1. Forest Sampling
Random Pairs Method

2. Sampling Trees per Acre
Follow a compass line of your choice
Starting with where you are standing (point P), look for the nearest tree (Tree A)
Only trees with a circumference of 18 in or more should be measured

4. Sampling Trees per Acre
Face Tree A and hold your
arms out to your side
Find the tree closest to tree A
that is behind the line formed by your arms. This is
Tree B
Do not select a tree in front of your line as Tree B

5. Sampling Trees per Acre
Measure the distance
between Tree A and B, record
the species of each tree and
circumference at breast height (DBH)
Return to point P and move 50 feet along the compass line and repeat the process
At least 10 pairs should be surveyed

6. Calculating Trees per Acre
After sampling is complete, use the formula below to calculate the number of trees per acre
Trees per acre= (AB)/(CD)
A=Square feet per acre (43,560 ft2)
B= number of pairs of trees randomly selected
C= 0.8 (a constant used for forests in our area)
D= Total area of the random pairs
Found by adding the squared distance of all of the random pairs

7. Calculating Trees per Acre
Sample problem:

8. Calculating Relative Density and Frequency
Calculated for each species identified in forest
Relative density= # of that tree/ total # of trees ID’d
Example: You identified 5 sugar maples out of a total of twenty trees
RD= 5/20 =25%
Calculating Relative Frequency
Relative Frequency= # of pairs species occurs in/ total # of pairs
Example: Sugar maples were ID’d in 5 out of 10 pairs
RF=5/10 =50%