The Structure of a Quercus douglasii (Blue Oak) Population
Erika Teach
Supervisor: Ronald M. Coleman
Department of Biological Sciences
California State University, Sacramento
Erika
Dr. Coleman
ABSTRACT
INTRODUCTION
and OBJECTIVE
I acquired data for this project from a tree
survey conducted by the Sacramento Tree
Foundation. The data included the estimate of the
total number of blue oaks within the greater
Sacramento area and percentages of that total in
each of seven diameter at breast height (dbh)
classes. I used that data to calculate the number
of individuals within each dbh class as well as the
fecundity. Those results were put into a static life
table within which I completed several
calculations. In order to project this information in
to the future and include masting I transferred the
data from the life table in to a Leslie Matrix. Within
the Leslie Matrix I used an IF statement with a
random number command included in it. The
random number represented the signal for the
tree to mast or not.
5.5
1.2
DBH Specific Survivorship (gx)
5
1
0.8
0.6
0.4
0.2
0
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
0-8
8-15
15-23 23-30 30-38
DBH class (cm)
38-46
54-61
0-8
Figure 1 Survivorship of the blue oak population in the greater Sacramento
area by diameter at breast height class (cm).
8-15
15-23 23-30 30-38
DBH Class (cm)
38-46
54-61
Figure 2 The diameter at breast height specific fecundity of the blue oak
population of the greater Sacramento area.
Blue Oak Population
In graphing the survivorship (Figure 1) this
organism appears to follow a Type III survivorship
curve as the survival among the young is very low
and then levels off in the larger dbh classes. The
graph of the dbh specific survivorship (Figure 2)
exhibits low survivorship among the first dbh class
with survivorship increasing with dbh size. Except
for dbh class 23-30, which dips to a low level. My
two thoughts on this are that this dip is either a
product of a static life table or that during the time
that the individuals in dbh class 23-30 were
produced there were not a lot of masting years that
occurred.
In graphing the finite rate of increase for the
population without masting there is a sharp drop
within the first year and after the fourth year it
levels (Figure 3). Figure 4 gives an adequate
representation of the proportional change in
population size from one time step to the next once
masting is added in to the Leslie Matrix.
400
350
Finite rate of increase (λ)
METHODS
DBH Specific Survivorship
Survivorship Curve
Survivorship (lx)
Blue oaks are found in woodlands and savannas
on almost three million acres of land in California as
well as in urban areas. Only about 40% of a
population will bear acorns at any one time. It is
estimated that 35% of those will germinate with less
than 5% growing past one year. During a nonmasting year individual blue oak trees can produce
up to 3000 acorns where as in a masting year they
can produce up to 16000 acorns. These masting
events are synchronized within populations of blue
oaks and occur about every 3 to 8 years. In order to
more accurately model a population of blue oaks it
would be important to include masting into the
model.
The purpose of this project was to incorporate
masting into a life table for a population of blue
oaks.
RESULTS and
DISSCUSSION
Masting can greatly change the structure of plant
populations. I incorporated masting into a life table
for the blue oak population in the greater
Sacramento Area.
CONCLUSION
300
250
200
150
100
50
0
1
2
3
4
5
6
7 8 9 10 11 12 13 14 15 16
Time (years)
Figure 3 Finite rate of increase without masting for the population of blue oaks
in the greater Sacramento area.
Figure 3 The finite rate of increase with masting for the population of blue oaks in the greater Sacramento area.
There are many factors that need to be
considered when modeling the life history of blue
oaks that I did not include in this model. Future life
history modeling could include such factors as
temperature, precipitation, and predation. All in all
I think this was a successful endeavor but in order
to get a more complete life history of the blue oak
population of the greater Sacramento area more
accurate data and other factors would need to be
taken in to consideration.