FOREST ECOLOGY LAB EXERCISE
Background
Forests are important ecosystems. In this laboratory exercise, you will be
simulating the methods used by forestry scientist in determining the ‘tree density’,
‘dominance’, and ‘frequency’. Each of these forest variables tells you something
slightly different about the makeup of the forest. In this exercise, you will come to
learn what each of these different values tells you about the forest.
Objectives
1. You should understand what forest data is used to determine ‘tree density’,
‘dominance’, and ‘frequency’, as well as understand the importance of each of
these measures in determining the ecology of the forest.
Materials
Forest
Basal Area & Species Data
NE
SE
SW
NW
Sample
1
Sample
2
Sample
3
Sample
4
Basal
Area
(ft2)
0.1
0.1
0.1
0.4
Species
Hickory
Red Oak
Red Bud
Red Oak
Basal
Area
(ft2)
0.1
0.2
2.6
0.3
Species
Red Bud
Red Oak
Burr Oak
Hickory
Basal
Area
(ft2)
4.1
0.2
0.4
0.1
Species
Burr Oak
Hickory
Red Oak
Red Oak
Basal
Area
(ft2)
0.5
0.2
0.4
0.1
Species
Red Oak
Red Oak
Burr Oak
Red Oak
Procedure
Forest
1. In order to estimate the ‘tree density’ in the forest given, you will be simulating
a standard method called the Point Quarter Method. Before applying this
method, we need to identify random points within the forest from which data
will be collected. Locate the following points using the values given below
and identify each point by making a small dot within the forest picture
provided.
For Example, for sample point 1, measure over 4.5 centimeters using the
scale on the bottom of the forest, and measure up 3.0 centimeters using the
scale on the left side of the forest. Draw a dot where these two measures
converge in the forest.
Horizontal Distance Vertical Distance
Sample Point 1
4.5
3.0
Sample Point 2
12.5
2.0
Sample Point 3
11
8.5
Sample Point 4
3
8.0
2. After finding each of the sample points, imagine two lines traveling through this
each point, a vertical north-south line and a horizontal east-west line. These
two lines would break the area surrounding each point into four quadrants, a
northeast quadrant (NE), southeast quadrant (SE), southwest quadrant (SW),
and northwest quadrant (NW). Hopefully you now understand why they call it
the Point Quarter Method. It might be beneficial for you to lightly sketch in
these imaginary lines through each sample point.
3. Next, measure the distance in meters (one centimeter equals one meter) to
the nearest tenth of a meter from each sample point to the nearest trees in
each of the four quadrants surrounding it. Record the measurements in
meters in the data table provided in question 1.
For example, you may measure the distance from sample point 1 to the
nearest tree in the NE quadrant as 1.5 centimeters. You would convert this to
1.5 meters and record it in the data table under sample 1, NE quadrant.
4. Next, determine the average distance from sample points to the nearest tree in
each quadrant by adding each of the distance measurements in the data
table in question 1 and the dividing by 16 (the total number of
measurements). Record this value in the appropriate space below the data
table in question 1.
5. Next, to determine the average open area surrounding each tree in the forest
in square feet, 1) square the value determined in step 4, and then 2) multiply
the value determined by 10.6 (there are 10.6 ft 2 per square meter). Record
this value in the appropriate space below the data table in question 1.
6. Finally, to determine the ‘tree density’ in acres, plug in the value calculated in
step 5 in the following equation. Record this final ‘tree density’ in trees per
acre in the appropriate space below the data table in question 1.
43,560 ft2 / average open area in ft2 = Density of Trees per acre
7. Answer question 2.
Basal Area & Species Data
1. The Point Quarter Method is used to determine more than an estimate of the
density of trees in a forest. It is also used to determine ‘tree dominance’ and
‘tree frequency’. ‘Tree dominance’ is determined by adding up the basal
area values for each species of tree in the samples taken. Since we are
simulating this laboratory exercise this data is given to you in the “Basal Area
& Species Data Table’ in the materials section. Use this data, determine the
total basal area for each tree species and record it in the table provided in
question 4.
2. For 2 point extra credit (so that you know how the values in the table were
calculated), determine the basal area in square feet of the log at the front of
the class, and record the value in question 5.
1) Measure the circumference of the log in feet to the nearest tenth of a foot
(1 foot 6 inches would equal 1.5 feet).
2) Use the following formula to determine the basal area in square feet.
Area circle =  (circumference / 2)2
3. Answer question 6.
4. To determine the ‘tree frequency’, determine the number of individuals for a
given species and divide that number by the 16 (the total number of trees in
the sample). To express your value as a percentage multiple your value by
100%. Determine the tree frequency for each tree species and record it in the
table provided in question 7. Your percentages should add up to 100%.
5. Answer question 8.
FOREST ECOLOGY LAB QUESTIONS
Name: ____________________________
Forest
1. Distance Measurements Data Table
Distance Measurements (cm)
Quadrant
Sample
1
Sample
2
Sample
3
Sample
4
NE
SE
SW
NW
Average Distance
= _________________ meters
Average Open Area
= _________________ square feet
Tree Density
= _________________ trees / acre
2. What does the tree density tell you about a forest? What would be different
about forests having a lesser or greater tree density?
3. Do you think old growth forests may have a different density than young
forests? Explain.
4. Tree Dominance Data Table
Total Basal Area
(square feet)
Burr Oak
Red Oak
Hickory
Red Bud
5. Extra Credit
Basal Area
= _______________ square feet
6. Based on the ‘Basal Area Data’ for each species which species would you
consider to be the most dominant species? The least dominant species?
Explain.
7. Tree Frequency Data Table
Frequency
as a percentage
Burr Oak
Red Oak
Hickory
Red Bud
8. Based on the ‘Tree Frequency Data’ for each species, which species do you
consider to be the most dominant species? The least dominant species?
Explain.