The Structure of a Quercus douglasii (Blue Oak) Population

1
The Structure of a Quercus douglasii (Blue Oak)
Population
Erika Teach Supervisor Ronald M.
Coleman Department of Biological Sciences
California State University, Sacramento
ABSTRACT 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.
Erika
Dr. Coleman
RESULTS and DISSCUSSION 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.
INTRODUCTION and OBJECTIVE 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 non-masting 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.
METHODS 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.
Figure 1 Survivorship of the blue oak population
in the greater Sacramento area by diameter at
breast height class (cm).
Figure 2 The diameter at breast height specific
fecundity of the blue oak population of the
greater Sacramento area.
CONCLUSION 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.
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.