The basic idea behind PCQ sampling is quite simple. You randomly select a point in the forest. Using a compass, you divide the area around this point into four quadrants (northeast, southeast, southwest, northwest). Within each quadrant, you then locate the tree that is nearest to the point center. For this tree, you then record three pieces of information:
1. Distance to the tree in meters
2. Diameter of the tree at breast height (DBH) in centimenters. Note that “breast height” is defined as 1.37m above the ground on the uphill side of the tree. Note that, in order to be counted, a tree must be at least 10 cm DBH at 1.37m above the ground.
3. Species of the tree.
4. Tree height (this is not normally part of PCQ measurements but we would like to have this information to compare with the LIDAR-based tree height measurements; more on this below)
At each point, this means that you will be recording data for only FOUR trees. The arrangement might look something like this;