A STOCHASTIC-MODEL FOR THE VIABILITY OF BANKSIA-CUNEATA POPULATIONS - ENVIRONMENTAL, DEMOGRAPHIC AND GENETIC-EFFECTS

1. The dynamics and life history of a population of Banksia cuneata are described in relation to natural variation in rainfall and the frequency of prescribed (controlled) fires and wildfires. 2. These factors are combined in a stochastic population model for the population that includes demographic, environmental and genetic factors. The purpose of the model is to evaluate the effects of different management options on the expected population size and on the risks of population decline and extinction. 3. Management options to maximize population size and to minimize risks of extinction are different. A moderate frequency of prescribed fires (at intervals of 15-25 years) is predicted to result in increases in the mean population size. However, it also results in risks of extinction of the population of about 50%, because seedlings that establish after a fire are highly susceptible to drought. The risks of extinction are minimized if the frequency of fires is kept as low as possible. However, this leads to a substantial decline in the size of the population. 4. If, over the next 50 years, there is a reduction in average annual rainfall in the region, the chances of persistence of the populations are low, even in the absence of prescribed fires. The only way to ensure a reasonable chance of persistence for the populations is to intervene by watering seedlings whenever there is severe drought following a fire. 5. These results are exploratory because the model is based on scant data. The most important need is to estimate better the relationship between rainfall and the number of seedlings recruited into the population per adult.