AN EVALUATION AND MODIFICATION OF WORLD CONSERVATION-UNION-RED LIST CRITERIA FOR CLASSIFICATION OF EXTINCTION RISK IN VASCULAR PLANTS

The World Conservation Union (IUCN) Red List criteria endorsed in 1994 consist of a set of decision rules based on quantitative thresholds o f population size, distributional range, rates of decline, and extinct ion risk. I evaluated these criteria using data on 68 vascular plant t axa from southeastern Australia and found that deficiencies could be o vercome with modifications that did not substantially alter the struct ure of the IUCN rule set. These modifications included smaller distrib utional thresholds appropriate to sessile organisms, inclusion of life -history and land-based attributes, an amendment to account for skewed metapopulation structure, and inclusion of a rule addressing number o f populations and qualitatively defined classes of threatening process es. I reviewed the strengths and weaknesses of decision rules for risk classification such as those endorsed by the World Conservation Union compared with intuitively based qualitative schemes in traditional us e. I concluded that explicit schemes foster greater accuracy and preci sion in risk classification, are more defensible in the face of challe nges, and define an agenda for data collection that is essential for t he ongoing assessment and management of threatened species.