Conservation requirements of an exploited wildflower: modelling the effects of plant age, growing conditions and harvesting intensity

Abstract

When flowers are harvested from wild plants an issue for conservation managers is whether sufficient seeds remain for population replacement, especially if it is subject to recurrent disturbance. Field data on the effect of flower picking on seed availability over 13 years were available for the most heavily exploited wildflower in Australia, Banksia hookeriana, a fire-killed shrub restricted to a 2000 km 2 area in the northern sandplains of southwestern Australia. These were combined with demographic data from 14 long-term monitoring plots scattered over the landscape. Growing conditions were termed ‘good’ to ‘poor’ depending on how they affected the number of inflorescences produced, and recruitment of young plants. A computer model was developed based on best-fit equations for all key processes accounting for seed and seedling production and loss. The model indicates that self-replacement (maintenance of a stable population size at a given age from one generation to the next) is unlikely for the first 5–11 years following fire, depending on growing conditions, even in the absence of picking. Picking has little effect on the minimum fire interval for self-replacement under good growing conditions, but, under poor conditions, minimum fire interval rises from 12 years at 0% picking to 20 years at 30% picking. Miscalculation of the intensity of picking allowable could have serious consequences for conservation of wild populations, as fires are most likely at 10–20 year intervals. A second computer model took inter-fire establishment into account. It gave similar results for self-replacement conditions, but also indicated that the level of picking that could be sustained diminishes sharply once fires occur at intervals >20 years. We suggest caution be exercised by conservation authorities in setting the age to first picking and the levels of picking permitted for wild populations of Banksia hookeriana. Our models are suitable for a wide range of vulnerable, fire-killed species at present harvested from the wild.