A graduated nativeness definition applied to the vascular flora of Denmark

The data were used to exemplify how a graduated definition of nativeness (native, near-native, distantly native, alien) differs qualitatively and quantitatively from a binary definition (native, alien). The motivation to revise the definition of nativeness comes from insights into problems related to the classic binary nativeness definition. These problems arise from the dynamic nature of species’ distribution ranges on longer time scales, from the application of the binary definition to smaller regions delimited by arbitrary borders, and from limited knowledge of species’ past distributions, their natural migration potential, and time or mode of arrival in the focal area. To remedy these shortcomings, we have proposed a new graduated definition of nativeness, based on geographical proximity to areas where species are native, their migration potential, and climatic niche. We applied the graduated definition to the vascular flora of Denmark, reclassifying species as ‘native’, ‘near-native’ (native to countries in close vicinity, within their natural migration potential and with similar climatic niche to the focal territory), ‘distant-native’ (native to countries in the rest of Europe) or ‘alien’ (native to other continents).