A method for the estimation of the global population sizes of plant species – the Area-abundance-index



The aim of this study is to establish a practical index that considers both the size of the global range, and the mean relative abundance of species within their range. Detailed general distribution maps provide the basis for a classification of ranges into nine size categories. The abundance data are arranged into five categories, ranging from very rare to very common. These categories are derived directly from floristic literature. The Area-abundance-index is calculated using an empirical formula, i.e. by the addition of the mean relative global abundance and the range size category number. Values of the index range from 2 (very rare and range ≤10 km2) to 13 (very common throughout and range > 107 km2). The main advantage of the index is that species become comparable in terms of their global population sizes. Frequently, regional Red Lists contain species that are common elsewhere and occupy wide areas, or may not include locally abundant species that occupy only very small geographical ranges. The application of the Area-abundance-index for the prioritizing of species within Red List categories and, hence, a varying assignment of conservational efforts, is discussed. Furthermore, the application of the index on a local scale, and the regional responsibility for species conservation or monitoring are discussed.