Tree Survey: Point-Centered Quarter Sampling Method

1. Tree Survey

1. Establish a 150 m transect in the forest.
2. Place a stake every 50 m. Each stake (point) represents the center of four compass directions (N, E, W, S) that divide the sampling site into four quarters.
3. In each quarter, the distance is measured from the stake to the nearest tree ≥ 40 cm, regardless of species. Only one large tree per quarter should be measured, so a total of 16 trees are recorded in the large tree category. Record the distance in cm for each.
4. Collect a leaf sample from each tree. Be sure to note if the leaves are opposite, alternate, or wholred (Figure 1) before removing them. Place the sample on the herbarium paper, properly labeled with the tree number, and place in a plant press for later identification.
5. Using a field measurement tape, measure the diameter of the tree at 4½ feet above the existing grade (dbh). Record the dbh. If using a dbh tape, read the diameter directly off the tape. If using a regular measuring tape, measure the circumference of the tree and then calculate the diameter using the formula C = π d.
6. Repeat steps 1.3 – 1.5 for the nearest tree < 40 cm and > 2.5 cm in each quadrant. These trees are labeled the small tree category.
7. Using the leaf samples, identify the species of each tree in the 16 large trees and the 16 small trees categories.

Figure 1. Examples of opposite, alternate, and whorled leaf arrangements.

2. Calculations

(Do separate analyses for large trees and small trees.)

1. Calculate the mean point-to-tree distance for the entire sample of large trees, regardless of species. Calculate the mean point-to-tree distance for the entire sample of small trees, regardless of species.
2. Calculate the average density (the number of trees/hectare) for both the large trees and the small trees.
         
3. Determine the density by species for both the large trees and small trees. Then, count the number of individuals in the sample for each species and record (Table 1). The total number of individuals counted is 16.
            Relative Density = (number of individuals of a species/16) x 100%
   And
            Density = (Relative Density/100) x Average Density
4. Determine and record the basal area by species (Table 2).
   1. Convert the diameter measures into areas for all trees sampled (a = π r²).
   2. Calculate the mean basal area for each species, i.e. take the average.
   3. For each species, calculate the Basal Area and Relative Basal Area.
              Basal Area = Density x Average Basal Area
      And
              Relative Basal Area = (Basal Area / Total Basal Area) x 100
      The Total Basal Area is the total basal area for all species (sum all BAs).
5. Determine and record frequency by species (Table 3).
           Frequency = (no. of points at which species occurs/total no. of points sampled)
   And
           Relative Frequency = (Frequency/Total Frequency for all species) x 100
   1. The frequency of each species is determined by comparing the number of points at which that species occurred out of the 4 points sampled. For example, if an American Elm is found at all 4 of the points, the frequency would be 4/4 = 1. If a Silver Maple is found at 2 of the 4 points, the frequency would be 2/4 = 0.5.
6.  Calculate and record an Importance Value and Relative Importance Value by species (Table 4).
           Importance Value = Relative Density + Relative Frequency + Relative Basal Area
   And
           Relative Importance Value = (Importance Value /Total Imp. Value for all species) x100
7. Make a graph that depicts the importance value for each species on the y-axis and the species on the x-axis. Place them on the y-axis in order of Increasing Importance values. There should be one line for large trees and one line for small trees.

Large Trees
	# of individuals	Relative Density (%)	Density (trees/hectare)
Species 1 _______
Species 2 _______
Species 3 _______
Species 4 _______
Species 5 _______
Species 6 _______
Small Trees
	# of individuals	Relative Density (%)	Density (trees/hectare)
Species 1 _______
Species 2 _______
Species 3 _______
Species 4 _______
Species 5 _______
Species 6 _______

Table 1. A table to fill out information regarding the density of large and small trees.

Large Trees
	Average Basal Area  (m2)	Basal Area (m2)	Relative Basal Area
Species 1 _______________
Species 2 _______________
Species 3 _______________
Species 4 _______________
Species 5 _______________
Species 6 _______________
TOTAL		Total Basal Area =
Small Trees
	Average Basal Area  (m2)	Basal Area (m2)	Relative Basal Area
Species 1 _______________
Species 2 _______________
Species 3 _______________
Species 4 _______________
Species 5 _______________
Species 6 _______________
TOTAL		Total Basal Area =

Table 2. A table to fill out information regarding the basal area of large and small trees.

Large Trees
	# of points	Frequency	Relative Frequency
Species 1 _______________
Species 2 _______________
Species 3 _______________
Species 4 _______________
Species 5 _______________
Species 6 _______________
TOTAL		Total Frequency =
Small Trees
	# of points	Frequency	Relative Frequency
Species 1 _______________
Species 2 _______________
Species 3 _______________
Species 4 _______________
Species 5 _______________
Species 6 _______________
TOTAL		Total Frequency =

Table 3. A table to fill out information regarding the frequency of large and small trees.

Large Trees
	Relative Density	Relative Frequency	Relative Basal Area	Importance Value	Relative Importance Value
Species 1 _______________
Species 2 _______________
Species 3 _______________
Species 4 _______________
Species 5 _______________
Species 6 _______________
				Total IV =
Small Trees
	Relative Density	Relative Frequency	Relative Basal Area	Importance Value	Relative Importance Value
Species 1 _______________
Species 2 _______________
Species 3 _______________
Species 4 _______________
Species 5 _______________
Species 6 _______________
				Total IV =

Table 4. A table to fill out information regarding the Importance Value and Relative Importance Value of large and small trees.