and determine the percent coverage by natives and non-natives plants. The percent coverage by natives and can be determined by putting the coverage totals for native plants over 90,000 (representing the area of the plot: 300 cm x 300 cm) and multiplying by 100. The same procedure can be used to determine the coverage for non-native plants. (More than 100% coverage is possible because plants overhang one another).
* Only perennial plants are counted and measured in this study because we will only be visiting the study site a few times a year. Annuals show up after rains and seasonally. Some annuals will only appear in the spring, while other appear only in the winter. We may not be there at the appropriate times to see the annuals, therefore we will focus on the perennial plants which are more permanent. There are also invader annual plants in the park, although I am not sure how much attention they are receiving.
** The base measurement is not used directly in this study for any calculations, but can give the students an idea of the age of a plant. If the diameter of the base and the coverage is similar, there is more mass than if the diameter of the bases is much smaller than the coverage diameter. The base measurement can be used for other questions if students want to study the issue in more depth.
Student directions for these activities are provided in the following handouts:
The University of Arizona
Department of Biochemistry and Molecular Biophysics
General Biology Program for Secondary Teachers