Revising Ellenberg's indicator values for continentality based on global vascular plant species distribution

QuestionsMisunderstandings and methodological inconsistencies have hampered the applicability of Ellenberg's biogeographic indicator values for continentality. To redefine the indicator values we focused on the following questions: (1) what is meant by phytogeographic continentality as the basic principle behind Ellenberg's indicator values for continentality; (2) can we redefine the continentality indicator values based on an assessment protocol rendering the values more reproducible; and (3) what are the differences between Ellenberg's indicator values for continentality and the redefined ones as a statistical data set, and in application? LocationNorthern Hemisphere, Central Europe. MethodsBiogeographic indicator values are based on global species distribution data. Species' distribution information is converted to standardized range formulas that combine information on occurrence across floristic zones, altitudinal preferences and the distribution within the oceanity-continentality gradient. Improved and revised range formulas are converted to new indicator values for continentality (C-value) using simple algorithms. ResultsNew indicator values for continentality (C-values) and amplitudes for 2984 taxa of Central European vascular plants are presented. The main improvement is the application of a comprehensible assessment protocol. The new C-value gained a more balanced frequency distribution, rendering it more useful for broad-scale biogeographic analysis. ConclusionsFor the first time, biogeographic indicator values derived with a consistent method that is based on distribution data are presented. Occurrence information and vegetation data are becoming increasingly available globally, while changing climatic conditions inevitably accelerate species range dynamics, and therefore the application of biogeographic indicator values will increase.