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

When flowers are harvested from wild plants an issue for conservation manag ers is whether sufficient seeds remain for population replacement, especial ly if it is subject to recurrent disturbance. Field data on the effect of f lower picking on seed availability over 13 years were available for the mos t heavily exploited wildflower in Australia, Banksia hookeriana fire-killed shrub restricted to a 2000 km(2) area in the northern sandplains of southw estern Australia. These were combined with demographic data from 14 long-te rm monitoring plots scattered over the landscape. Growing conditions were t ermed 'good' to 'poor' depending on how they affected the number of inflore scences produced, and recruitment of young plants. A computer model was dev eloped based on best-fit equations for all key processes accounting for see d and seedling production and loss. The model indicates that self-replaceme nt (maintenance of a stable population size at a given age from one generat ion to the next) is unlikely for the first 5-11 years following fire, depen ding on growing conditions, even in the absence of picking. Picking has lit tle effect on the minimum fire interval for self-replacement under good gro wing conditions, but, under poor conditions, minimum fire interval rises fr om 12 years at 0% picking to 20 years at 30% picking. Miscalculation of the intensity of picking allowable could have serious consequences for conserv ation of wild populations, as fires are most likely at 10-20 year intervals . A second computer model took inter-fire establishment into account. It ga ve 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 conserva tion authorities in setting the age to first picking and the levels of pick ing permitted for wild populations of Banksia hookeriana. Our models are su itable for a wide range of vulnerable, fire-killed species at present harve sted from the wild. (C) 2001 Elsevier Science Ltd. All rights reserved.