Modelling the persistence of an apparently immortal Banksia species after fire and land clearing

A stage-based model was developed for the population dynamics of Banksia go odii, a rare long-lived shrub in Western Australia. While few seeds are pro duced, death of adults due to senescence or fire has yet to be observed. A sensitivity analysis showed that population growth is close to zero as long as post-fire mortality and recruitment are within their usual low bounds. To remain viable, the size of a population remnant should exceed about 80 i ndividuals. If fires occur at random intervals, an average of one fire in 1 0-15 years is optimal. Regular fires should have inter-fire periods of 15-2 0 years. Loss of adult plants due to human activities, such as land clearin g, will increase mortality beyond its natural bounds and cannot be compensa ted for, due to the low fecundity of this species. Hand sowing after a fire may raise establishment by orders of magnitude and achieve a permanent pop ulation increase within the first year. Conservation authorities should tar get the sensitive factors through active management at the recruitment stag e and by ensuring that no further loss of mature plants takes place through land clearance. (C) 1999 Elsevier Science Ltd. All rights reserved.