A graduated nativeness definition for overcoming dilemmas and difficulties of vascular plant species

Nativeness is a concept central to biodiversity conservation and invasion biology, but there are several problems related to a classic binary nativeness definition. Dilemmas arise from the dynamic nature of species' distribution ranges on longer time scales, and difficulties arise in the application to smaller regions defined by arbitrary borders, and limited knowledge of species' past distributions, their natural migration potential, and time or mode of arrival in an area.To remedy these shortcomings, we propose a graduated definition of nativeness, where non‐native species in a focal territory are categorized as either ‘near‐native', ‘distant‐native' or ‘alien' based on geographical proximity to areas where they are native, their migration potential and climatic niche. As an example, we apply 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). A change in nativeness status for single species could have practical management implications. More importantly, taking the non‐equilibrium spatio‐temporal nature of plant distributions into account allows for a more consistent concept of nativeness, which has the flexibility to accommodate future changes in species distributions induced by climate change.