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 Erika 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. 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.