Environmental Engineering Reference
In-Depth Information
Analysis of Point-Quarter Data
The final product of your calculations should be a table that looks like this
(Table
5.1
):
Frequency
(no. of
plots)
Mean basal
area per
tree (m
2
)
Mean basal
area/ha
(m
2
/ha)
Relative
frequency
Density
(trees/ha)
Relative
density
Relative
basal area
Species
Total
Use the questions and formulas below to fill in the table using the class data.
How common is each species?
1. We can answer this question by simply looking at the number of points that each
species occurs in.
Frequency
¼
no
:
points that the species occurs at
How frequent is each species relative to the total?
2. If you counted 40 plots total, and 4 of these had white pines, white pines would
represent 4/40, or 0.10 of the total points.
Relative frequency
¼
no
:
of plots containing species A
=
total no
:
of plots
What was the total density of all trees in the site?
3. The first step in analyzing point quarter data is to determine the mean point-to-
plant distance for all of the trees on each transect. This value represents the mean
distance between trees in the site. Compute this value and write it here:
Mean point-plant distance for ALL trees
¼
m
4. Next we need to compute tree densities. The mean point-to-plant distance
squared (d
2
) gives the mean area per tree.
m
2
¼
Mean area per tree over all species
By knowing the mean area per tree, we can figure out how many of them are
contained in a defined area (usually a hectare (ha), which contains 10,000 m
2
).
