Regional priority setting for rare species based on a method combining three criteria

We propose a method to establish regional-level priorities for plant species that is based on three criteria. These involve two main criteria associated with species rarity, (a) small range size and thus regional responsibility and (b) low population numbers and thus local rarity, and a third criteria associated with habitat vulnerability to distinguish species currently threatened by human activities. Application of the method shows how the three criteria can be objectively and readily quantified (using a system of equal numbers of ranks) and combined into a hierarchy of priorities. We show how this can be done by using regional responsibility as a first order priority followed successively by local rarity and habitat vulnerability. Since the criteria are closely associated with rarity, this method is easily understandable for decision makers. We illustrate the application of the method to plants (a species rich group) at two regional scales where the objectives are different. If adapted to the availability of different types of data, the three criteria could be used to produce comparable lists in different countries and regions.