Environmental Engineering Reference
In-Depth Information
3. How do species rankings by density compare to rankings by basal area?
4. Draw a forest stand in which species A has high density and low basal area,
while species B has low density and high basal area.
5. In order to determine the importance or overall magnitude of a species impact on
an ecosystem, we sometimes calculate importance values (IVs). IVs combine all
aspects of a species influence into a single number.
IV
¼
relative density
þ
relative frequency
þ
relative basal area
Relative values are simply the value of the species divided by the total for all
species (taken from Table
5.1
). Create a second table of importance values for
the different species in your site:
Species
Relative Density
Relative BA
Relative Freq.
IV
6. Use the data in Table
5.2
to answer the following questions:
A. Which species had the highest importance value?
B. Which species had the lowest IV?
7. Draw a forest stand in which Species A has a very high IV and Species B has a
very low IV.
8. If two species have the same IV, does that mean that they influence the
ecosystem in the same ways? Why or why not?
Size-Class Distributions
One way to investigate successional trends in a forested wetland or any forested
system is to construct size-class distributions for the different important species.
Size-class distributions can be graphically represented by plotting the number of
trees in different size classes (e.g., 1, 2, 5, 10 cm classes, Fig.
5.13
).
9. Create size-class distribution plots for the three species with the highest IVs.
10. What do these size-class distribution plots tell you about the future of the
forest?
