Invasive Species

Tulip Gardens

Invasive Species Exercises: Intensive Modified Whittaker Plot

The Intensive Modified Whittaker Plot is a small version of the standard Modified Whittaker Plot. It assesses cover of plant species in multiple subplots (1 square meter, 10 square meters, and 100 square meters) nested within a 100 square meter plot.

Setting up the Intensive Modified Whittaker Plot

  • Two 100-meter tapes
  • One 50-meter tape
  • 8 Ground stakes
  • ~25 Marking flags
  • Meter stick
  • One 0.5 by 2-meter subplot frame
  • One 2 by 5-meter subplot frame
  • Compass
  • 2.5-centimeter diameter soil increment core (if you are doing soil analysis too)
  • Plastic bags (for soil samples)
  • GPS unit
  • Reference materials (dichotomous floristic keys, etc)
  • Materials to collect unknowns

  1. Look around the area and determine the environmental gradient in order to position the long side (50 m) of the 1,000 square meter plot (K) parallel to the gradient. (The goal is to cover the most variation possible)
  2. Using two 100 m tapes (1 and 2), lay out the main plot (K) as a 20 x 50 m rectangle. Anchor tape ends at the starting point (right bottom corner, label 0,0). Using a compass to shoot a 90 degree angle, run tapes out following the arrows. Anchor the 20 m and 50 m corners
  3. Flag 7.5, 12.5, 35, and 55 m marks of tape (1), and 15, 35, 57.5, and 62.5 m marks of tape (2)
  4. Using a 50 m tape (3) and the flags marked at 7.5 m and 35 m of tape (1) and 15 m of tape (2), determine and anchor the starting point (0, 50 m) of subplot C (inner rectangle). Moving clockwise, lay out this subplot
  5. Take a magnetic azimuth (bearing) of tape (1) and tape (2) at the (0, 0) corner. Write it down in your field notebook with the plot name, site description and GPS coordinates from the GPS unit (Or use the site description sheet)
  6. Starting from the (0,0) point of K, walk to the 8 m mark of tape (1) and place the 0.5 x 2 m subplot frame along the inside boundary of the K plot. Record all of the species present within the subplot. Measure their average heights and determine (estimate) their percent cover. Flag unknown species as you encounter them, and make their labels (numbers) even if you aren’t collecting them right away
  7. When finished at this location, pick up the subplot frame and moving clockwise, repeat step 6 until all ten 1-square meter subplots are completed. There are six subplots around the inside of K plot, and four subplots around the outside of the C subplot
  8. Using flags and the subplot frame, set up subplots A and B. (Subplots A and B can be sampled in sequence with the 1-square meter subplots). Record the species present in the A, B, and C subplots
  9. Walk through the entire K (1,000-square meters) plot and record any species new to the plot
  10. Label and collect unknowns

Sampling Methods:

Within each 1 square meter plot, identify all vascular plant species, and estmiate the percent cover within the plot (to the nearest whole percent).
For the 10 square meter subplot, and the 100 square meter subplot, record all vacular plant species present.
Take a GPS reading at each plot and collect other data such as slope, aspect, and elevation for the plot.
Optional additional sampling procedures for cryptobiotic crust and soil conditions can be implemented according to the methods from the Modified Whittaker Plot page.


Colorado State University Warner College of Natural Resources