Make or obtain a frequency grid. The grid is comprised of a metal or PVC frame, 75 cm x 75 cm, that has been divided into 25 cells, each 15 cm x 15 cm.

Place the grid on the soil surface at a random location in the plot. Avoid areas that are not representative of the plot (e.g., adjacent to sampling equipment, on plot edges). Count the number of cells that contain at least one plant of the target species. Flip the grid over, end-to-end, and count again. Repeat two more times, for a total of 4 counts (100 cells). Add the 4 counts together.

To calculate the frequency of occurrence, divide the total number of cells that contain the target plant by 100 (the total number of cells counted). To estimate the number of plants per m2, divide the total number of cells that contain the target plant by 2.25 (area of each cell= 0.0225 m2, multiplied by 100 cells).

Reference

Vogel, K.P. and R.A. Masters. 2001. Frequency grid: A simple tool for measuring grassland establishment. Journal of Range Management. 54: 653-655.